the ammonite shell: its structure, development and biological

C Y PR IAN K ULl CKI
TH E AMMONITE SHELL: IT S STRUCTURE, DEVELOPMENT
AN D BIOLOGI CAL SIGNIFI CANCE
Abstra ct, - T he a ut hor's stud ies on the dev elopmen t of the sipho n a nd relat ed st ructures in Tri assic a nd post-Triassic
ammo nites re vea l that, contra ry to th e views of M UTV EI ( 1967) a nd MUTVEI and R EYMENT (1973) th e s ipho na l tube in
the prochoa nit ic stage of develo pme nt is ho mologou s to t he organic layer of th e sipho na l tube of Recent Naut ilus.
Dur ing the tra nsitio n fro m retro eh oan itic to prochoanitic septa l necks, a dee p furro w enc ircling th e siphonal soft tissue
develo ped with in th e posterior ep itheli um of ammon ites . It d ivided th e ini tially synch rono us zo nes secr eting th e nacreou s
tis sue o f the septum and sipho na l tube into zones wh ich cou ld secrete asynch ro no usly. Suc h asynchronous secre t iona l
activity was assoc iate d with the d ifferen t org an ization of the so ft tissues in th e posterior pa rt of the body, a nd ena bled the
an ima l to bo th ac celerate a nd retard sipho na l tube for ma tion on ei ther th e in tern al or the extern al side , an d a lso
a llo wed the po ssibility of connectio ns between the siphon and vario us a uxilia ry structures (e.g. sipho na l me mbranes).
A uxilia ry deposit s in proch oa nitic ammon ites arc a lways bipartite. Poste rior a uxiliary deposits a rc homol ogou s with
the d istal end o f the retroch oani tic sep ta l neck , wherea s th e a nterior a ux ilia ry deposits co rre spond to the auxi lia ry r id ge
of Recent Na utilus. T he result s of the a ut hor's stud ies on th e early deve lo pmen tal sta ges of the a mmon ite she ll differ
fro m tho se o f I3 IRKELVND (1967) , Bm KELUND and H ANSEN ( 1968, 1974) a nd ERllEN c l al. (1968, 1969). Th e wall prop er
of the init ial chamber is show n to pa ss contin uou sly into the external prismat ic layer of the firs t who rl, a nd is a co unter pa rt of the external pr ism at ic layer o f the succeed ing whorl s. W hen a co mp lete initial chamber is develo ped behi nd the
zone secret ing the wall pr o per of th e initia l ch amber and the external pri smat ic layer of the first whorl, a bro ad zo ne
a ppea red secreting pri smatic a nd subprisma tic tissue. T h is tissue b uilds t he interna l co mponen t of the ventral wa ll of
th e .in itia l chamber an d, a t the sa me time , the main wa ll co mponen t o f the first whorl an d proseptu m. Th e proseptum
originated in a deep furr ow en circli ng the posterior pa rt of the bo dy as a co ntinua tio n of the inte rna l pri sm ati c la yer
of the in itial cha mbe r and the first whorl. Du ring la ter develo pment , the po sterior secre ting zo ne was di vided int o the
zone sec reting th e subprismat ic tissue of the first whor l wa ll, the externa l co mpo nent o f the dorsa l wa ll, a nd th e zo ne
secre ting septa a nd th e interna l pr ismatic layer. In lo ngitu di nal sectio ns th e externa l layer of th e initial ch am ber wa ll
is equiva lent to the dorsa l wall of the first whorl; the thickness dec reases co nside rably a t the bo undary between th e
ini tial chamber a nd the first whor l. Th is microst r uct ure reflects a change in the secretory pa ttern o n th e nep ioni c constr ict ion . Th e cha nge invo lved on ly the subzo ne co ntrolling the secre tio n of th e subprismatic layer o f the first wh orl.
T his layer corresponds to the nacreou s layer of the fo llow ing who rls. Observa tio ns on she ll em bryogeny pro vided ne w
evidence su ppo rt ing th e idea of a d irec t embryonic develo pment of a mmonites a ga inst the hypoth esis of la rval developme nt a nd metamorpho sis of ERHEN cl al. (196 8, 1969). As a result of the presen t a uthor's experi men ts with th e grad ua l
filling of empt y Quenst edto ccras shells wit h water it has been de mo nstrated tha t the flu id di stri butes eq ua lly in numerous
reservoirs on the margin of septa near the she ll wa ll and ad heres th ere th ro ugh surface ten sion. Su ch a distri but ion of
th e fluid as sures a n inva ria ble degree o f deco upling of the mai n fluid vo lume fro m th e fluid encircli ng th e siphon. Thi s
makes the hydrostatic appara tus of the a n ima l functiona l in va rio us shell po sition s an d en sures sta tic eq uilibrium in
a tu rbulen t env ironment.
CONTENTS
Page
In tr od uct ion . . . . .
Acknowledge ment s
M at er ial an d me tho ds .
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P a la e on t o lo gin P olo nic a No . 30
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CY PRIAN K ULlCKI
Siphona l deposits
O bserva tions. .
Septal necks and o ther sipho na l elements in Na thorstites gib bosus
Description . . . . . . . . . . . . . . . . . . . . . . . .
T he rela t ion of co nnect ing ring to septa l neck and scptum . .
Di scont inuities observab le in sectio ns of septa l necks or in their proximi ty
Septal neck s a nd siphona l deposits in Qucnstedtoccras and Kosmo ccras , . .
D escr iption . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
On toge netic development on sep ta l necks in Quenstedtoceras a nd Kosmo ccras
Ca ecum and its attache me n ts to the she ll . . . . . . . . . . . . . . . .
S upplemen tary a uachernent s bet ween the connect ing ring and the shell . . .
A siphon fro m the bo dy cha mb e r o f H olcopliylloceras zignodianum (d 'ORIlIGNY)
Di scu ssion an d in terp reta tion . . . . . . . . . . . . . . . . . . . . . . . .
Co mparison of re trochoa ni tic septa l necks of Na tltorstitc s, Nautilus and o the r na uii loid s
On togenet ic develop men t of septa l neck of Nath orstites .
. . . . . .
Fo rma tio n of proch oan it ic septa l neck s in a m mo nites . .
. . . . . .
Ontogenetic grow th of the con nec ting ri ng 'in tran sitiona l ph ase in Nathorstitcs
Ontogen y of prochoanitic sep ta l neck of N atltorst ites . . . . . . . . . . . .
Ontogeny of sep ta l necks a nd a ux iliary de po sits in Quenstedtoceras a nd Kosmo ccras
Th e last formed sectio n of the s ipho n
Int erp ret at io n a nd co nclu sions.
Embryo nic she ll . . . . . . . . . . . .
O bser vat ion s. . . . . . . . . . . . .
Th e str uc ture of the init ial cha mbe r a nd the first who rl up to th e end of the nep ion ic swe lling in Quenstedtoceras
a nd Kosmoceras ,
Ini tial cha mber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fi rst wh orl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Th e str ucture of th e she ll a fter the nepion ic swe lling in Quenstedt oceras and Kosmo ceras
Vent ral wa ll .
D o rsal wa ll . . . . . . .
Septa . . . . . . . . . .
Di scu ssion an d int er pretati on
Initial cha m ber . . . . .
Do rsal wa ll . . . . . . .
Th e zo ne secreting the externa l co m po ne nt of the dorsal wa ll
Wrink le-layer . . . . . . . . . . . . . . .
Se pta . . . . . . . . . . . . . . . . . . .
Th e mode and forma tion of the initi al cha mbe r a nd the first who rl a nd their development
Th e q uestion o f ea rly develo pmen t in a mm oni tes . . . . . .
Th e fun ction al im port a nce o f fo lde d sep ta . . . . . . . . .
I nterpretati o n of func tio na l significa nce of septa l co rr ugat ion
R efer en ces . . . .
Ex pla na tio n o f the pla tes . . . . . . . . . . . . . . . . .
Pl at es 24- 48
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INTROD UCTIO N
The use of th e sca nning electron micr oscop e (SE M) mad e possible a marked increase in
th e accuracy of stud ies of the microstructure and ea rly development of the amm onite shell.
SEM stud ies on the early devel opment of a mmo nites were ca rried out by BIRK ELUND (1967) ,
BIRKELUND a nd H ANSEN (1968, 1974), ERB EN', FLA JS a nd SI EI-I L (1968, 1969), DRUZ CZI C and
KHIAMI (1970) , DRUZCZI C and DOGU ZH AEVA (1974), K ULl CKI ( 1974, 1975) and DAUPHIN (1975) .
The material co vered by the se st udies was of widel y differin g ages a nd m odes of pre ser vation ,
and interpretation s of structural detail s and early growth in these pa pers vari es wid ely, a ltho ugh
there is gen eral agreement in respec t of other features.
Th e studies carried out by th c pr esent a uthor deal with well-preser ved specime ns of Quenstedtoceras, Kosnioceras a nd other Callov ia n (J urassic) a mmo nite genera from well-known
locality at Luk ow, eastern Poland. The work permitted a revision of cur rent views on the
nature of the ea rly ontogenic gr owth stages o f a mmo nites.
T HE STIW CT U RE AND D EV EL OPM EN T OF A M M ON ITE SHEL L
99
A detailed anat omica l study of the earl y growth stages allows recon structi on of ontogenic
development of zones of secretion a nd casts some light on the embryogenesis of the group.
Num erous specimens of Quenstedtoceras with unmineralized interiors were used in experiment s which involved infilling of phragmocone chambers with water. Thi s gave inform ati on
on the functio n of folded septa from both physiological and mechanical points of view.
The characteristics of the perio stracum and some other organic films not related to the
siphuncle are omitted below becau se of their va riability throughout the shell. There is some
evide nce for diagenesis and seconda ry mineralizati on of the organic films which is reflected
by differences in thickne ss, resistance to etching by various chemical reagents, as well as their
absence in some part s of shell. Thus the question of organic films is con sidered as requiring
separa te treat ment.
The termin ology wide ly used in the literature is accepted here except for following new
terms :
ncpionic ., wellillg - for shell thi ckeni ng» on th e ncpi oni c co nstrictio n;
tissue - for min er a l a nd o rgan ic ma tter fo rm ing se pa ra te shell layer s :
posterior auxiliary deposits - for a uxi lia ry dep osit s fo rm ing th e a nterio r end o f th e connecting ring ; the name is ch osen
because o f the post eri o r positio n o f these dep osits in re la tio n to th e se pta l neck , a nd it is equi va lent o f th e ter m " ma nzhcta "
used by D RUZ CZ IC et al. ( 1974, 197(,) ;
anterior auxi liary deposits ,- for a uvilia ry dep osit s forming the poste rio r end o f th e co n necting ring ; th c nam e is cho sen
beca use th eir posit ion is o ppo si te to th at of the po sterior de posi ts:
angular deposits - for m ineral deposi ts occurring between p ro xim al part o f a proch oanitic neck a nd the po st erior a uxiliary de posits:
wall proper of the initial chamber - fo r the or igina l wa ll of th e initial cha m ber.
Th e specimens covered by these studies are housed in the Institute of Paleobi ology of the
Polish Academ y of Sciences abbreviated as ZPA L. SEM micrographs were made using the
micr oscope J.S.M.-1 in the Lab orat or y of Electron Microscopy, Nencki Institute of Experimental Biology, Polish Academy of Sciences in War saw.
AC KNOW LE DGE MENTS
Gr at eful ackn owledgements are expressed to Professor H. PUGACZEWSKA (Za klad Paleobiologii PAN, War szawa ), and Professor H. Mm 'vEI (N aturhi storiska Riksmuseet, Stockholm)
for discussion s a nd readin g thc manu script. Special thank s are due to Dr . W. J. KENNEDY
( Department of Ge ology and Mineral ogy, Oxford University) for valuable comme nts a nd
improve ment of the language. Thanks are a lso extended to Dr. M. V. KORTCHINSKA JA,
Dr. N. I. SHULGINA (In stitute of Arctic Geo logy, Len ingrad), Or. G . K. KABANOV (Paleontological Institute' SAS, Moscow), and Or. I. D. CER ETELLI (In stitute of Paleobiology Georgian AS, Tbil isi) for supplying materi als. Specia l thank s are due to Or. M. F. BOGOSLOVSKAYA, Dr . B. I. BOGOSLOVSKY (Pale ontological Institute SAS, M oscow), Or. I. S. BARSKOV,
D r. L. A. DOGUZI-IAEVA , a nd Professor V. V. Da u zczic (D epartment of Geology, Moscow
Uni versity) for discussion and making available their collection s. The technical help of following persons is menti oned with grat itude : Mr s. M. RADZIKOWSKA and Mr s. E. WYRZYKOWSK A
(ph ot ograph s), Mr. Z. STR/\K (thin sections), Mr. W. SICI NSKI (plat es), a nd Mr s. K. BUDZYNSKA
(drawings). Th e SEM microgra phs have been made at the Lab oratory of Electronic Micr oscopy
of the Nencki's Institute of Experimenta l Biology in War saw.
MAT ERIAL A N D METHODS
The studies covered the following specimens :
(I) Nathorstites gibbosus STOLLEY; Carnian (Upper Triassic), Odgeoya Island (E Svalbard) ;
two specimens, one of which was infilled with calcite a nd very well preserved , were studied
using the SEM ;
7"
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CY P RIAN K UU CK l
(2) Holcophylloceras zignodianuni (d 'ORBlG0.'Y); Ca llovia n (M iddl e J urassic) , Rat scha villa ge
in the Setsisk vile va lley, G eorgian SS R; two specime ns, one with we ll preserved siph uncu lar
tube in the body cha mber.
(3) Quenst edtoceras sp .; Ca llov ian (M idd le Jurassic) , Lu ko w, Pol an d; numerous specimen s
were used fo r m aking 100 polished sec tion s; SEM studies covered 27 polished sectio ns and
23 fr actured speci me ns .
(4) Cadoceras sp .; Call o vian (Middle Ju ra ssic), An aba r valley, Siberia, USS R; 3 polished
sec tio ns.
(5) Kosmoceras sp. : age an d occ urrence as (3); 10 poli sh ed secti ons (4 used in SEM st ud ies)
and 8 fractured su rfaces.
(6) Perisphin ct es sp.; th e age occ urrence as (3); 8 fractured sur faces.
(7) Polyptychites sp. ; Lower Yal an gini an (Lo we r Cretaceous) , m outh of th e Anabar, Siberia ,
USSR ; o ne pol ish ed sec tio n.
(8) Di chotomites sp . ; U ppe r Yala ngini an (Lower C re ta ceo us), Baj a rka Vall ey, Siberia, USSR ;
on e p oli shed secti on.
(9) Surite s subanalogus SCHULGINA; Bcrriasian ( Lo wer C re ta ceo us), Bajarka Valley, Siberia ,
USSR ; o ne polish ed sec tio n .
(10) A coneceras traut sclioldi SINZOv; Aptian ( Lower C retaceo us), Ulianovs k, right ban k o f
Volga , USS R; three p oli sh ed sec tio ns .
The speci mens used for S EM in vesti gati on were prepared as foll o ws: (a) t he frac tured
sa m ples were a ttache d d irectl y to th e sa mple holder usin g elec tro-cond uc tive glue a nd sub seq uen t ly coated w ith evapo ra ted ca rbo n and go ld; ( b) po lished sections were et ched for
2-5 m inutes in 2 % EDT A a nd subseque ntly a ttache d a nd coated as (a) ; (c) acetate peels o f
large p oli shed fragm ents we re taken a nd pi eces stuc k to th e sam ple h older an d si m ila rly coated .
The a na lysis of m ineral co m posi tio n (STAH L a nd J ORDAN, 1969) ha s shown th at the shell
o f Quenst edtoceras fr om Lukow co ns ists pri ma ri ly of arago nite a nd th a t o nly 2-4 % calcite
is present. This in di cat es that rec ryst alli za tion was slight , a nd that the st ruc tu re observed are
largely o rigina l.
SIPHO N AL D EPOSITS
OBSERVATIONS
Se ptal necks and other siphonal elements in Na thorstites gibbosus Stolley
Description. - The positi on o f th e siph o n is a t th e ventral m argin fr om the p roseptum
o nwa rds in Na tho rstites gib bosus . M edi al sec t io ns sho w tha t th e ven tra l part o f se pta l necks
is clo sely adjoined to th e int ern al su rfac e of th e wa ll, wh er e its thi c kn ess is reduced in r elation
t o th e d orsal pa rt. This red uc tio n in thic kn ess re sult s in the fac t tha t part icula r elem en ts of
necks a re less clea r in th e ve ntra l part a nd the desc ripti o n of necks is therefore m ainly based
o n sectio ns th ro ug h th e d o rsa l part.
In N. gibbos us th e first tw o se pta a re sit ua ted o ne a bove th e another in the d o rsal part.
They b ifurca te as they approach the caecum o rganic co ver of the siphuncle (p l, 24 : 5). A ny
m ore d et ailed determi natio n o f the characteristic s of the si phona l dep osit s a nd septal neck s
b ased o n these septa is no t po ssibl e. W ell- develo ped retroch oaniti c septal nec k s p ro per are
well di splayed o n succes sive se pta. Fro m th e morphologica l po int o f vie w th e re trochoanitic
neck represents an ex te nsion o f th e sept u m d ir ected to ward s the apica l part of the she ll (pI. 24:
1-3 ; figs. I A-G, 2). From th e forty secon d septu m (o r 3·75 of who rl on wa r ds) a sharp m a rg in
appears in th e ventral part o f th e anterior part o f th e sep ta l nec k , g ra d ually disap pearing
somew hat bel ow th e mid -h e ight o f the neck (fig . I E) . This sharp m argin fr om th e a nterior
T ilE STRUCT lI P.[ A ND DL VELOP MLn i or A M MON ITE SHEL L
101
:
rr~
' ." ;
A
~>
.
17"
".:
:
~.: .. . :: ..
..:..•:.;-::.:.&.:~ ....... .": ....:..:,.
~ ~.:~
fi g. I
Sch eme o f the sec tio ns o f sep ta l n'x k s III Nathorst itcs g ih!w \!lI' , Z I'A L Am 1I1 / ~ . A - 18 th scpt um , rct ro choa nitic septal
neck . B - 20t h sc ptum , rctrochouniric septa l neck; an exceptio na lly well develo ped anterior au xilia ry sipho na l deposit
is visi ble. C - 32nd sc ptu rn. a rctroch o a nitic se pta l nec k. D - ~ 9th scp tu m , a sha r p rid ge po inting a ntcrio rly occurs
in the ve nt ral par t of th e ncck : it d isappears a t the mi d-po int o f th e nec k. E - 42nd scpt um , th e ridge d isappears a littl e
h igher th an in D . F - 451h sc ptum . ;) sha r p edge extends to th e e nt ire perim eter of the neck, a t th e dorsa l side it is in
th e fo rm of a slight ap i' :·;ld i.". G - 49th scptum. f-f - 50th sc p tum, the sha rp ridge is a t a height suffic ient to form
a dis tinct nrochoa nit ic c lement o f the scrual neck. 1 - 55th sc ptum , tlw proc ho a nitic clem ent o f th e sc pta l neck is bertcr
deve lop ed tha n in t he curlier scpta , K - 89th sc ptum , a typica l prochoa n itic se pta l neck
102
part of th e neck is marked along the whole per iphery of the neck, including its dor sal part ,
at septum 45 (end of the four th who rl). The ma rgin is marked as a sma ll projec tion towards
the anterior in medial section through the dor sa l par t (fig. I F ). It increases in height on successive septa and finally becomes simi lar to the ending typica l of pr oc hoanit ic septa l necks
(fig. I H, J).
Further growth leads to the development of a prominent proc hoanitic neck at the expe nse
of the equivalen t of the retrochoani tic neck. As a result of proportional reduction the latt er
become s modified int o a typical poster ior auxiliar y deposit (pI. 25: I ; fi g. I K).
The relation of connect ing ring to septal neck and scp t uni. - The ending of the ret roc hoa nitic
septal neck extend s a nd passes into the posterior section of connect ing ring (pl , 24: I ; fi g. I A, B).
The anterior section of the con nectin g ring is attached to the inner surface of the a nterior part
B
/
Fig. 2
Di agramma tic dra win g of the la st two septa in Natliorst itcs g ihbusl/\', a t the stage of rc tro choan iuc se pta l neck s. A - - T he
last scpturn u nder formati on. B -- Th e la st but o ne scp tum co mp le tely formed
of the septal neck (pI. 24 : I, 2 ; fi gs. I A-E). A small project ion is visible at the place where
the ante rior section of the co nnecting ring is a ttached (pI. 24 : I, 2, 3, 6, 7 ; fig. I).
The anterior end ing of the posterior part of the connecti ng ring a nd the poster ior ending
o f the next following con necting ring are distant from one another on the earlier septa, but th e
distan ce decreases with furthe r growth. When prochoa nitic septa l necks are formed the siphuncle gain s add itional conn ect ions to the neck a nd septurn as :
(I) the dist al end of the prochoanitic septa l neck is co nnected with the connecting ring by
a short section of organi c memb rane (pI. 24: 4 ; pI. 25 : I, 2a ; fi g. I K).
(2) the conn ecting ring is fused with t he organ ic cover of the internal surface of the septa l
neck in its mid-length (pI. 25: 2a . b ; fi g. 3 D -G) ; th is con nection may wide n to wards either
the back of the neck (pI. 25 : I) or its fron t (fig. I K) with furth er growth.
(3) the adapical septal surface becomes fused with the connecting ring via the so-called sipho nal
membrane. Thi s conn ection is more or less regular in characte r (pI. 25 : I ; fi g. I K).
Discontinuities observable in sections of sep tal necks or in their proximity. - T he minera l
tissues of the specimen studied are almost completely recrystallized, which preclude s any
a nalysis of the mutual arra ngement of mineral compo nents a nd their accurate identificat ion .
It should be not ed, however , that there ar e regula rly repeated discontinuities on successive
septa . Taking into account hypotheses previ ously put for ward, these bou ndaries may be considered not as diagcnctic but rather primary in origin . T he boun da ries are visible under both
o ptical and sca nning electr on microscope .
TH E STR UCT UR E AN D DE VELOPMEN T OF AMMONI T E SH ELL
103
Sections of the dorsal part of th e septal neck from th e stage of occurrence of retrochoanitic
necks display a single di scontinui ty exte nd ing from the a pica l surface of the septum to the
inner side of the neck (pI. 24 :, I, 2, 3, 6, 7). Th e di scontinuity separates the apical part of
the retrochoanitic neck from th e sept urn a nd its proximal part, which is ma rked as a minor
elevation above the ad api cal surface of sept um.
In the transitional zo ne where the prochoanitic septal necks o rigina te, the discont inuity
divides the au xiliary de posits formed from the retrochoan itic part of th e septal neck into two
parts: the posterior, giving rise to th e posterior secti on of the con necting ring, and the anterior.
With further growth, th e discontinuity becomes less and less clear, and finally disappears
completely, givi ng a n appa rentl y ho mogene ou s appea rance to the auxiliary deposits originating from the di stal part of retrochoanitic septal neck. Di scontinuities running from the apical
septum sur face still occur repeatedly in the tr ansitional zo ne (pI. 24: 4; fig. I H, J) ; they continue from the angle form ed by th e auxiliary deposit and the proximal part of the septal neck
towards it s di stal par t in th e prochoanitic stage, becoming subseq uently obliterated (pI. 25: I ;
fig. I K). The di scon tinu ities separ ate the auxiliar y deposit from the prochoanitic septal neck.
Septal necks and deposits in Quenstedtoceras and Kostnoceras
Description. - In Quenstcdtoceras the relati on ship between the first two septa differs from
that between the subsequent one s, because of the reduced distance between them and the
distinctive curvature of the first septum. The central part of the dorsal side of the second septum
grows int o the proseptum at 50- 60 % of it s height (pI. 27: 4) and not directly to the wall of
the initial chamber. For thi s reason a ll sectio ns parallel to the medial plane passing through
siphon and caecum display onl y the ventral part of the second septum and the ventral wall
of the first segment of the connecting ring, togeth er with the siphonal deposits. The siphonal
portion connecting the proseptum a nd seco nd septu m re presents an oblique segment of the tube.
In medial secti on s, the caecum is connected with the ventral wall of the initial chamber
a long a sh or t sect ion of var iable width (pl, 28: 2; pl. 44: J). Jn these sections, the ventral
part of the pr oseptum is generally so sho rt th at it is d iffi cult to sepa rate it from the shell wall.
In places where th e caec um grows int o t he vent ral wall and proseptum , the organic wall of
the caec um may thin (pl . 28: 2) o r thicken (pl , 44 : I), but there are no mineral deposits
connectin g the caecal wall a nd th e min eral t issues of t he prosepturn or the wall of the initial
chamber. T he dorsal pa rt of th e circum-siph on al pr oscptum is represented by a plate somewhat
bent in th e direction of ape x or a perture (pI. 29 : I, 3 ; pl. 36 : I ; pI. 36: 3). A posterior auxiliary deposit occurs bet ween th e o rga nic caecum wall and th e mineral tissue of the proseptum
(pl, 29: 3; pI. 30: I; pI. 31 : 2 ; pl, 36: 1, 3; fig. 6, 7 E, F ). The min eral tissue of the posterior
auxiliary deposit is visible o n cro ss-secti ons as a finely granul at e mass of randomly arranged
elements. It resembles the min er al tissue sepa ra ting th e subprismatic and pri smatic layers of
the initial chamber, a nd th at sepa ra ting th e first who rl from the basal and middle parts of
proseptum.
The wall of the connecting rin g visibl e in th e ventral part of th e medial section connects
the first and second septa. The a nterior auxiliary deposit of th e proseptum is relatively well
developed between the wall of the connecting rin g and the proseptum. It is variable, usually
irregular in shape a nd mo re o r less antero-posterio rly elongated. The mineral tissue of the
anterior auxiliary de posit of t he prosep tum is mo re regular in texture, so mewhat resembling
nacreous tissue , with interlamellar spa ces ori ented conco rdantly with the walls of the connecting ring, or prismati c tis sue with the lo nger axes of min eral components lying parallel to one
another and th e wall of th e connect ing ring (p I. 28 : 2; pI. 30 : 2; pI. 38: I a : pI. 39: I; pi 44 : 3).
In medial section th e ventr al wall of the connectin g ring of the first segment is connected
by its ante rio r ending with t he posteri or a uxilia ry deposit of the second septum. In that section
104
C YPR IAN K ULl CKI
the posterior auxilia ry deposit of the second septum has the outline of acute-angled triangle:
the anterio r margin of the con nect ing ring is adjacent to the sho rter arm of the triangle and
the intern al side of the vent ral wall to one of the longer arm s (pl , 38: I b; pl . 39: I ; pl. 44: 3).
Th e mineral tissue of the pos terior a uxiliary de posit of the second septum does not differ from
th at of the a nteri or au xiliary de posit of the pr oscptum . Th e sections show n here (pl. 28 : 2;
pl. 39: 2; pl. 30: 2) displa y ma rked shorte ning or ab sence of a segment of the co nnecti ng
ring . In the second or thir d case the an terior ..uxiliary depo sit of the proseptum passes smoothly
into the posteri or de posit of the second septum.
Th e anterior a uxiliar y depo sits of the second septum ar e triangular in outline in medial
section. They are part ly developed on the post er ior a uxiliary deposits and partl y on the ventral
shell wall. Th e structure and text ure of these dep osits remai n poorly kn own , but seem somewhat
different to that of the mine ral tissue of the au xiliary de posits described above (pI. 38 : I b ;
pl. 39 : I).
The dorsal section of the conn ecting ring connect s the anterior auxiliary deposit of the
proscpturn and the posterior a uxiliary deposit of the th ird scptum in med ial section. The
mineral tissue of the a nterior depo sit of the proscpium is the same here as ill other parts of
the section, although its sha pe a nd place of attac hmen t to the pro septum are somewhat variable.
The do rsal part of the a nter ior a uxiliary depo sit is situated either below the free prosepturn
margin (pl , 28 : 3 ; pl. 29 : I, 3 ; pl. 30 : I ; pl , 3! : 2) or represents a n extension of the for ward s
bend of the proscp tum which p:... xluces the appa rently proch oan itic septa l neck of thi s part
of the prosept um (pI. 36: 3).
Th e subdivision of the au xiliar y dep osits into a nterior and posterior par ts is ma rked
throughout the ontogeny in Quenstedtoceras a nd Kosn ioceras, as it is during the prochoanitic
necks stage in all repr esentati ves (II' A nu no ni ti na, l .yt oceratina and Pliyllocera tina studied by
the present auth or .
O n some ventral sections or the first half of the first whorl or Quenstedtoccras a nd Kosniocents the a nterior a nd posterior au xilia ry deposits ar e of identical develo pment relat ive to th e
septal neck (pI. 32 : I: pl. 34 : 1,2 ; pl. 35 : 4) al though differences in size develop subsequently.
Thi s rellects a more extensive developm ent or anterior than posterior a uxiliary dep osits (pI. 33: I ;
pl. 32 : 2 a ; pI. 35: 2; pl. 37: 1, 2), and is seen already in the do rsa l part of sections of the third
scptum (pl. 35: 3).
T he posterior auxi liary depo sits are usually covered. to a minor deg ree by the anterior
ea rly in development (see e.g. pI. 32 : I); subsequently, the an terior deposits meet the posterior
a long their who le length (pI. 32 : 2a; pl. 33: I ; pI. 35 : 2; pl. 37: 1, 2).
Th e mineral t issues of au xiliary deposits from middle a nd late ontogenetical stages arc
still poor ly known. The genu s KOSIlIO CC'J"ilS (pl. 4 1: 1- 3) is an exception, however, for on scpta
of the sixth whorl the posterior a uxiliary deposits arc marked ly larger than the anterior. Th e
bounda ry betwee n the posterior and anterior de posits is very sha rp , and a ngular deposits
arc well developed within the angle between the posterior auxi liary dep osits and the proximal
part of the septal neck.
The mineral tissues of the posterior au xiliary deposits closely resemble the modifie d
nacreou s layer of the dista l part of the septal neck of 'l Pseudorthoc eras illustrated by M UI' VEl
(I 972 b,. pI. 7: I) as well as the nacre ous layer of distal end of a septal neck of Na utilus potupilius L. also figured by th at author (M UI' VE!, 1972 a ; pI. 2 1: 1-2; pl, 25; I).
In the case of Kostnoceras. the posterior aux iliary depo sit differs from those figured by
M UTVEI in hav ing a more homoge neou s structure throughout the section as well as in having
fewer organic membran es (co rres ponding to interla mellar membra nes). Th e mineral tissue of
the posterior a uxiliary deposits of the specimen of Kostnoceras studied a rc best termed
sphc rulitic-prismatic (pI. 41 : 3). The anterior au xiliary deposits (pI. 41 : 2) are also unifo rm ly
developed through out the section and ar e structura lly closest to the depo sits of the a uxiliary
ridge of Recent Na utilus po nipilius L. figure d by MUTV EI ( 1972a, pI. 24 : 2). Th e structure is
THE STRUCTURE AND DEVELOPMENT OF AMMONITE SHELL
105
prismatic, without noticeable spherulites and rudimentary transverse membranes such as occur
in posterior auxiliary deposits.
The tissues of the posterior and anterior auxiliary deposits from early stages of ontogenetic
development of Quenstedtoceras and Kosnioceras display more features transitional towards
prismatic and nacreous tissues than those from the lates stages (pI. 32: 2 b, 2 a; pl. 35: 1-4;
pI. 37: I a-I b; 2a-2b). It is often possible to note a structural difference between the anterior
and posterior auxiliary deposits of a single septum (pI. 35: 1-2; pI. 37: 1-2); the difference
is usually small, with the anterior deposits showing more strongly marked prismatic features.
The angular deposits also show a prismatic structure, characterized by a fan-like orientation of the crystalline components in cross-section (pI. 32 : 2; pI. 36: 2; pI. 41: 1). Studies
of Quenstedtoceras and Kosmoceras at various growth stages show a marked variability in
the degree of development of angular deposits, characterized by prismatic structure independent
of ontogenetic stage, mode of development and preservation.
Specimens with body chambers preserved never display a connecting ring in the last
chambers of the phragmocone, although they almost always show auxiliary deposits preserved
on the last septum. The development of auxiliary deposits is relatively weakest here and the
posterior deposits are always stronger than the anterior.
Ontogenetic development of septal necks in Quenstedtoceras and Kosmoceras. - The first
septum (proseptum) of representatives of these two genera shows a free circumsiphonal margin
around the connecting ring, straight or bent slightly backwards or forwards. A septal neck
is not, therefore, developed .
The second septum of Quenstedtoceras also lacks a septal neck (pI. 29: 2; pI. 38: I b;
pI. 39: I), but additional deposits in the anterior part, above the anterior auxiliary deposits
(pI. 28: 2; pI. 30: 2). The latter are built of prismatic tissue similar to but not passing into
that of the septum. The deposits are found only in paramedial sections, and may be homologous with the distal ending of a prochoanitic septal neck.
The third septum may have a typical prochoanitic septal neck with an elevated distal
margin in the ventral part (pI. 30: 3).
Subsequent septa display normal prochoanitic septal necks in their ventral parts (pI. 30: 4;
pI. 37 : I a-2a). The middle growth stages are very often characterized by the distal ending
of the septal neck rising above the surface of the siphonal tube (pI. 30: 4; pI. 31: I). The
formation of prochoanitic septal necks is retarded in the dorsal part in relation to the ventral
part. The third septum (and sometimes subsequent septa) of Quenstedtoceras are characterized by a continuous transition from the nacreous tissue of the septum into the prismatic
tissue of the siphon edge. It does not form a septal neck but only a slight swelling (pI. 35: 3).
Septal necks gradually appear in dorsal part on subsequent septa.
Fully developed prochoanitic septal necks are built of nacreous tissue similar to that of
the remaining part of the septum. The arrangement of laminae of nacreous tissue is highly
distinctive (pI. 36 : 2 ; pl, 37 : I a, 2a-b): adaperturallaminae of the septum continue throughtout the external surface of the neck , up to its distal end , whilst adapical septum laminae wedge
out on the inner surface of the neck base.
The dorsal part of the second septum of Kosmoceras is not located on the proseptum as
in Quenstedtoceras, but directly on wall of the initial chamber, the siphonal opening being
situated at mid-whorl. Because of this the medial section displays the ventral part of the septum,
and the relationship between septum and auxiliary deposits are clearly displayed (pI. 39: 2).
The second septum of Kosmoceras has no septal neck. That part of the septum directly
surrounding the siphon is club-shaped (pI. 34: 1-2). The anterior and posterior auxiliary deposits connect with the septum at a right angle in the dorsal region (pI. 34: 2) ; in the ventral
part the septum meets anterior and posterior auxiliary deposits at an acute angle (pI. 34: 1).
Angular deposits are visible in the dorsal part of the section . The mineral tissues of the
106
CYI'R Ii\N K ULl CKl
second scptum a re esse ntia lly nacreou s ; o nly in the club-sha ped wide ning men tion ed above
is there a tr ansiti ona l, ma inly pri smatic struct ure.
T he circumsipho na l part o f the third scpt um of Kosnioceras is bent forwards in the fo rm
of a prochoanitic septal neck (pI. 35 : 1-2) a nd the distal part o f th e neck also di sp lays a tr an siti on al. nacreou s-prismat ic struct ure . Furth er develo pment of septa l neck s a nd a uxilia ry de posits is the sa me as in Quenstedtoceras.
Caecum and its attachmen ts to the shell. - Th e spherica l, somewhat do rso-ventrally fl a ttened caecum and prosip hon a re enclose d in a ch amber formed by the wal ls of th e initia l
cham ber a nd prosepturn in th e proximit y of the extern al sadd le (s) (see pl. 26: I. 3 a, 4 : pI. 27 : 2).
In addit io n to t he co nnection s wit h pr oscptur n a nd initial ch a mb er wall a lready noted. the
caec um is connected with the initia l cha mber wa ll via the so -ca lled pr osip ho n. A typical
Quens te dtoceras prosipho n resemb les a t hree-wa lled tent , and the o bliq ue wa ll con nects the
ada pical part of t he caec um with the in ne r surface of the ventra l wa ll of th e in itial cha m ber .
Th e two vertical, pa ra llel o r slightly convergent walls con nect the caecum wit h th e ob lique
wall a nd th e inner surface of th e initia l chambe r (p I. 26 : 2; pI. 27 : 1, 2). In th e case o f the
spec imen illustrat ed here (p I. 27: I) t he o bliq ue wa ll o f th e pr osiphon toget her with th e wa ll
of the initia l cha mber fo rm a com plex sut ure : in others. t he co nnection between th e wa lls of
the pr osiph on , caec um and surface of t he initial chamber is co ntinuous (p l. 26: 2, 3a. 3 b ).
T he cross-sectio n (p I. 44 : 3) d isplays a free space a t the con nect ion of ca ecum a nd obliq ue
wall. An a bno rmally deve lo ped prosipho n is show n here o n pI. 26 : I, I a: eve n in this ca se,
however, it is pos sib le to disting uish the ob liq ue wall and a single vertica l wall.
The majo rity of pros ipho ns a re characte rized by longitudi na l wrinkles, and simila r but
m uch fi ner wrink les may be a lso noted o n the surface of th e cae cum (pI. 26 : l a . 3a. 3 b).
Severa l spec imens show the surface of the caecu m connected with the dist a l end of the
flange by a n o rga nic fi lm. The caec um is connected in severa l places with th e ventral wa ll
close to the area o f ventral attachment : similar connecti on s a re much sca rcer in the d orsa l
part (pI.26 :3a; pI. 28 : 3: pl. 29 : I ; pI. 30: I : pI. 44: 3 : pI. 29: 3).
Supplementar y at tachments between connecting ring and the shell . - Besides the above
mentioned a ttac hme nts between co nnecting ring a nd scpt um via auxi liary deposits, there are
severa l ot her attac hments, by mean s of so -ca lled sipho nal membra nes. In Q uenstedtoceras
the co nnecti ng ring is attached with th e ventra l wall by a n or ganic membrane loca ted in th e
pla ne of sym metry from th e third septum o nwards. The membrane freque ntly fails to reac h
th e ends of septa meet ing o nly their ad ap ical o r adapert ura l parts (pl , 27 : 5). A n ad di tio nal,
a nd mor e co m plex co nnection bet ween the siphon, ven tral wa ll a nd sept urn appears a t the
t h ird who rl (p I. 27: 3a , 3 b). Suc h co nnections are not fo und o n subseq uent who rls whereas
co nnections by tr an sverse, so mew ha t obliq ue orga nic membra nes beco mes mor e comm o n.
Sh ort a nd na rrow orga nic membran es co nnect ing the surface of the sipho n with both ada pica l
a nd adapert ura l surface of the sep t urn are relative ly ra re in Quenstedtoceras (see e.g. pI. 27 : 6).
A siphon from the body chamber of Holcopliylloceras z ignodianum (d 'OR BlGNY)
T he specimen st ud ied, 105 mm in d iameter, has a bo ut a th ird of a who rl of bo dy ch amber ,
filled with dar k gree nish limeston e, whilst the phragrnocone a nd t he last section of th e co nnect ing ring a re infi lled with calci te (pl , 40 : I). T he section of th e sip ho n in th e body cham ber
is 16·5 mm lon g. Th e sections of siphon from th e two precedi ng cham be rs of th e phrag moco ne,
measured in th e sa me way, a rc 19·5 a nd 19·0 mm lon g respectively. Th e siph on wall is 35 !.J. m
thi ck at its end ing in th e bo dy cha mber, 121 !.J. m tick in its middle pa rt a nd 173 p. m th ick close
to th e a nte rior a uxi liary dep osits. The t hic kness of the siphonal wall fro m th e last chamber
of th e ph ragm ocon e is 69!.J. m close to th e end of t he a nterio r a uxi liary dep osits of th e last
T H E STR UCT U R E AND D EVELOPM EN T OF AMMONIT E SH ELL
107
septum. T he extern al dia meter of the con nectin g ring fro m the bod y cha mber is 1575 (.I. m a nd
1400 (.I. m close to its termina tion and to the septa l neck respectively. and 1140 (.I. lll in the pro ximity of the poste rior a uxiliary deposits of the last cham ber of th e phragm oco ne. T he internal
d ia meter of the connecting ring from the body chamber is 149 5 !.I. m at th e d ista l end. 127 5 !.I. m in
the midd le a nd 11 90 :L m in the pro ximity of septa l neck. whereas the intern al dia meter of
siphona l tu be of the a nterio r section of the sipho n eq uals 1000 F m in the pr oxi mity of the
posterior a uxiIiar y deposits.
Th e last section of the siphonal tube situated in the body cha mber is not of unifo rm colour.
Light-br own o r yellowish at the d ista l end. it cha nges grad ua lly to a da rk-br ow n at the end of
septal neck. In a ll the rema ining cha mbers of the phragm ocon e the conn ectin g ring is uniforrn cly
dark -b row n in colour. da rker coloured than a nywhere in its final section.
G rowth lines are visible o n the dorsal pa rt of th e sectio n of the conn ectin g ring situated
in the bod y cha mber: they begin at the inner surface a nd run toward s its externa l surface in
distal di rect ion .
D ISC USS IO i" A i" () INT ERP R ETAT IO N
Studies o n the intern al structure of am mo nites. includ ing their septal necks. were car ried
o ut by HYATT ( ll0 2l. BRA\:CO (1880). G RA:'oJDJ EA\: ( 19 10). SCHIJ\: DEWOLF ( 193 1). BOII I\I ERS
( 1936). MILLER and U\: KLESBAY ( 1943) and others.
T he majo rity of these a utho rs discovered tran sition fro m rctroch oanitic septa l necks in
earl y stages to proch oan it ic necks d ur ing lat er gro wth. DRUZCZI C, BARSKOV and KHI AI\II ( 1968)
proposed a new term "a mphichoan itic septa l neck " fo r the tran sition al stage between the two
types of necks : the a mph ich oani tic septa l neck was sa id to be characte rized by two projecti on s
dir ected towar ds the poster ior a nd a nterior of the shell respecti vely, serving as the place of
attachment for the orga nic wall of the sipho n.
Ta king into acco unt the types of septa l necks present. a mmonites may be di vided int o
3 gro ups : (a) th ose with ret roc hoa nitic necks o nly. (b) those with rctro- and pr och oanitic
necks. a nd (c) a mmon ites with prochoa nitic neck s o nly. Th e first gro up co mprises mainly
Pal co zoic amm onit es. t he seco nd - Late Pal eo zoic a nd Early Mesozoic a mmo nites, and th e
third - o nly some repr esentati ves of the subo rde r Amrno nitina , for example the genera
Quenst edto ceras and Kosn ioccras covered by the present st udi es.
Previo us descript ions of the o ntogenet ic developm ent of septa l necks (HYATT. 1872;
BRA\:CO. I X80: G RA:"DJEi\01 . 191 0; SCHINDEWOLf. 1931: BOHM ERS, 1936: VOORTH UYSI'N, 1940;
MILLER a nd U:": KLESBt\ Y. 1943) were often fair ly extensive but . however, th e cha nges found
were not co mpa red with th ose known f r om R ecen t Na uti lus.
MUT VEI ( 1967: 16J) has given two possi ble inte rpre tat ions to am mo ni tes with ret rochoanitic
septa l necks.
( I) T he connect ing ring is ho mologou s with the co nchiolin layer of the connect ing ring of
Na utilus, o r
(2) the co nnecting ring is seco nda ry a nd. therefo re. not hom ologou s with that layer in Na utilus.
Acco rd ing to MUT\'EI (1967) a nd MUTVEJ a nd REYM EJ"T ( 1973) only a seco ndary co nnecting
ring is typical of ammo nites with proc hounitic septa l necks. DOGUZH AEVA (1973) reported
a tran sition from ret ro- a nd proch oan itic septal necks d uring the o ntog eny of Tr iassic
Megap hyllites a nd stated that "t he calcareou s circ umsiphona l tu be is atta ched to th e conn ecting
ring from the back is form ed a t th e expense of the retroc hoa nitic septa l neck . It is not exelud ed that similar tub es of earl y Cretaceo us phyllocer atid es a lso repre sent a hom ologue of
rerrochoanitic septa l necks. If thi s is suppo rted by S EM stud ies the similar ity in structure
108
CY PR JAN K ULl CKI
o f th e siphon of amm on ites and nauti loid s will a ppea r mu ch m o re im po rta nt th an M UTVEI
( 1967) assu me d" ( DOGUZ HAEVA, 1973).
A tran siti on fr om typi cal retro ch oanitic se pta l nec ks to proch oanit ic neck s via a tr an sit io na l stage was trac ed in th e o ntogeny of Nat horstites gibbosus STOLLEY.
Comparison of retrochoanitic septal necks of Natliorst ites , Nautilus and other nautiloids
Th e ret rochoa nitic se pta l neck of Natliorst ites, cha racte rized by a d ista l pa rt se para ted
f ro m th e remainin g pa rt s by a di scon t inuity (p I. 24 : 2, 3, 6, 7) a nd pa ssing int o th e wall of
the connect ing ring to wa rd s th e post eri or, ma y be co m pa red wit h t he retroch oanitic sep ta l
neck of Na util us described by M UTVEI ( 1972a) as we ll a s th o se o f fossi l o rt ho co ne nautil oid s
fro m th e Pcn sylvani an Buckh orn asp ha lt d escr ibed by M UTVE! ( 1972b) a nd RISTEDT ( 197 1).
Th e di st al pa rt of th e re trochoa nit ic septa l nec k of Na thorstites ma y be co m pa red with th e
"S ip ho w ulst" o f RISTEDT ( 197 1, pI. 37: 5; pl . 38: 1- 2, 7), the modifie d na cr eous la yer o f
M UTVEI ( 1972b, p I. 6: 1- 3 ; pI. 7: I ; pI. 11 : I ; fig. l A , B) a nd th e di st al m odifi ed nacreous
la yer of Recent Nautilus pomp ilius d esc ribed by M m -VEl ( 1972a, pI. 10: I ; figs. 2-3).
P roject ions a nd thi ck cnin gs of min eral ti ssu e fo un d a t the pla ce of a ttach me nt o f the a d apica l endi ngs o f co nnecti ng ri ng in Nat liors tites a rc interpret ed here as poorly d evel oped a ux ilia ry dep osit s corresp ondin g to th ose of Rece nt N autilus . The aux iliary d ep o sit s o f Na thorstites
gibbos us a ppea r to be less d evel oped in relat ion to the Recen t Na ut ilus figured by M UTVEI
( 1972a, fig. 2) .
Ontogenetic development of the septal neck of Nat hotstites
M UTVEI ( 1964 , 1972 a, h) ass ume d sy nc hro no us developme nt of the lamin a e of th e na creous
la yer in th e zo ne o f secretio n o f septa . St ud ies on th e she ll wa ll, of gast ro pods a nd biv al ves
carried o ut by W ISE a nd H AY ( 1968) a nd ERBE N ( 1972), ha ve shown th at sy nchro neo us g rowt h
p la nes a re o b liq ue in re latio n to la m ina e of nacr eous la yer. T he se pta sec re t ing zones of
ce pha lopods we re not cove red by s uc h st ud ies , bu t neverth eless, it ma y be taken th at thi s is
a lso th e case her e. Foll o wing th e views o f M UTVEI , the sec re to ry zo ne was o f ra pid ly flu ctu ating ex te nt. Fo r ex a m p le, th e who le a da p ica l s urface o f th e man tle, in clud ing th e la st sec t io n
of sip ho n , part icip at es in th e fo rm ati on o f th e ada p ica l orga n ic m embran e ( M UTVE I, 1964,
1972a, b) wh ilst, acco rd ing to M UTVEI ( 1972 a: 252), dur ing th e next sec re to ry ph a se, th e
co urse of th e g rowth la me llae in th e succeed ing na creous layer clearly de mo ns t ra tes th at th e
sp he r ulit ic-p risrna t ic la yer in th e septa l peri ph ery a nd sipho na l tu be form d uri ng the sa me
secreto ry ph a se. In co nse q ue nce , the su bseq ue nt sec re tory ph a se wo uld be ch aracterized by
a g rea t red uc tio n o f sec ret ing a rea, a nd th e s u bse q ue nt ph a se of sec ret io n of th e na cr eous
layer wo uld in vol ve, a s during th e in it ia l p hases. the whole a da p ica l sur fa ce o f th e mantl e.
Th e o bl iq ue co urse of sy nc h ro no us growt h plan es in re la t io n to lamin ae of th e na cr eous la yer,
as is th e ca se in th e she ll wa ll. suggests th at the st ruc t ura lly mo d ified nacreou s la yer shown
by M UTVEI ( 1972b) was secreted si m ulta neo usly wit h th e co nnect ing r ing . T he o bliq ue bound ary
(MUTVE I, 1972 h, pI. 7: I ; pl . 11: I ; fig . I A. B) is sy nc h ro neo us a nd mark s the end of the
p hase of sec ret io n of co n nec ting rin g a nd th e di sta l e nd of th e se pta l neck . If th e sec ret io n
of the di st al pa rt of the retro ch oaniti c neck did not end wit h e it he r a lon ger break or o t he r
a d di tio na l cha nge s, we are d eali ng he re wit h a p he nome no n of co nt in ua t io n o f lamina e o f
th e nacreous la yer bet ween str uc t ura lly m odified nac reou s la yer a nd typi cal nacreous layer
as em p has ized by M UTVEI ( 1972b, fig. 1 B) o r, as in th e first ca se , as it was em phasize d by
RISTEDT (1971 : 182) " bes te ht d el' Sip howulst a us prisrna tischen Schi chten . .. und wird vo n
ei ner Vielzahl von relative dicken Membran en durch zogen di e, wie a us F ig. 7 a uf Tar. 38 zu
ersehen ist , o ra l warts in der A pika len M embran des Septums zusam me n la ufen" .
TH E STRUCTURE AND DEVELOPM ENT OF AMMONITE SHELL
109
If follows that in ontogenetic development of the retrochoanitic septal neck of N athorstites
two pha ses of secretion may be distinguished .
(I) The first pha se of secretion, ending with formation of distal part of the retrochoanitic
neck, begins with formation of auxiliary depo sits on the inner surface of the preceding neck
and the adapical part of the connecting ring. The wall of the connecting ring , the distal part
of the septal neck and some section of the ad apic al organic membrane covering the septum
(fig. 2A ) ar e formed at the end of this phase of secretion. At that time the secretory zone is
presumabl y not much wider than the distal ending of the retrochoanitic septal neck, and is
separated from the rest of the neck by a discontinuity. The secretory zo ne is differentiated
into th ree subzones during the formati on of the adapical part of the septal neck: (a) that
secreting the organic cover of the sipho n; (b) that secreting the mineral tissue of the distal
endin g of the neck a nd (c) that secreting the adapical organic membrane of the septum.
(2) In the second pha se of secretion the remaining part of the neck and septum are form ed
(fig. 2 B). In the middle of that phase the secreto ry zone reache s its maximum extend, close
to that ass umed by MUTVEI (1964, I 972a , b), i.e. parall el to the laminae of the nacreou s tissue.
During thi s pha se, secretion is differentiated into two subzones at the most: (a) a subzone secreting nacreous tissue a nd (b) a subzo ne secreting the organic adapertural membrane.
Formation of prochoanitic septal necks in ammonites
BRA NCO (1880), BOHMERS (1936), VOORTHUYSEN (1940), MILLER and UNKLESBAY (1943)
and others found that the formation of a proch oanitic septal neck alway s starts at the ventral
side, extending subseq uently to cover the whole periphery of the retrochoanitic septa l neck.
Thi s often result s in the fact that prochoanitic septa l neck is already developed in the ventral
part when a retrochoanitic septal neck is st ill present in the dorsal part of the medial section
(BRANCO, 1880, pI. 9 : 9; pI. 11 : 9 ; VOORTH UYSEN, 1940, figs. 3,6). The phylogenetically
earliest a mmonites with procho anitic septa l necks are represented by some Late Carboniferous
Agathiceratidae displaying the transition from retr o- to proch oanitic septa l necks on the sixth
a nd seventh whorl s (DRUZCZI C et al. , 1976). Thi s tran sition is marked a t the fifth, fourth and
third whorls in Perrnian Go niatitina, as in Triassic representatives of the Order Phylloc eratida
prop osed by SCHI ND EWOLF (1968) and on the second and first whorl s of Jurassic and Cretaceous repre sentatives of Pliyllo ceras (see DRUZCZIC et aI., 1976). Similar examples of an accelerated transition between the two types of septa l necks in phylogeny are kn own in the
Lytocerat ina and Amm onitin a.
Ontogenetic growth of the connecting ring in the transitional phase in Nathorstites
In the transitional stage in Nat horst ites fo ur phases may be distingui shed:
( I) A phase correspondin g precisely to the first phase of form ati on of a rctr och oanitic
septal neck, in which the wall of the conn ecting ring and distal part of the equiva lent of the
retr och oanitic septa l neck are form ed (figs. 3A , 4 A). Differentiati on of the secreto ry zo ne is
as discussed above in the first stage of form ati on of the retr ochoan itic septa l neck.
(2) In the seco nd phase the subsequent pa rt of the equiva lent of the retroch oanitic septa l
neck forms. In this phase the secreto ry zo ne is also narrow, and differentiated into two subzo nes : (a ) the subzo ne secreting the nacreou s tissue and (b) the subzo ne secreting the conchiolin membrane covering the adapical surface of the septum (figs. 3 B, 4 B).
(3) In the third pha se the ada pica l part of the nacreous layer of the septum forms . The
adapica l boundary is repre sented by a discontinuity, whilst the adapertural boundary is hypothetical. and unmarked in the specimens studied . It is assumed that at this stage it is represented by a synchro neous boundary in relation to which the laminae of the nacreous layer
110
CYPR IAN KU Ll C K I
are a rra nged adapert urally, fo llowi ng th e patt ern ty pical of th e proch oa nitic septa l nec k.
The zo ne of secretio n is pr esuma bly very wide a t t his stage , a nd is ini tially di ffer ent iat ed into
two subzones, foll owed by uniform secretion of th e nacre ous tissue of th e septu m (figs. 4 C, 3 C ).
(4) In the fourth and fina l pha se, th e re ma ining part of th e sept um is formed . a s well as
the proch oani tic neck pro pe r. A stro ng forward s twist of th e lamin ae of th e nacr eou s tissue,
without a return towards th e ad ap ical par t indi cat es formati on o f a deep furro w sur ro undi ng
the ext en sion of soft sipho na l tiss ues in bod y cha mber durin g th is ph ase. Mo reover. secr et io n
of the a nterior a uxiliary dep osits a nd the con chi olin cover of th e sipho n is initi a ted. At the
end of this ph ase th e di stal endi ng of th e pr och oan itic pa rt of the septa l nec k beco mes co n-
o
E
F
G
'·"'·' i:·::,io::.\ \ ':">'. (. , ""':: :;-:<, <.,.,.; .,.C.. ,. •. •. ,.
.'
:'::' :' ;' :' : :"::'<:::'::~::':':\:' : : ::':'~:'~:":": -,:;:f', ::;' ..
Fig. 3
D evelopment of secretio n zones at va rio us stages o f format io n o f th e septa l neck a nd co nnect ing ring at the tra nsitory
stage in Nathorstites gibbosus. A-G - Successive deve lop menta l stages. a - Sipho nal mem bran es fo rmed after for ma tion of an adeq uate sectio n of co nnecti ng ring ; their organ ic tissue is discord an t relative to the orga nic tissue of the
co nnecting ri ng, or is ad ape rtura lly extende d into the external layer of con nect ing ring. b - Siphona l mem bra nes in
th e fo rm of a co ntinua tion of the exte rna l o rga nic layer of the con necti ng ring ; th ey a re exte nded ada pically, Yellow zo ne of secre tion of nacreou s tissue. R ed - zo ne of secretio n of co nchio lin of connecting ring from the interio r. Brown :-:
zo ne of secretio n of ada pertura l a nd ada pica l septum membran es; sipho na l membranes, a nd co nchio lin of co nnecting
ring from th e exte rior
T HE Sf R U CT U RE .-\1\ D DE V EL OPM EN T OF A M M ON ITE SHEL L
III
nected with th e co nnect ing rin g. An init ially uniform secretory zo ne fi nal ly d iffere nt iates into
two subzo nes: the on e secret ing nacreous tissue, t he o ther t he conchiolin mem b rane o f th e
adapertural sur face of the septu m (figs. 3 D E, 4 D) .
A rec onstructi o n o f sec reto ry zones ma kes it necessary to d isc uss t he rela t io nship of growth
surfaces to lam inae an d rod s of nacreou s ti ssue. TA YLOR et al. ( 1969) a nd E RI3EN ( 1972) have
sh ow n th at t her e are two types of nacreous tis sue, d iffe ri ng in t hei r mutu al a rra nge me nt of
p latelets: o ne, typical o f ga st ropods, ha s plate lets arra nged in so -ca lled stacks, a nd lam inae
are difficu lt to trace ; in the other, pla telet s do no t form stacks, a nd are a rra nge d in d istinct
la minae. In both cases synch ro no us planes a re set so mewha t o bliq ue to t he lamin ae of nacr eous
t issue .
The bulk of a m mo nites stud ied ha ve nacreo us tissue of th e first type. So me specime ns, a nd
esp ecia lly those re present ing early on toge netic stages disp lay parts of t he nacreou s layer with
F ig. 4
Diagra mmatic d rawin g o f the de velopmenta l stages o f the se pta l neck at the transito ry stage in Nathorstites gibbosus.
A -D : Th e late st developmen tal sta ges
poorl y developed stac ks. Lon gitudin al sect io ns of th e shell wa ll show th at laminae o f nacreous
tissu e a re nor parall el to th e exte rna l peri ostracal su rface but di verge at a sma ll a ng le to the
o uts ide in rel ati on to th e wh orl axis a nd directi on of gro wt h. In so me very ra re cases, when
th e course of gro wt h sur faces is visibl e (pI. 47 : 7), th e surfaces are deflect ed fro m t he whorl
ax is in th e sa me d irec tio n but at a so mew hat gr eater an gle.
Th e reco nst r uctio n of sec retory zo nes ba sed o n eithe r t he course o f gro wt h lin es o r the
ass umpt io n th at growth plan es are parall el to lam inae of t he na cr eous layer ( MUTVE I 1964,
1972a), is so mew hat erro neo us.
112
CYP R IAN K ULlCK I
La m inae of th e nacreous layer are no t inc lined to th e ada pica l surface o f th e se pt u m in
th e case o f amm onites stud ied her e. G ro wt h planes are not visi ble o n th e surface o f th e se pt u m,
nor in cross-sec tions. So-c all ed di scontinu ities, visib le on d irect repl icas of Na thors tites gibbosus
as d ep ression s, a nd th us simila r to the rem a ining o rga nic memb ran es or o rga nic r ich areas,
see m to be th e exce pt io n her e. Disconti nuities are a lso marked by a break o n th e ada pica l
sur face o f th e se ptu m in Nathorstites . It see ms, th er efore. th a t d iscon t in uit ies di spla yed by
Na thorstites d o not re p rese nt bound aries between lamin ae of nac reous tissue, but ra t he r
synch ro no us gr owth pla nes se pa ra t ing su ccessive p hases o f secret io n. In th e case o f se pta
g rowth plan es may be para lle l to lamin ae o f nacreou s t issu e as shown in dra win gs a nd desc riptio ns given by M UT VEl ( 1964, I 972a) .
On th e sectio n throu gh septu m , septa l neck a nd sipho n of Eleg anticeras elegantulum give n
by M UT VEI (1975. fig. 2). we not e a da rk boundary pa ssing th rough t he middle a nd a pp roac hing ad api cal surfa ce of th e se ptu m in th e pr oxim al p a rt of the neck. Thi s bound ary corresp onds
to the di scontinuities see n in Na tho rstites, se pa ra ting th e olde r part o f th e sept um fr om th e
yo unger part and th e se pta l neck.
Th e development o f sec re to ry zo nes during th e tran siti on from retro- to pr och oanitic
sta ges is illu strated in fig. 3 A- G. Three typ es of sec ret io n a re di stinguish ed:
(I ) secretion of nacreou s tissu e (yell ow), (2 ) secre tio n o f th e conchi olin o f th e connecting
ring from within (red), a nd (3) sec re tio n of th e ad a p ica l a nd adape rtu ra l se pta l membran es,
s ip ho na l membranes a nd th e co nchio lin o f th e co nnecti ng rin g fr om th e o uts ide (brow n) .
Ontogeny of the prochoanitic septal neck of Na thorstites
Some laminae of th e p oster io r a ux ilia ry d ep osits ma y o r igm ate a sy nc hr o no us ly to th o se
o f th e septa l neck a nd sept um . T hey d o not rep resent a mo rphologica l extensio n o f neck a nd
se ptu m as was th e case in th e retrochoa nitic septa l nec k (see fig. 5). A na lysis of th e tr an sit ion a l
stage o f growt h o f Na thorstites has shown a ret a rdati on in th e fina l formati on o f th e pr och o a nitic part of th e neck in relat ion to th e poste rior a uxi liary dep o sits. Simila r re tarda t io n ma y
~- ··-~--=~=~~~;~~~~~r~:¥~~~
I----_~
--
-
Fig . 5
D ia gramma tic d rawi ng of a prochoa nitic se pta l
nec k in Nathors titcs gib bosus
_= =--;; :~j!=- --
~
be inferred in t he ca se o f th e ea rly stages o f occurrence o f p rochoa nit ic septa l neck s. In lat e r
g rowt h stages it is equ a lly pr obab le t hat t here is both ret a rdati on a nd accelera t io n in forma tion
of septa l neck and septum in re lati o n to th e posteri or auxi lia ry deposit s a nd th e sipho n.
Ontogeny of septal necks and auxiliary deposit s in Qu enst edtoceras and Kostnoceras
T he mai n d ifference in the o nto ge ny o f Quenst edt oceras a nd Kosn ioceras is in the pos itio n
of the siphon in the seco nd se ptu m : in Kosmoceras it occu p ies a ce nt ra l positio n and in Quellstedt oceras it lies a t the ve ntral margin . Th e o ntogenct ic development o f se pta l necks and auxiliary dep osit s is th e sa me in bo th gen er a .
THE STRUCTUR E AND DEVE LOPMENT OF AMMONITE SHELL
113
The first on e, two . or even three septa are ac hoanitic, th at .is without a septa l neck ; a p ro-
c hoanitic septa l neck first a ppea rs on subse q uent septa. A s a rul e, it is initially better developed
on th e vent ra l side. but thi s differ en ce in d evelopment soo n di sappears. In some specime ns
of Quenst ed toceras th e dep osit s occur ring between the ad a pe rtura l surface and the wall o f
th e conn ect ing ring o f th e seco nd sept um may b e trea te d as the d istal part of a prochoanitic
septal neck. Th e tran siti on al stage fr om ac hoa nitic neck s to o ne of a m arked difference in
developmen t of ventral a nd d orsal pa rt s o f septa l necks comp rises fr om one t o more than
three who rls, and the fully develop ed proch oanitic septa l neck s which appear su bseque nt ly
are re tai ned to maturi ty.
Poster ior and anterior a ux ilia ry de pos its are well d eveloped throughout the ontoge ny o f
both Quenstedt oceras a nd Kosmo ceras , but t he latter a re usu all y not developed on the ventral
part of the proseptum .
ERBEN et al. (1969 , p l. 16 : 4) misinterpreted a nte r io r a ux ilia ry deposits from the dorsal
part o f the proseptum o f Quenst edt oceras as a seco nd se ptum . Commonly with the second
septurn in Kosinoceras a nd th e third in Quenstedtoceras, a nter ior and posteri or auxil iary
deposits occur regul arly, the latter usually being the better d eveloped.
Juvenile an d mature specime ns of Quenst edt ocera s with body chamber preserv ed displa y
posterior a ux ilia ry deposit s and , so metimes, a nterio r a u xilia ry deposit s, alt ho ug h poorly
devel oped o n th e la st sep t um. Posteri o r au xilia ry d eposit s fr om the la st septu m a re al so known
from severa l ot he r a mmo n ite ge nera including Cadoceras , Polyptychites, Craspedit es, Aconeceras, Saynoceras , Kosm oceras a nd Holcopliylloceras a nd a nte rior o nes from the genera Holcophylloceras a nd Craspedites.
The last formed section of the siphon
The stu d ies carr ied out by TRUEMAN (1920) a nd W ESTERMANN (1971) have shown that the
sip ho n is not usually pr esent in the ch ambers o f the last whorl o f phragmocone. It is visible
in th e la st ch amber o f the phragmoc one o nly in the case of exc eptionally well-preserved material (verbal communicati on s by R EYM ENT, HOLD ER a nd WIEDMANN in: WESTERMANN, 1971).
This is ex plained by M UTV EI (1967 , 1973) a nd W ESTERMANN (1971 ) as a re sult of retardation
in d evelopment of th e connecting rings in comparison to septa a nd septal necks:
DRUZCZIC a nd DOGUZHAEVA (19 74) fir st de scribed and figured a sipho n developed in the
la st c ha m bers o f the phragm oc on e and b od y chamber of Phyllopachy ceras sp . ; the siphon
sectio n from th e body chamber o f that specime n is twice the length of th at in the last chamber
o f th e phragm oc on e. Th e specime n o f Ho lcopliyllocera s sp . de scribed above (see p. 14) is the
seco nd known with siphu ncle preserved in th e b ody ch amber, a lt ho ug h in thi s case the siph on
sectio n from th e bod y cha mber is sho rter than th at fr om the la st ch amber of phragmocone.
Both these specimens are member s o f th e Ph ylloceratina , a group characterized by a sip h uncu lar
tube with a much high er stre ng t h ind ex than th at found in th e Amm on itin a , and clo ser to that
of N autilus (see W ESTERM ANN, 1971 : 25). The specimens of Kosm oceras and Qu enstedtoceras
from Luk 6w d o not ha ve the siph unc le p reserved in eithe r th e last c ha m be rs of th e phragmocone
or in the body cha m be r. N everth eless, the presence of posterio r a uxilia ry dep osit s a nd, so me times, a nte rio r o nes indicat e its former prese nce in these la st chamber s and even in the body
chamber.
The last septa l neck of a juvenil e Quenst edtoceras is illust ra te d in plate 33 : 2. A zo ne o f
channels, made by boring o rga nis ms a nd subseq ue nt ly infilled with pyrite, is found in parts
of th e sept um wh er e anterio r a nd p o steri o r a ux iliary d ep o sit s sho u ld occ ur. The subs tra tu m
in which the b oring organi sm lived wa s eit her removed during prep aration by decalcification
in E D T A or by di agen etic processes. The thickn ess o f the zo ne with borings im plies a remarkable thickn ess of th e subs trat um. The zo ne of infill ed borgins is limi te d a nd p osterior
a ux ilia ry d ep osits a re partl y ca lcified o n th e penultimat e sept um (pI. 34: 4). The septu m third
from the rea r has calcified a ux ilia ry dep o sits with no trac es of borings on them (pI. 34: 3).
3-
Pala eon tolog ia Polonic a No . 39
11 4
CYPRIAN
K ULlCKI
T he last three scpra of other ju ven ile rep rescn t.u ivcs of Q uen vtedtoccras ltenrici (sce pI. 32 : 3 ;
pl. 33 : 1. 3, 4) d isp lay fully develo ped a uxiliary deposits wit ho ut any traces of boring or ga nis ms.
T he last sept um shows fully develo ped poster io r a uxilia ry de pos its exte ndi ng fro m the d ista l
end of th e septa l neck a nd prot rud ing som e dista nce ba ckward s. Th e a uxilia ry deposit is here
stro ngly calcified , except fo r that part adj oi ning the siphona l open ing. wh ich is ch arac ter ized
by free spaces indica ting t ha t they were origina lly inlillcd wit h so mewha t di fferen t ma terial
(pI. 32: 3). T he penultimat e scp t um ha s cal cifi ed po ste rior a uxilia ry dep os its a nd poorly de velo ped, pa rtly ca lcified a nterior a uxilia ry dep osit s with free spaces in their front a l pa rt (pl. 33 : 3).
Normally develop ed a nd ca lcined posteri or and a nte rior au xilia ry de posi ts do not appea r befo re
th e septum th ird from th e rear of the body cham ber (pl, 33 : 1. 4).
Interpretation and conclusions
In Q uenstedto cerus an d ot her a m mo nite genera th e pos te rior a uxi Iiary deposits, rep rescn ting the adape rt ura l end ing of th e con necting ring. ar c as a rule better develope d than the a nterior dep osits of th e sa me co nnecting rin g, a lth ough the a nte rior aux ilia ry de posits origina te
ear lier th an the posterior of th e sa me connecti ng ring. T he presence of posterior au xilia ry
deposits o n the last sept um sepa rating th e bod y cha mber a nd phrag moco ne, ind icat es th e
presence of a co nnecting ring in th e 111st cha mber of the phragmo co ne. Th e presence o f free
spaces in th e zo ne of grow th of th e auxilia ry de posits of the last two septa , resulting fro m
eit her post-diagen etic processes o r etc h ing in ED TA, ind icate the prese nce of mineral or or ga nic tissu es in th ese places which differed from bo th no rm a l calci fied po sterior a nd a nterio r
aux ilia ry deposits a nd the o rga nic tissue of the conn ecting ring. T his is furth er supported by
a series of microg raph s of th e last two sepi a. wh ich reveal t hat on ly certai n par ts of the au xiliar y de pos its from the penult imat e septurn were exposed to t he action of bor ing o rgan isms.
A fairly wide zo ne of borings from the ultima te sept um indicates th at th e substrat um wa s
o rigina lly very thick. Posterior and a nterior a uxiliary depos its of the th ird or fo urt h scpt um
countin g fro m the body chamber in Quenstedto ceras ar e fully developed wh ilst the conn ectin g:
ring is often not p reserved fo r a greater dista nce.
It follo ws f rom the a bove dat a . as well as thos e given by TRUEMAN (1920) a nd W l ST LRMANN ( 1971), that th e last section of sipho n is usually not pres er ved fo r a di sta nce of a bo ut
one who rl. T his im plies th at t he last section of sipho n of th e A mmonitina is lack ing beca use
of bot h a reducti on in thickn ess o f the co nnecting ring (MUTViI. 1967, 1973) a nd post-secreto ry
pr ocesses (maturation) affect ing th e orga nic mat ter of th e t ube. Dark matter resemb ling th a t
formin g th e co nnecting ring is visible under t he light m icroscope on th e septal neck of the
la st septu rn o f Kosm oceras and Quenst edt ocerus with preserved bod y cha mbe r in th e positi on
where a uxilia ry deposits should occ ur .
T he post-secretory changes (mat urat ion) seem also to be ind icat ed by d iffe rence s in co lo ur
an d di stribution of gro wth lines on th e sectio n of sipho na l tube describ ed from th e bod y
ch amber of Holcophylloceras zignodianutn.
The post-secretory ch anges in the o rgani c matt er o f t he co nnecting ri ng pr oceed at a distance of a bo ut a wh orl o r mor e in imm a ture Quenst edt oceras, a nd a bo ut a half of whorl in
ad u lt one s.
The connecting ring a nd a uxilia ry dep osits a ppear independe ntly of th e prochoanit ic neck,
and it is po ssible th at th e connecting ring is for med ear lier tha n the success ive sept um a nd
its prochoanitic septa l neck , as is th e case in H. z ign odianuni fig ured here a nd in th e Pliyllopachyceras sp. described by Dnu z c zrc a nd DOGUZHA EVA ( 1974).
The analysis of the development of posteri or a nd a nterior auxiliary deposit s from th e
last septum of specimens of Quenstedt oceras mad e it possible to assu me th at a sipho nal tube
was present in the body ch amber of th ese represe nta tives of th e Amrn onitina as it was in the
Phylloceratina.
T HE
STRUCT URE
A
O[)
D E VE LO P:'-IE T OF AM MON ITE S HE LL
115
Accor d ing to ;'VIUI\I I (1972(/. 11 ) the cochio lin layer or the con necting ring or Recent Nautilus represe nts a d irect contin uat ion or the nac reous layer or the septa l neck. from whic h it
d iflcrs in being uncalciticd . T hese two zo nes o r secretion were in action synchro nco usly during
the Iormution o r the scptum a nd the co nnecting ring, T he action of the se secreto ry zo nes
grad ua lly became asynchronou s durin g the forma tion o r pr oc hou nitic septal neck. Fro m
a theoret ica l viewpoint. asynchronous secret io n of septa l neck a nd con nec ting ring may
result in:
(I) accelera tio n or reta rda tio n in the for mat ion of the sipho na l wall to the last scpturn ;
(2) the possibility of form.uion (\1' the wall of the connecting ring from both inside a nd o utside,
when a deep furrow i:- produced in the poster ior pa rt o f the bod y. i. e. in the case when for mat ion of the co nnecting ring is accelera ted:
(3) the possibility of co nnectio n of the externa l surface o f the connecting ring to the surfaces
or both the scptum and the ventra l wall or the shell via auxi liary structures such as sipho na l
mc mh ran cs :
(4) the possib ility of stcpwisc moveme nt of the posteri o r part of the body to the site o f for mati on o f successive septu. preceded by the form a tion of the soft tissues of the sipho n. Th e
furr ow from the posterior part of the bod y was deepest before trans location a nd shallowest
after tra nslocat ion. as a resu lt of parti al 1)1' comp lete inversion o f the secreting tissuc .
" 'ilh "('/<'/'('11 ('(' 10 po int ( / ) . Murvrt (1973: 629 : ass umed that the form ati on of the sipho nal
tube was so mewhat accelera ted in relat ion to the fo rmati on of the last scptum. Th e "primary
memb ra ne" is the first clement origina ting o r the sipho na l tube . an d it represen ts a direct
exten sion of the mcrnbrunc covering the externa l surface o f the neck . being connected with
the adap ica l co nch iolin membran e o f the following scptum (MUTVEI . 1973 : 29).
/Vi lh /'(:/;',.('1/('(' 10 point (2). the following da ta co ntradic t MUTVU'S ( 1973) co ncep t of a prima ry mem bra ne: the section of the sipho n ori ginating in the bod y cha mber is lon ger th an the
inte r-septal distance (see f)RUZCZIC and I)O(itJl.IIAFVA. 1974. fig. 2) a nd the septa l neck s have
distal ends rising ab ove: the sipho nul surface a nd not co nnected with it by orga nic membra nes
(pl, 30 : -1: pl. 32 : I ). Membran es co nnec ting the d istal ends of pr och oani tic neck s with the
surface o f the connect ing ring cor respon d in character to the sipho naJ me mbra nes co nnecting
the adupcrturu l septal sur face and co nnec ting ring,
G rowth lines fro m the walls of the sipho nul tube of l t olcophylloceras descr ibed here (p. 14)
ind icate secretion of the tube from within . whilst illustrati on s o f the sipho n of Lytoceras ju"('I/ I'C . given by (i R,,'I>J I A' (1910. figs. 4 5) ind icate a t least partial secretion from the o utside.
In all prob abi lity secretion from both within a nd witho ut were involved in the formatio n o f
th e co n nec t i ng rill ,!!,
/I 'i l h rcicrcnc« 10 point (3 ). Amm onites are characterized by the pre sence o f so-ca lled
siph on u] membran es. viz. org a nic struc tures co nnec tin g the sipho na l surface to other elements
of the she ll. No such orga nic fi lms ha ve: been found in represent ati ves o r the Nautiloidea, but
organic films in .unmonoids were descri bed or illustra ted by severa l a utho rs includ ing GRA'f)JI , \:-" (1 910). SlIljl.(;,I-NI SII Ri' KIl (/ 92(1 ). MII.I.IR a nd
'K I.lSIlAY ( 1943). H OLDER (1954).
SCIII ' I> I \\() I. F ( 1%7). WISII R\lAV, ( 197 1), a nd ERIlI:-" an d Ru n (1 97 1), Well-devel op ed
memb ran es from the st:lge or rctroc hoan itic septa l necks o f , fga l hic('l'l/ s IIra !iCl II I/ were describcd by SIIlJI.(; A-NISILRI :-: KIl (1926) o nly. whilst i\'111.UR a nd U~ K I.I :S Il A Y ( 1943) descri bed
poo rly develo ped sipho na l mem bran es from both the rctr o- and prochounitic septa l neck
stage s in Late Palcozoic ummono ids. Ot her a uthor s described siphona l mem bran es or a mmonit es a t the stage o r proch oan itic septa l neck s.
Th e stud ies carried o ut by the pre sent a utho r o n Permian and Dcvo nia n amm oni tes from
his 0\\'11 co llections a nd those o r SlIl·i.(;A-NLSII:IU "KO and BO(;OSI.O\,SKAYA sho w that sip ho na l
membr an es arc very rare in Pa lcozo ic am mo nites. beco ming comm on and var iou sly deve loped
in Mcsozoic form s. Fig.3G shows the scheme o f formati on of sipho na l mem bra nes
postu lated for the stage of tran sition al septa l neck s. It follows that two types of siphona l
11 6
CY PR I :\ ;--i K ULI CKI
m emb ran es may be d isti ng uished, taki ng int o acco un t th eir relatio n to the co nnecti ng ring :
(a) sip ho na l membran es formed after the fo rmation of th e a pp ropriate section of co nnecting
ring, with orga nic tissue located d isco rda ntly in relatio n to th at of the connecting ring, or
extending into the external layer of t he con nect ing ring in a n adapertural direction (fig. 3 G a) ;
. (b) sipho nal membranes represent ing an exte nsion of th e exte rnal orga nic layer of th e connecting ring in a n ada pica l di recti on (fig. 3 G b).
Fro m a theoretical sta ndpoi nt, th e co nnecting ring equivalen ts in length to th e di stance
to th e next septum may originat e in th e bod y cha mber of bot h retro - a nd prochoanitic forms,
which permits formation of siphona l membran es as noted a bove. In the case of Phyllopacltyceras sp. (see DRUZCZI C and DOGU ZH AEVA, 1974) in which the section of the sipho nal tube
from th e body ch amber was longer than th e dista nce between success ive septa, o nly pr och oanitic sept al neck s may develop whilst siphon al membranes may orig ina te only when the
condition (b) is fulfilled.
Siphon al membrane s a re comm on in all bu t th e first or first a nd seco nd wh orls of th e
Ammonitina (WEST ERMANN , 1971), impl ying th at case (b) is more favourable for formation
of these membranes, as well as th eir connections with connecting ring.
With reference to point (4). The relati on ship bet ween movement of t he bod y inside th e
body chamber of R ecent Na utilus and selectio n of th e place of formati on of a new sept um
and formation of new section of soft siphonal tissues rem ain unkn own .
From th e the oretical point of view two extreme situa tions may be expected : (a) when th e
b ody moves relatively slowly to wards th e place of fo rma tion of a new septum , a nd a n increase
of siphona l length takes place in th e growth zo ne, a nd (b) when the body moves relatively
qui ckly towards th e place of formati on of a new septum a nd t here is di sten sion of both the
siphon and th e posteri or pa rt of th e bod y, wh ich is co mpensated subseque ntly during th e
followin g pau se.
The form ati on of a sipho na l tube in th e body ch amber of a n a mmonite, presuma bly befor e
m ovem ent of th e bod y to th e place of formation of a subseq uent sept um, may serve as a n
adapta tio n to the "s tepwise" nature of th e movemen t. Thi s co ncept seems su ppo rted by the
fact that " Siphos tru ktur" a nd " M uske la nsatz-St rukturen" inter preted as mu scle sca rs by
J ORD AN (1968) a re metamer ic, a nd correlat ed with th e septal rh ythm . It would ind icat e th at
th ey reflect per iod s of stationa ry muscles attac hme nt whilst a da rk band connecting them
wo uld mark th e track of th e mu scles b etween suc h pa uses .
Dnu zc zrc et al . (1976, fi g. 6) present ed a scheme of tr an siti on from ret roch oani tic septa l
necks in the onto geny of M egapliyllites pronieteus, a rep resent at ive of th e sa me superfamily
as the Natliors tites gibbosus stud ied here, th e Arces ta ceae MOJSISOVICS, 1875 in which th e
int ermediate stage is the retrochoanitic septa l neck . The proximal pa rt of thi s neck is stro ngly
bent ada perturally alo ng with the septu m, which is visible as a fold o n the cr oss-secti on
(ibidem , fig. 6b). Studies on the tr an siti on from retrochoani tic to pr och oanitic septa l neck s
in Na thors tites gibbosus failed to confirm th e necessity of occurrence of such a sta ge. The development of an ada pertura l bend in t he pr oxim al part of septa l neck a nd sept um is o nly
slightly related to th e m ost imp ortant pr ocesses active in t he secre to ry zon es during the tr ansitional stages.
EMBRYO NI C SH ELL
OBSER VATI ON S
The structure of the initial chamber and the first whorl up to the end of nepionic swelling in
Kosmoceras and Quenstedto cera s
Initial chamber. - The wall between th e initial cha mber a nd th e first whorl is built of
several layers, including organic films. Its a p ical a nd dorsal parts are two-layered and the
TH E STR UCT UR E AND DEVELOP MENT OF AMMON IT E SH ELL
117
ce nt ra l part four-la yere d . T he increase in number of la yers to four is achieved by ad d itio n
of two layers fro m with in (pl . 44 : 3; figs. 6, 7). T he t ot al thic kness of the wall of the init ial cham be r
is variable, being the greatest in the pro xim ity of the a ttach ment o f th e ve nt ra l pa rt of th e
p roseptu m (9-16 [1. m, on the ave rage 12 urn) a nd th e lea st in a pical a nd d o rsal parts (4-5 p. m).
The inner la yer present in apical a nd d orsal parts of the initial chambe r represe nts the
wall proper a nd is bui lt of regu la r prisms o f prismatic tissue (pl . 44 : 3- 1c; pl, 38: I b- I a).
Fig. 6
Media n section thr ou gh th e initia l cha mber a nd first wh o rl
of Quenstedtoc eras (diagram ma tic drawing of a large
phragrnocone)
It is 2-2'5 :1I11 th ick in t hese pa rts of the initi al cham be r. Small tubercles, di rect ed to the
out side , and formed by ex te nsions of prism s (p l. 38 : I b-l a) are visib le in cr o ss-secti on s in
th e proximity of the a ttach me nt site of the proseptu m a nd the seco nd septum. The tubercles
a re so metimes ch aracter ized by a sphe ru litic structur e.
T he inn er la yer , t ha t is the wall proper of th e init ial ch amber, is thickest 3-4-3 '6 p .m thick)
in th e proximit y of th e caec um a nd prosiph on , in the ven tra l part o f th e ch amber. The wall
p ro per of th e in itial c hamber is markedl y red uce d in thickness, wed ging o ut completely. The
la yer ex te nds contin uou sly a s th e ex te rnal layer o f t he firs t whorl, bein g cover ed only by dorsal
wa ll of th e next who rl.
T he ex te rnal lay er o f the initial c ha m ber represents the d orsal wall of t]le fir st whorl a nd
is, th er efore, di scu ssed with it. In the ventral pa rt o f th e first whorl there .11 e also two other
layer s: an in;ternal layer with o bvio us pri smatic str ucture (pI. 44: 3), a me ." very thin and
a lso pri sm atic laye r which is a lways much m ore markedl y effected by etching t 'In other layers,
.,
a nd is built o f much thii r pri sm s.
The prisma tic m icrosti et urc of th is la yer beco mes o blitera ted, so meti mes co m plete ly, a nd
beco me s more rand om in places where it is situ a ted at th e base o f th e prose pt urn nea r th e
ve ntra l wa ll a nd th e swe lling o f medi al la yer (pl, 38 : I a; pl, 28 : I. 2; p l. 3 1: I).
Th e in itia l ch amber is se pa ra ted fro m th e first who rl by th e proseptum , i. e. the first septu m .
Th e re lat io ns bet ween the proseptum, th e wa lls a nd th e init ial cha m ber a nd th e first who rl
have been di scu ssed elsew here ( K ULICKI, 1975). It was found th a t , d ep endin g on o rienta tio n
of the two cross-sec t io ns . th e pri sm atic la yer o f th e pr o septum passed smoot hly int o th e
prismat ic tiss ue of eithe r th e pri sm ati c layer o f th e initi al c ha m be r o f ve ntra l part o f the first
who r l (pl, 29 : 1,2 ; pl. 30: 2; pI. 3 1: I ; pl . 38 : I a; pl, 42: 3; pl. 44: 3). Some sections pa ssin g
throu gh th e lat er al part of th e initia l cha m be r d ispl ay a di scordant a rra nge me nt o f pri smatic
proseptum ti ssue in rela tio n to tha t of the initi al ch amber a nd wh orl (pl , 42 : 2).
Th e medial layer forms a swelling a n terio r to th e ba se of the pr oseptum in medi al a nd
pararnedi al sect io ns on th e ventra l sid e. Secti on s passing through th e lateral part of the initial
11 8
CYPRIA
T
K UUCKI
chamb er a nd prosept um display a media l layer of normal thickness (p l, 42 : 3, 4) o r none
(pI. 42: 2).
Th e wall of th e initial cha mb er ends with a flan ge in the dor sal pa rt in medi al a nd paramedial sections (p is. 28: 3; pl, 30 : I ; pl. 31: 2 ; pl. 39 : 3 ; fig. 6). T he fla nge is separated fro m
A
Fig. 7
Ontogenetic development of the initia l chamber a nd first whorl as illustrated by Quenstedtoceras. Red - secretion of the
wall pro per of the initia l chamber , externa l prismat ic layer of first whorl, a nd the o uter prismat ic layer of the postembryonic shell; yellow - secretion of the mid-layer of initia l chamber a nd flange ; inner pr ismatic layer of initia l chamber
a nd first whorl ; prismatic-sub prismatic mid-layer of first whorl ; a nd nacreo us layer of nepionic swelling and postembryonic shell ; brown - secretion of outer comp onent of dorsal wall; gre en - secretion of inner pr ismat ic layer ; blue secretion of nacreous tissue of septa . A-E - Successive phases of the shell format ion a t embryonic stage. F - Early
postembryonic stage
TH E STR UCT UR E AN D D EVELOPMENT OF AMMONITE SH ELL
119
th e wa ll o f t he in itia l chamber by a d iscon tin uity (fig. 6). Its minera l tissu e is usu all y less regular
an d severa l times t hicker tha n that o f th e wa ll p roper of the initial cha m ber. The flange does
no t occur in sectio ns passin g th rough the la teral part of t he ini tia l cham be r, as it is separated
fro m its wall by a d isco nt in uit y (pI. 29 : 3 ; pI. 42 : I). In such cases it is possible to detect
swelling o n th e d istal end o f t he wall of th e ini tial cha mbe r. The flange a nd the end o f dorsal
wa ll of the in itial chamber a p pea r t o hav e a n un even , h umm ock y margin when see n fro m the
inside o f the ch amber (pI. 26 : I, 3 a ). T he rela tion ship bet ween th e pro septum a nd th e wall
o f the initi al c ha mbe r were d isc ussed in part in a n ea rlier p ublica tio n by th e a u tho r ( KULICKI,
1975). In th at part o f th e pr oscp tu m which sho ws a well-dev eloped mural sectio n sa pa ra ted
fr om th e wa ll of th e init ial cha mber by a d isco nt inuity which gr aduall y di sappears in the
ad apert ura l d irecti o n (pI. 28 : 3; pI. 30 : I ; pI. 36 : 3; pI. 39 : 3).
The firs t whorl, - Th e wa ll bet ween th e first a nd t he seco nd wh orl co nsists of 4 main
layer s:
( I ) th e most external , d orsal wall of the s ubse q uent whorl ;
(2) th e exte rn a l prismat ic lay er of the first whorl , representing a direct extensi o n of the wall
pr o per o f the initial ch amber und erl ying th e d orsal wall of th e subseq uent whorl. After a redu cti on of thickn ess fr om th e tran siti on fro m th e wall of the initial ch amber to the wall of
th e first whorl t he wall is 1'3-2 fUTI thick (1'65 fL m thick o n th e average). The thickness of
th a t layer eq ua ls 1- 2 [1.m ( I -46 fL m o n th e aver age) in th e pr oximity of the nepionic swelling.
Th e min eral ti ssue a nd o rna menta t io n of th at layer were described a bove a lo ng with the initial
chamber ;
(3) th e med ia l p rism a tic layer of th e first who rl, occ urri ng beneath the ex te rnal pri sm atic layer ,
is characterized by a ma r ked t hickeni ng in th e pr oximity o f th e seco nd sept um , being 4'2-7 fL ID
in th ick ness (6,1 fLm o n the a verage) in th e proxim ity of the seco nd se ptum a nd 6' 5- 9'7 [).m
(7·R :.Lm o n t he avera ge) close to the nepion ic swelling. The min eral tissu e o f th is layer is
characterized by a prismat ic st r uct ure which u sua lly is, how ever, less regular th an th at of the
layer (2) a nd is ter med sub prisma tic. Its str uctu re is di fferentiat ed into a n external part which
is usu all y less regu lar, a nd built o f m o re regul ar prisms th an t he internal part (pI. 38: I b, I a) ;
(4 ) t he intern a l prisma t ic layer , re p resenting th e most int ern al mineral co mpo nent o f the
ventra l wa ll of th e first who rl ( fig. 6). The intern a l prisma tic layer is clearl y separated from
th e med ial pri smat ic layer o f the first wh orl , a nd lirst a ppea rs between th e fourth a nd fifth
scptu (pl. 43 : I b). A nal ysis o f t he boun dary bet ween th e seco nd sept um and ventra l wall has
sho wn th a t it is sha rp o nly in th e posteri or part. It di sappears toward s the a nterior but its
exte nsio n is mark ed as a co nstrict ion o n etched pri sm s o f th e prismat ic layer (pI. 28 : 2: pI. 38: 1b;
pI. 39: I: tig. 8). Th e furth er exte ns io n of th e boundary cuts normal-size pri sm s without any
traces o f gro wth d isco nt in uities. a nd it a p pears th at th e growth of prism s took place after
mo vem ent of the bod y forwa rd s, whi lst mo vem ent wa s not connect ed with a ny break in growth
o f pri sm s.
Taking into acco unt th e relation ship between th e seco nd sep t um a nd the ventra l wall,
it is necessary to ass u me th at th e inte rnal p risma tic layer continues on th e ventra l side from
dw
Dull.1
mU
lUJll--ill.1l±~~~~ ~~~'t«tttmt
Fig. 8
Median section thr ough the ventral wall in the proximit y of the attachment of the second septum
t
120
CY P I{IA N K U LIC K I
the seco nd sep tum o nwa rd s. It is 1·2 to 2 :J.ln thick (1 ,63 :: m thick on the ave rage) on th e first
whorl. Th e ti ssu e of the inte rnal pris ma tic layer of t he first who rl is regul a rly prismat ic.
The d orsal wa ll of the firs t whor l re prese nts the mo st exte rna l compone nt of the wall o f
the init ial cham be r. A we ll-develo ped m ur al part of t he prosept um (p I. 28 : 3; p I. 29: 3;
p I. 30: I ; pI. 31 : 2 ; pI. 36: 1,3 ; p I. 39: 3; p I. 42 : I) origina tes as a first cleme nt o f thi s wa ll.
A b ound ary se para t ing th e mural part o f th e prosept um fr om the wa ll p rope r o f the in it ia l
chamber gradually di sappears toward s th e apert ure un der th e mura l part o f the successive
septu rn (the third se ptu m in Quens te dtoc eras a nd seco nd se pt um in Kostn oceras] . A si m ilar
situatio n is found in th e case of subseq ue nt sep ta. Exce pt for th e ap ica l part of th e initia l
chamber, the su b pr isma tic tissu e of th e exte rnal co m po ne nt of the d o rsal wa ll o f th e fi rst
whorl a ppea rs b etween th e mural pa rt s o f t he septa a nd th e wa ll p roper o f th e initial ch a mb er,
an d di sappears in th e pr oximity of th e pro siph on a nd caecum (pI. 42: 4 ; pl, 43: I a; pI. 44: 3).
The d orsal wa ll of th e first who rl is 2·2-3 ·0 fL m thi c k (2,7 [1-m thi ck o n th e a ve rage) in t he
apical- vent ral part of th e in itial chamber. The b oundary bet ween the d o rsal wa ll of t he first
whorl a nd th e ex te rnal wall proper of the initial chambe r is no t sha rp.
Th e t hickness of the d o rsal wall d ecr eases to 1·3-1 '5 [1-m in t he p ro ximity o f th e a ttac h me nt
o f prosiphon a nd cae cu m . The prism atic struc ture of wall is we ll-marked he re, and th e wa ll
is separa ted from the shell by a clearl y ma rked d isco ntin uity (pI. 28: I ; pI. 30: 2; pl . 44: 3 ;
pI. 38: 1 b , I a : pI. 42: 3, 4 ; p I. 43 : I a). A c ha nge in dorsal wa ll t hick ness in th e pro ximi ty
o f th e a ttach me nt of th e pro sip h on a nd caecu m co rres pond s to cha nge s in shell str uct ure
which origina te at th e nepi onic swelling. T he sect ion tran sverse to t he bo dy chamber a nd
the fir st wh orl sh ows that the m ost exte rnal layer o f th e d o rsal wa ll in rela tio n t o the first
whorl (the external component of the dorsal wa ll) passes o n the ex te rnal side of th e whorl
b en eath the su ture, a nd mer ges ther e wit h th e wa ll pro pe r o f th e initi al chamber a nd th e extern al la yer s of th e firs t wh orl (pI. 44: I).
Th e st ructure of the shell fr om the nepi onic swe lling ha s been d isc usse d elsewhere (K uLl CKI , 1974). Further specime ns of Qu enstedtocera s a nd Kos nioceras with thicken ed she ll a t
th e nepi oni c con striction sho w th e sa me st ruc tu re as t ha t p re vio us ly illustra te d (K ULl CKI , I. C.,
fig. 1; see pI. 45: I , 2, 4 her ein). The speci me n illu strated in pI. 45: 3, is a n except io n, as it
differ s from the above cited st ru c tur a l p la n in the a b no rmal growth o f a backwardl y curved
section o f pri smatic layer, co nnected with format ion of an ad d itio nal, ea rlie r sec tio n o f pri smatic la yer. Di sturbances of this typ e confirm , h oweve r, th e mod e of o rigin o f sh ell swellings
p reviously suggested b y the a u thor ( KU Ll CK I, 1974, fig. 3). Thi s spec ime n a lso sho ws a break
in secreti on o f the in itial secti on of th e post-embryonic she ll, related to retreat of t he m an t le.
The pri smatic layer formed a fte r the break a lso occ urs ben eath the previo us ly formed nacreo us
laye r.
The structure of the shell after the ncpionic swelling in Kosntoceras and Quenstedtoceras
Ventral wall. - Th e vent ral wall ge nerally co ns ists o f 3 min er al la ye rs: ex ternal pri sm a t ic,
median nacreous a nd inte rnal prism ati c. The typical d evelopment of th ese lay er s has been
de scribed by several a utho rs, including BIRKELUND ( 1967), BIRK ELUND a nd HANSEN ( 1968,
1974) a nd ERBEN et al. (1968, 1969). Th e nacreous layer o f Ko sni oceras and Qu enstedtocera s
is built of stacks of tablet s as is typi cal of mo st gastrop od nacre a nd as is in the lenticular
nacre o f many bivalves (TAYLOR et al. 1969). The stac ks are clearly to poorly marked o n c ro ss-secti on s (pI. 35: 6). The internal prism atic layer as typicall y developed di spl ays a regul ar arrangem ent of prisms. It is thickest close to th e umbilical sutu re , th inning ou t a nd so me t imes
completel y d isappearing o n the whorl side s (pI. 48: I). Th e layer ed str uc tu res of th e int ernal
prismatic la yer, obser ved under th e op tica l microscope by BLIND (1975) is a lso visibl e o n SEM
micrograph s of etched longitudinal (pI. 46: 6) a nd tran sver se (pI. 48: 2; pI. 44: 2) cross-sections.
THE STRUCTURE AND DEVELOPMENT OF AMMONITE SHELL
121
Longitudinal sections through ventral wall display discontinuities resulting from breaks in
secretion. The discontinuities vary in length and are sometimes confined to the external prismatic layer (pI. 47: 4, 6) or cut both the external prismatic and nacreous layers (pI. 47: 7).
No similar discontinuities were found in the internal prismatic layer. The beginning of a new
phase of secretion does not require retreat of the mantle margin. The course of discontinuities
in particular layers reflects the course of the secretory zone in particular sections.
Dorsal wall. - The dorsal wall from the post-embryonal stage, as seen in medial and
paramedial sections, begins at a sharp boundary between the internal prismatic layer of the
second whorl and the wall proper of the initial chamber, and the external prismatic layer of
the first whorl (pI. 44: 3; pI. 42: 3, 4; pI. 43: 1a). This sharp boundary presumably results
from a change in secretion preceding the deposition of the internal prismatic layer, i. e. the
section secreting the external component of the dorsal wall in the dorsal zone forming the
later wrinkle layer. Sections through the lateral part of the initial chamber show that the dorsal
wall consists of the nepionic swelling of the shell with all the elements well-developed (pI. 45: 5).
It follows from that illustration that the nepionic swelling, along with all the components,
passes towards the posterior into the dorsal wall of the first whorl, i. e. the external layer of
the initial chamber. It should be assumed , therefore, that equivalents of all the components
distinguished in the ventral wall of the first whorl are involved in the construction of the
dorsal wall as far as the stage of formation of the nepionic swelling ; and that the inner prismatic layer does not become the main component of the dorsal wall before the nepionic swelling (pI. 46: 4,5,6; pI. 47: 1).
The dorsal wall of the second whorl (pI. 48: 3, 5) accurately duplicates the microstructure
of the first whorl. A micrograph of a section of the dorsal wall between the second and third
whorl (pI. 48: 4) shows that the ornamented inner prismatic layer, representing the dorsal
wall of the succeeding whorl , rests on a relatively even external surface of the ventral wall of
the preceding whorl. When the two walls are broken , conellae-Iike prisms are left on the ventral
wall. The prisms are uniformly distributed as are knobs from the dorsal wall, They represent
torn-out fragments of the inner prismatic layer, and mark places where the dorsal wall (i. e. inner
prismatic layer) was more closely adjoining the ventral wall of the preceding whorl. The structure of the dorsal wall becomes much more complex from the end of second whorl in both
Quenstedtoceras and Kosmoceras.
fj)
Longitudinal sections (pI. 46: 1-6; pI. 47: 1-8) show that the external prismatic layer of
the preceding whorl is overlaind by structured quite different from the normally developed
inner prismatic layer, in the form of a layer variable in tickness (see fig. 9). Triangles linked
to one another by peeks on the sections represent the basic components of this layer; they
are overlain by normally developed inner prismatic layer. Longitudinal sections of specimens
of Quenstedtoceras at various developmental stages with body chamber preserved allow the
distinction of several main stages in the development of the dorsal wall :
Stage (I). Triangular structures with one longer side adjoining the ventral wall and other
longer side adapically oriented, appear on the ventral side of the preceding whorl close to the
aperture. The somewhat concave shorter side of the triangular structures display a short,
also adaperturally oriented projection at the base (pI. 47: 2-4, 6-7; pI. 46: 1,2; fig.9A).
Stage (2). Elongation of the long sides of these structures in an ad apical direction results
in the merging of their bases (pI. 46: 3; pI. 47: 5; fig. 9 B).
Stage (3). Infilling of depressions between peaks of the triangles (pI. 46: 3; pI. 47: 8;
fig. 9C).
Stage (4). Covering of these structures by a prismatic layer (pI. 46: 4-6; fig. 9 D). The
position in relation to the aperture, and the mode of development of the elements (I and 2)
discussed above indicates that they represent components of the so-called wrinkle-layer, whilst
the other elements (3 and 4) represent parts of the inner prismatic layer. The microstructure
of the elements appearing in stage (I) is still poorly known. It may be stated , however, that
122
CYPR IAN KU LICKI
it differ s markedly fro m th at o f th e pri smat ic and nacreous tissues. Exte nsive studies have
show n th at th e arran gem ent of min eral a nd organic compon ents is fairly homogeneous, beco ming regular only towa rds th e sho rt side of th e tr ian gle. Par all el elements are also visible
arr a nged on e above a not her, a nd so mew ha t resembl ing a single "s ta ck" of nacre. It is still
a n ope n que stion whet her thi s microstructure is origina l or a result of di ageneti c cha nges .
The microstructure of th e remain ing elements of th e d or sal wall ment ioned under (2)-(4)
a bove is pri sm ati c a nd spher ulitic-prisma tic . T he degr ee of o rde ring cha nges from laye r to
layer , wh ich resul ts in so me very sha rp bounda ries bet ween layers (pI. 46 : 4-6 ; pI. 47: 1).
1
A
B
Fig. 9
Successive stages in the for mation of the dorsa l wa ll. A -B - the outer co mponent of the dorsal wall, in the for m of
a wrinkle-layer visible in the a nter ior parts of body chambers. C-D - the inner componen t of the dorsal wall, coveri ng
the wrinkle-layer visible in the poster ior parts of body cha mbers a nd phragmocones
Th e dorsal wall is co nnected with th e lat er al wa ll of the shell at th e umbilical sut ure. A s
was previo usly state d by ERBEN et al. ( 1969), BIRKELU ND a nd H ANSEN (1968, 1974), To z ER ( 1972)
a nd others, th e two external layer s (the exte rnal pri smatic a nd nacreou s) wedge out at the
umbilical suture (pI. 44 : I ; pI. 48: I), whilst th e inn er prismat ic layer stilI co ntinues on the
dorsal side, although usuall y thinnin g out in compar ison to its development a t th e umbilical
bend (pI. 48: I).
Plat e 44: I rep resent s a tran sverse section thro ugh th e initi a l ch amber, th e end of th e first
wh orl (nepi onic swelling) a nd a hal f of th e seco nd whorl. In th e case of th e umbil ical sut ure
from the half of the seco nd whorl, it is clea rly visible th at a layer of prismatic character underlies th e inner prismatic layer , a nd penetrate s deepl y ben eath the layers wedgeing out at th e
suture. Th e former layer may be interpret ed as a n equivalent of th e wrinkle-layer ; a wrin kle-layer occurring in the same position was described a nd illu strated by TozER (1972, fig. 3).
In the case of the ending of th e first who rl illu str at ed here (pI. 44 : I) it may be noted that the
prism atic layer passin g beneath th e umb ilica l sut ure extends int o th e external pri smatic layer
of th e first wh orl on the o ne hand , a nd passes smoo th ly int o the thicken ed wa ll proper o n
th e sides of th e initial cha mber on th e othe r.
Se pta. - The min eral tissue and the relat ion to th e wall s of t he she ll of the first sept um
(proseptum) a re de scrib ed a bo ve. The mineral tissue of th e seco nd septum is differentiated ,
however , bein g ch ar acterized by a pri sm atic structure in medi al and paramedial sections
(pI. 28 : 2; pI. 30; 2) a nd a nac reo us struc t ure in lat eral sectio ns (pI. 42: 3; pI. 48: 6). In Kosmo-
Til E STR U CT U R E A ND D EV ELOPM ENT O F AMMO NI T E SHELL
123
ceras, in which the siphon penetrates th e seco nd sc pt um centrally, it is possible to trace a continuou s tran sition from the pri smatic tissue from the sur ro und ing of the connecting ring to
the nacreous layer of the remaining part of the septum (pI. 34: 2).
Nacreous tissu e is the main component of all th e remaining septa in both genera. The
exception is that in Quenstedtoceras, a spherulitic-pri smatic layer is relatively well developed
a s a second component of the sept urn on the ventral part of the ad apical surface close to the
siph on (pI. 33 : 4). In the dorsal part , spheru litic-p r isma tic tissue occurs as a ledge from the
adapical side of th e septu m covering the sut ure between the septum and the dorsal wall
(pl. 46 : 4, 6).
In the stage s following th e first two whorl s in Kosnio ceras the spherulitic and prismatic
components of the septum are better developed than in Quenstedtoceras. The ad apical surface
of the septurn is covered with by spher ulitic-p risma tic tis sue in the ventral part (pI. 35: 5-6).
Similarly developed sp her ulitic-p risma tic tissue is found on the ad a pertu ral surface of the
septum wh ich is, however, sit ua ted o n the d o rsal side in relation to th e septal neck (pI. 41: I).
Prismatic tissue, characterized by irregular development of prisms, is found on the adapertural
surface of the septu m on the ventral side in relation to the sep ta l neck.
The relation of sept um to shell walls is found to be the same as wa s described by BLI ND
(1975) on the basis of Callovian material mainly derived from Lukow, A continuous transition
from nacreous se ptu m to prismatic dorsal wall in an adapertural direction is clearly visible
(pI. 44 : 2). So-called sutura l infilling is here less o bvio us than in BLI ND 'S sa m p les. The sut ura l
infilling is sometimes lacking, as is the case in early growth stages, or is very poorly developed
(pI. 46: 5). The best developed sutural infillings were found on the fourth whorl of Kosmoceras (pI. 35: 5, 6).
DI SC USSIO N A ND I NT ERPR ETATIO N
Initial chamber . - ERBEN et al. (1969) interpreted the wall of th e initial chamber of ammonites as a structure buil t of layers which wedged out successivel y towards the exterior. The
first o f these lay er s were sa id to be subprisma tic in structu re, and th e lat er la yers fully prismatic.
BIRK ELUND (1967 ) and BJRK ELU :-JD and HA NSEN (196 8, 1974) di stinguished two main layers
in the wall of the initial chamber: int ern al pri sm atic, and external , built of irr egular crystals.
The results of the author's studies confirm the bipartite nature of the wall of th e initial chamber,
showing at th e sa me time that th e internal pri sm atic layer represents the extern al wall proper
of the initial chamber , and th at the external layer with less regularl y distributed mineral comp on ents represents th e dorsal wall o f the next (fir st) whorl. Thi s is indicated by:
(I) lon gitudin al sectio ns wh ich sh o w that sept a are ch aract eri zed by ad a pert ura lly oriented
mural parts so st ro ng ly developed that they so meti mes penetrate deeply ben eath younger
sep ta, and (2) tran sverse sectio ns of the fir st wh orl and the initi al chamber which sh o w that
a ll of th e layer o f th e first whorl participating in the formati on of th e dorsal wall occur directly
on the ext ern al wa ll proper of the initial ch amber. A cco rd ing to ERB EN et al. (1968, 1969),
BIRK ELU ND (19 67), BIRKELU ND a nd HA NSEN (1968 , 1974) the wall of the initial ch amber wedges
o ut clo se to th e fir st septum . The author's stud ies do not co nfirm this, indicating rather the
o pposite; th ey sho w th at the exte rn al pr ismatic layer of the first wh orl represent s a continuous
exten sion of the exte rnal wall p roper of the initial chamber , and only a thickness decrease
o f th e wall proper of th e initial ch amber is obse rved along the tran sition b etween the ventral
wall of the initial cha mber a nd the first wh orl (see p. 34). The a b ov e mentioned authors did
not give any illustrati o ns wh ich sho wed un equivocally the wedging out of th e wall of the
initi al chamber. E RBEN et al. (1969, pI. 3: 2) illu strated only a decrease in thickness of the wall
of th e initial chamber, and th e illu stration given by BIRK ELU ND and HANSEN (1968, pI. 2) is
n ot co nvincing. The specimens fro m the Maestrichtian of western Greenland st ud ied by BIR-
124
CYPRIAN KULlCK I
KELUND a nd H ANSEN are d iagenetica lly altered, as was also emphas ized by E RBEN et al.
( 1969 : 44).
A review a nd co mme nts o n views o n th e str ucture of the dor sal end of th e wall of the
initial chamber a nd its relati on to the pr osep tu m were given elsewhere ( KULIC KI, 1975).
Th e flange is here int erp ret ed as th e dorsal end of th e wall of th e initi al chamber, separat ed from it by a di scontinuity. This term was used in th e sa me sense in an earl ier paper of
th e pr esent a utho r (KULICKI, 1975). Th e end of th e dorsa l wall of th e initi al ch amber illustrated
th ere (l. C., figs I a nd 2) with th e pr oseptum was misint erpreted , as th ere is no flan ge here
that would match th e a bo ve definition , a nd th e d iscontinuity show n in th ese figures sepa rates
the mural part of the pr oseptum from th e externa l wa ll pro per of the in itial chamber.
Dorsal wall. - It follows fr om th e a bove observatio ns th a t the dor sal wall of the a mmo nites
st udie d is built of two main compon ent s:
( I) a n int ernal compo nent linin g th e inside of th e shell sides a nd corresp ond ing fully to the
inner pri smatic layer, a nd (2) a n exte rnal compon ent , resti ng d irectly on th e preceding whorl
a nd so metimes penetrating beneath t he umbili cal suture.
With respect to point ( I): th e inn er pr ism ati c layer passes witho ut a ny break onto the lateral
wall of th e shell. Its secretio n was related to a n epi the lium deve lo ped beneath the muscle
a tt ac hme nts of am mo nites - it correspo nds to th e myost racum or myostr acal layers of workers on bivalves a nd ga stropod s (e.g. TAYLOR et al. (1969)). Va rio us secto rs of mantle sur face,
connected with different muscle gro ups, were presum abl y res po nsible for th e multilayered
nature of th e inn er prismat ic layer of th e d or sal wa ll. Attachment fields of mu scles of Recent
Nautilus ar e situa ted in th e posteri or part of the bod y. The a ppearance of th e first elements
of the inner pri smatic layer in the interi or of th e b od y chambe r of am mo nites indicates th at
th e main att achme nts of mu scles were similar ly loca ted . BLI ND (1975) has shown that the
most inte rnal compon ent s of inn er pri smatic layer (fig. 9 D) a re con nected with subepithe lia l
mu sculature.
With respect to point (2) : The exte rna l component o f th e do rsal wall first ap pears outs ide
th e ap ica l part of th e initial chamber as a subprisma tic layer on th e wall pr op er of th e initial
chamber. The subprisma tic layer is covered with very th in, so metimes poorl y visible laminae
of prismatic mat eri al, ident ifiabl e with th e mu ral pa rt s of septa . In the early onto geny of the
dorsal wall, in whi ch a pica l and dorsal pa rt s of the initial cha mbe r are formed , th e whol e dorsal
wall is limit ed to th e laminae of the mural pa rt s of septa . No elements corresp onding to the
exte rna l co mpo nent of t he d orsal wa ll were found bet ween the mura l lamin ae a nd the wall
pr oper of the initi al cha mber. Th e exte rnal com po nent of th e dorsal wall is developed as
a pri smati c layer in th e middl e of th e seco nd who rl, a nd is alrea dy th e typi cal wrinkle layer
on th e third whorl.
The zone secret ing the external component of dorsal wall. - It is beyond a ny doubt th at
both the mantle subzo nes secreting th e externa l wa ll of th e first whor l were involved in th e
secretion of th e external com pon ent of th e dorsal wa ll pr ior to the end of fo rma tion of the
nepionic selling. This is indica ted by t he clearl y co ntinuo us tran sition between the nacreous
tissue of th e nep ionic swelling a nd th e sub prisma tic tissue of the exte rnal co mponent of th e
dorsal wall, clearl y visible in tran sver se sectio ns throu gh th e umbilical sut ure between the
initial cha mber a nd first wh orl. The tr an sition from th e external prismatic layer to the subpri smat ic tissue continuing above th e umbili cal suture a nd con nected with dorsal wall, is also
clearly di scernible. Th e externa l pri smatic layer co nnected with the d or sal wall beneath th e
umbilical sut ure on the other side pr oduces a pr ojecti on di rected to th e outs ide of the sh ell.
Such development of the external pr isma tic layer is possibl e only whe n a secretory projection
directed to the outside of th e umbili cal suture is dev elo ped at th e mantle margin on th e ventral
wall close to th e umbilical sut ure, a nd in front of th e a per ture.
In th e middl e of th e seco nd whorl the exte rnal co mpo ne nt of the do rsal wall penetrates
deepl y beneath th e um bilical sut ure, being sepa ra ted from th e nacreou s a nd extern al pri s-
TH E STR UCT UR E AND D EVELOPM ENT O F A'I1'1lONlTE SH ELL
125
matic tissues by a distinct discontinuity. Thi s indicates that the prismatic tissue of the external
component of the dorsal wall was secreted in front of the apertural margin , despite the fact
that not only a mantle margin but a br oad secretory zone could have been responsible for
its formation .
Wrinkle-layer. - Thi s layer occurs in post-Triassic a mmonites of the fam ily Graphoceratidae (Ammonitina), a few Middle Jurassic perisphinctids (SENIOR 1971: 113) a nd in Sonniniid ae and Liparoceratidae (BAYER 1974). It is also fairly common in Paleozoic and Triassic
ammonites (WALLlSER , 1970; HOUSE, 1971 ; TozER, 1972 and others).
In th e Quenstedtoceras studied the first elements of th e wrinkle-layer are found close to
the aperture, enlarging somewhat toward s the interior of the body chamber (figs. 9 A, B).
The wrinkle-layer was never found outside the umbilical sut ure in trans verse sections of the
specimen s studied . According to WALLlSER (1970), SENIOR (1971) and HOUSE (1971), similarly
developed structures on shell flank s belong to the same category and are also described as
"wrinkle-layers ". According to TOZER (1972), howev er, th ey a re of a different origin, a nd
he suggests that layers from shell sides a nd venter should be termed " R itzstreifen" . BAYER
(1974) has identified th e wrinkle-layer o f a mmonites with a corrugated inner pri smatic layer.
The gradual developm ent of individual wrinkles in Quenstedtoceras ind icate s that the y
were secreted in a relat ively wide zone. Th e viewpoint of TOZER (J 972: 651) is ju st the opposite ;
on the ba sis of dat a present ed by STENZEL (in: MooR E, 1964 : K 72), TOZER assumes that the
black film of Nautilus is presumabl y not secreted by the mantle sur face, but rather its margin.
This mod e of secretio n is also suggested by TozER for the wrinkle-layer of a mmonites, which
he suggests is comparabl e with th e black film of Nautilus in both distribution and ornamentation (SENIOR , 1971 ; To z ER , 1972). In Nautilus this organic layer is covered by nacreous
material secreted by a relat ively wide zo ne. N acre ous tissue do es not occur on the dorsal wall
of ammonites, so it may be sta ted th at the wrinkle-layer of a mmonites is th e same as the
black film of Recent Na utilus in development. The former , however , is secreted by a larger
part of mantle surface, as is the nacreou s layer of th e dorsal wall of Nautilus. Onl y primary
elements may be secreted by the mantle margin (fig. 9 A).
S epta. - The proseptum originate s in a fu rrow surrou nd ing the po steri or part of the
body, which gradually increas es in depth during secretion (comp. KULICKI 1975). There a re
some premises th at the furr ow did not origina te sim ulta neo usly along its whole length , but
first in ventral region , close to th e cent er , a nd subsequently in other parts of th e bod y. Paramedi al sections of the ventra l ar ea sho w a swelling of the medial layer which is involved in
the formati on of th e ba sal part of the pr oseptum. This indicates that th e fur row o riginates
here earlier than the medi al layer (fig. lOA). In longitudinal sections passing through the
lateral parts of th e initial chamber , the medial layer is reduced in thickness, a nd is not involved
in th e formation of the basal parts of the proseptum. M oreover, the eldest elements of th e
prisms are not di sturbed here. A disturbed pack et of pri sms is situa ted at th e middl e of thi ck
inner layer and acts as a suppo rt for the pr oseptum (fig. IOB). This indicat es a retard ation in
formation of furrow a nd pr oseptum in relation to both the medi al layer a nd th e first ph ase
of secre tion of the inn er layer. There is no reason to assume a synchroneous o rigin for the
remaining septa throughout the surface. In the case of the seco nd septum, the pri smatic and
nacreous tissues are secreted at the sa me time. Most probably th e zone of secretion of the
second septum was mosaic in cha rac ter.
The mode of formation of the initial chamber and first whorl, and the development of secretory
zones
The wall proper of the initial ch amber was the first element to be secreted . It was formed
initially by a cap-like secreto ry zone, which widens gradually in time. The a pica l part of the
zone gradually lo st its ability to secreti on , a nd become tubula r (fig. 7 A). This secreto ry zo ne
126
C Y I' R IA N K ULI C K I
was uniform a nd ph ysiol ogicall y un differ entiat ed , as is ind ica ted by th e uniformity of secreto ry
product s.
The flan ge from th e d orsa l part o f th e initial chamber d oes no t ex te nd across th e whole
wid th o f th e initi al c ha mb er, a nd it is se pa ra ted from t he wa ll pr o per by a d iscontinuity, indi cat in g th at it was fo rm ed du ring sec reto ry ph ase wh ich foll owed t hat resp on sible for the
formati on of th e d o rsal part of t he wa ll proper. Th e end of the fla nge, or lateral par ts of the
do rsa l wall of th e init ial cha mb er, reflect a b reak in secret io n, as th e next mate rial d eposit ed
in this part of th e init ial cham ber wa s th e do rsa l part of the p ro septum (fig . 7 C).
T he medi al laye r occurs throu ghout a large pa rt of th e interior of th e ve nt ral region
ben eath the wall pr o pe r o f th e in it ial chambe r, wedgi ng ou t in whe re t h is wa ll is co n nected
with the first who rl. T he wall proper o f the ini tial cha mb er d oes no t wedge o ut t o the outside
A
B
r-----"----
-
------, c
F ig. 10
Schemat ic sec tio ns th ro ugh the ventra l wa ll of th e
ini tia l c ha m ber and proscpt um . A - med ian sectio n .
B - la teral sectio n, C - extreme la ter al section
as was sugg ested by E RBEN et al. ( 1968, 1969), BIRKELUN D ( 1967), BIRK ELU ND and H ANSEN
(196 8, 1964) and K ULl CKI (19 75), bu t co nti n ues, wi tho ut a ny brea ks , in the fo r m of the extern al layer of th e firs t wh orl. It t hus a ppears that th e me di an layer wa s fo rmed by a very
wid e secreto ry zo ne sit ua ted direct ely behind the zo ne secreti ng th e wa ll p ro pe r of the initial
cha m ber. At th is stage, th e originally uniform secretory zo ne beca m e di fferentiat ed into two
subzones (fig. 7 B). In th e d orsal part, th e secretio n of th e med ial la yer may correspond to the
sec ret io n o f th e flan ge but there is n o ev ide nce for the ir sy nc hron ism. The appearance of
a swe lli ng o f th e medi al la yer a t th e site o f futur e format io n o f th e b ase of the p roseptum in
th e medi al and pa ram edi al sec tio ns indicat es a n ea rly phase of formati on for the circular
fur row.
Th e next stage inv o lved the secretio n of the prose pt um togeth er wit h th e inner p rismat ic
la yer o f th e init ial cha mbe r, th e ve ntra l part o f th e first whorl a nd th e elo ng ate mural part
o f th e proseptum in th e d orsal regio n. At thi s sta ge t he secre to ry zo ne was tubular a nd cle arl y
differ entiated in ventral , la teral , a nd part o f dorsal regio n in to two subzones : a narrower one,
sec ret ing t he ex te rna l prism ati c layer o f the first who rl a nd a w ide r o ne, sit ua ted b ehind the
former , a nd sec re t ing th e inn er pr isma tic la yer o f th e ini tia l ch ambe r, prose pt um a nd medi al
la yer of th e first wh o rl (Iig , 7 C) . Thi s stage was cha racter ized by th e p rogress ive d evelopment
o f the furr ow, in wh ich th e prosept u m o rigi na ted (com pa re K U Ll C KI 1975).
Fo llow ing th e form a tion o f th e flan ge, but befo re the format ion of the d o rsal part of the
p roseptu m, th e dorsa l part of th e b od y was bent strongly. T his is reflected by th e way in wh ich
th c d o rsal p art o f tube of th e firs t wh orl formed a t the co ntact w ith th e wall of the initi al chamber.
A change in di recti on o f growth resulted fro m continuou s, rather than interrupted secretion
in th e ve nt ra l pa rt a nd th e terminati on o f sec re tion in t he dorsal p art.
Th e fo rmat io n o f th e prosep tum was accom pan ied by a w ithd rawal of th e so ft ti ssues from
th e initia l ch amber. Associat ed wi t h a slowing of th e form a ti on of the late ral parts of the
pro scpturn , the p rocess o f ret reat o f soft tiss ues from th e in it ial cham be r was adva nced so that
th e prosep tum extende d o nly in to th e me d ia l pr ismatic layer of the firs t wh orl in these regions
(fig. 9 C; see a lso B IR KELU ND a nd HAN SEN , 1974, fig. 2) . When the proseptum wa s completed
THE STRUCTURE AND DEVELOPMENT OF AMMONITE SHELL
127
a significant po rtion of wall of the first whorl was also finished. The wall was secreted in the
ventral and lat eral regions of the first whorl by a secretory zone that was subd ivided int o two
subzo nes, and corresponded to the zone secreting dor sal wall of the first whorl. In the proximity of the flange. the dor sal wall was initially limited to the mural parts of the proseptum
and the first sepia, ,I nd had an essentia lly prismat ic structure. Th is ind icat es that the secretory
zone was not differentiated into subzones in the dorsal region. The differenti ation is reflected
in the appearance of an exter nal component of the dorsal wall in the for m of subprismatic
tissue in the dorsal wall, outside the a pical part of the initial cham ber. This differentiation
indicates that the zone of secretion of the mural par ts of septa sepa rated fro m the zone secreting the externa l compone nt of dorsal wall. The external compo nent of dorsal wall shows no
differentiated microstr ucture, which indicates tha t the secretory zone was also undifferentiated.
This undifferent iated zone was connec ted, witho ut any brea k, to the zone which secreted the
ventral a nd latera l walls of the first whor l; this, however. was differentiated into two subzo nes.
In the ventra l region, the zone of secretion of the mural parts of th e septa were clearly differentiated into subzones , as is indicated by the a ppearance of a discon tinuity between the inner
prismatic and medial subpr ismatic layer of the first whorl. In the case of septa built of nacreous
tissue, the secretory zone of the free septa l wall was di rectly connected with the mur al secretory
zo ne.
Suitably different iated secretory zo nes were proba bly associated with the form ati on of the
a ngular deposits of septal necks, and the prismat ic a nd spherulitic-pris matic components of
septa. One cannot dismiss, however, the possibility that these depos its are the products of
some inorganic (diagenetic) depositio n: an inorganic grow th of some calcium ca rbonate elements was demonstra ted by BANDEL and HEMLEnEN (1 975).
The mode of format ion of the nepionic swelling of the ammon ite shell is described elsewhere (K ULICKI, 1974).
Thi s comp ari son of the secretion zones and their products formed before and after the
nepionic swelling demonstrates that:
- Before the for matio n of the nepio nic swelling the zone secreting the wall was subdivided
into two subzo nes: (a) a subzo ne secreting the externa l prismatic layer of the first whor l,
and (b) a subzone secreting the med ial subpri smatic or prismat ic layer of the first whorl situated
behind the nepionic constrictio n.
- After the nepionic swelling (e.g . in the postembryo nic shell) the zone secreting the shell
wall was also subdivided into two subzones : (a) a subzone secreting the externa l prismatic
layer and (b) a subzo ne secreting the nacreous layer.
ERBEN et al. (1969: 26) a nd KULlCKI ( 1974) noted that the external prismatic layer preceding the end of the nepionic swelling, th at occurring at the backward s curving section, and
the externa l prismatic layer of the postembryon ic shell were str uctura lly identical. It is the refore
highly probable that they were for med by the same secretory zone.
THE QUESTION OF EARLY DEV ELOPM ENT IN AMMONITES
Two main points of view on the embryogenesis of a mmonites can be distinguished :
(I) The assumption that there a re th ree stages : (a) embryonic, limited to the initial chamber,
(b) lar val, of the troc ho phore or veliger type, and equiva lent to that pa rt of the shell as far
as to the nepionic swelling, and (c) postlarva l, cor respondi ng to the remainder of the shell
(ERBEN 1962, 1964, 1966; ERBEN et al., 1968, 1969 ; LEHMANN 1976; SHULGA-NESTERENKO 1926;
ARKEL 1957; MAKOWSKI 1971 ),
(2) The assump tio n that develo pment was simple, compris ing only two stages : embryo nic,
comprising t he shell as far as the nepio nic swelling, a nd pos t-embryonic compris ing the
remainder of th e shell (SII IMANSKY 1954 ; RUZHENCEV and SHIMANSKY 1954 ; D RUZCZIC 1956;
128
CYPRIAN KULICKI
DRUZCZIC and KHIAMI, 1970; RUZHENCEV 1962; BOGOSLOVSKY 1969; BIRKELUND and HANSEN
1974; KULICKI 1974).
RUZHENCEV and SHIMANSKY (1954: 41) applied the term "larva" in relation to ammonites
neither to a veliger nor a trochophore but rather simply to an underdeveloped young individual , as do teuthologists in relation to underdeveloped individuals just after hatching. This
concept was subsequently used in the same way by RUZHENCEV 1962; SHIMANSKY 1954; and
BOGOSLOVSKY 1969. In his earlier paper and here , the present author (KULICKI 1974) termed
this stage "pseudolarval".
The supporters of the first viewpoint assume that the constriction at the front of the initial
chamber was the boundary between embryonic and larval stages. According to ERBEN et al.
(1968, 1969), BIRKELUND (1967) and BIRKELUND and HANSEN (1968, 1974) the subprismatic
tissues of the first whorl disappear and the prismatic tissue of the first whorl appears in the
proximity of the whorl constriction. A shallow ventral sinus there also appears in growth
lines (ERBEN 1962, 1966). The data previously published (KULICKI, 1974) and recently assembled
show that there are no changes in microornamentation between the two parts of the shell in
Mesozoic ammonites. There is also no discontinuity, represented by either a line on the shell
surface or a secretory break in cross-section. The wall proper of the initial chamber always
passes , without any break, into the external prismatic layer of the first whorl. The appearance of a shallow sinus in the growth lines, noted by ERBEN (I. c.) and interpreted as indicating the position of a locomotive organ such as a velum may also be interpreted as related
to the development of the funnel in the embryonic stage , as was emphasized by BOGOSLOVSKY
(1969: 66). In Recent mesogastropods, in which larvae with a protoconch hatch from the egg
envelope, the point of hatching is marked by a change in surface ornament or the appearance
of growth lines (ROBERTSON 1972).
Comparison with Recent Nautilus is hindered by our lack of direct observations of this
animal. The concepts explaining maximum size of embryonal shell of Nautilus assume that
hatching is marked by a discontinuity (WILLEY 1896; BLIND 1976) or a change in ornamentation (EICHLER and RISTEDT 1966). The point of hatching is not marked in this way in ammonites; changes concern shape only. The hypothesis that "I Wachstumsanderung" of ERBEN
is connected with hatching from the egg envelope cannot be maintained .
Supporters of a simple development of ammonites assume that the nepionic swelling represents the boundary between embryonal and postembryonal stages. According to ERBEN et al.
(1968) the nepionic swelling reflects metamorphosis which resulted in the changes in the
posterior part of the body, which are indicated by changes in the suture line between prosuture
and second suture. Thus so far there were no data which indicated that the nepionic swelling
originated simultaneously with the change in shape of the posterior part of the body between
the first and second sept a. The data showing the concentration of septa and length of body
chamber make it possible to assume that there were already some septa when the formation
of nepionic swelling terminated (KULICKI 1974). A change in shape of the posterior part of
the body between the first and second septum may result from difference in formation of the
two elements. When the first septum remains in the furrow surrounding the posterior part of
the body the second septum represents the product of the posterior part of the body.
A difference in structure of the first whorl before and after the nepionic swelling reflects
only the secretion products of the posterior subzone which was secreting the subprismatic
and/or prismatic tissues of the medial layer of the first whorl before the nepionic swelling,
and the nacreous tissue following nepionic swelling. The swelling formed during a phase when
the margin of the mantle halted or even retreated , together with a change in the secretions
of the posterior subzone of the mantle margin (comp. KULICKI 1974). Differentiation in secretion of the mantle margin into two subzones is visible before and after formation of the nepionic
swelling. The differences in secretory products of the posterior subzone may result, and be
correlable with , processes acting just before hatching.
THE STRUCTURE AND DEVELOPMENT OF AMMONITE SHELL
129
The adaptive significa nce of th e nepionic constriction may ha ve been as foll o ws:
(1) it ser ved to streng hten a wide zo ne a t th e mar gin of th e first who rl during hatching from
the egg envelopes;
(2) it a cted as ball ast to the a pert ura l margin during th e first ph a se of development after
hatching, help ed th e a nima l t o maintain th e a pp ro priate flot ation positi on ( KULlCK I, 1974 :
213 ).
The functi on of th e nepi onic swelling as a su ppo rti ng for th e a pe rtural margin during
hatching may be expl ain ed by the stead ily incr ea sing mechanical pressure of the em bry o on
both the egg enve lo pe a nd the a pertura l m ar gin closely adjoining the en velope (co mp. KuL1CKI, 1974). The weighing of the a pertural mar gin in th e first post-hatch ing ph ase may be
explained by the fact t ha t a significant part of th e first wh o rl preced ing the nepi onic swelling
(more th an a half who rl) di spl ays reduced growth indices (gr ow th of whorl height, width and
spira l radiu s ; KULlCKI , 1974). Thi s produces a sha pe close to sphe rica l, with th e initial chamber
close to the centre. In thi s sit ua tion the centre of g ravi ty o f th e shell and th e centre of buoyancy
of the initial chamber a re situa ted close together (soft tissues may be negl ected in this analysis
as thei r density wa s close to th at of sea wat er , whi ch results in th e loss of static eq uilibrium).
The formation of th e nepi oni c swelling results in th e shift ing of th e centre of gravity towards
th e a perture, a nd com pen sat es th e lack of gr owth in width , heigh t a nd spira l ra d ius.
DRUZCZIC a nd KHIAMI (1970) int erpreted th e nepi oni c swe lling as a st r uct ure formed in
a result of a growth pause in th e first post- hatch ing stage. I n t urn, followin g KULl CKI (1974: 213)
the fact th at the egg enve lo pes a re attache d to th e she ll during th e growth of th e first whorl
may explai n:
(1) The ornament at ion such as ribs a nd sp ines th at is typic al of postembryoni c fo rm s, but
is lacking in embryon ic shells.
(2) The ep hemera l (tra nsitory) occur re nce of growth lines o n th e embryonic shell. This phen omenon may be partly exp lained by a more sta ble ph ysico-ch emical co nd ition and food
supply within the egg enve lope.
(3) The presence of lon g fina l sec tio n of th e embryo nic shell, witho ut a ny increase of par ameters of the spire, which results in a subspher ica l she ll shape.
The gela tinous egg enve lo pes of recent Decapoda gr ow during embryogeny (Z UEV a nd
N ESIS 1971), as in th e ca se in so me marine gas tropo ds (ROGINSKAYA 1962 ; SIfUTO 1974).
The egg envelopes of a mmo nites, de scribed by LEHMANN (1966) a nd M ULL ER (1969) are
simila r in size to th e in itial ch amber. Becau se of their small size they ma y be interpreted a s
egg envelopes in the ea rliest ph ase of development .
The present author investigat ed a series of minute ammonites with full y developed nepi onic
swellings and more than o ne sept um from Oxfo rdian limeston es of th e Jagua Fo rma tion in
west ern Cuba. The mass occ urre nce of th e am mo nites (2 to 4 at th e a vera ge in thin section 3
to 4 ern" in surfa ce), th e lack of ea rlier stages a nd sca rcity of so mewha t o lder forms suggest
rapid and simultaneous death of th ese animal s, connect ed , perhaps, with so me critical event
such as hatching.
BOGOSLOVSKY (1969 : 4) d iscu ssed the m ain directi on of evo lutionary ch an ges of th e embryonic she lls of ammoni tes ran ging from primiti ve Lower Devonian to M esozoic forms. From
the old est forms onward s th ere is a steady reducti on in size of th e initial ch amber a nd tubular
section of whorl , a nd th e degree of co iling. The maximum degr ee of coil ing is reach ed in the
Middle Devonian . C lose coiling of embryonic shell is irrever sible in a mm onites. The uncoil ing seen in heter omorphs, do es not affect th e embryonic she ll. The a bs olute size of the
embryonic shell may inc rease or decrease with time. F or exa mple, embryonic shells equal in
size or even smaller th an th ose seen in Cretaceous form s, a ppear as early as th e Lat e Devonian
and Permian (Or. V. 1. BOGOSLOVSKY, pers. in f., and a ut ho r's obser vati on s).
It is obvious that am mo nites with large em bryonic she lls mu st ha ve hatched from eggs
richer in yolk and with a lar ger initi al di ameter th an th ose of amm onites with sma ll embryo nic
9-
Pa laeo ntotog ta P olo n ica No. 39
130
CYPRIAN KULICKI
shells. As far as the size of ammonite eggs is concerned it may be stated that there was a marked
trend towards decrease in size, and that the main changes took place between the Lower and
Upper Devonian.
The small size of ~m mo n ite eggs could have been of some adaptive value:
(I) Eggs could have been produced in larger quantities, as in the case of some recent Prosobranchia, in which maximalization of survivors is achieved by large numbers of eggs rather
than their protection (SHUTO 1974).
(2) The specific character of growth of the ammonite body inside the shell does not allow
for extensive development of reproductory organs without distinct increase in body chamber
volume (in females of recent squids the reproductory organs may equal up to 35 % of weight
of body - see ZUEV and N ESIS, 1971).
Some light is cast on the size of reproductory organs by the analysis of shortening of the
body chamber of fully mature and fully grown ammonites (comp. KULICKI 1974) and finds
of egg masses inside the body chamber (LEHMANN 1966; MULLER 1969). The size is considerable, and a reduction in the size of eggs results therefore in an increase in their number without
the necessity of increase the size of the reproductory organs.
In accordance with data for squids (AKIMUSKI N 1963 ; ZUEV 1971; ZUEV and N ESIS 1971)
and prosobranchs (SHUTO 1974) hatching of individuals from small egs takes place sooner
than from large, as the time from fertilization to hatching is shorter in the case of small eggs.
Moreover, the pseudolarval stage lasts longer in the case of squids hatching from smaller
eggs (ZUEV and NESIS, 1971).
The occurrence of a pseudolarval stage in ammonites was demonstrated by KULlCKI (1974)
on the basis of shell geometry and an analysis of the relative density of septa.
The spherical initial chamber of ammonites, bactritids and nautiloids with caecum may
be interpreted as an especially well developed hydrostatic organ , well-adapted to the planktonic life of the pseudolarval stage of these form s. A simila r interpretation of the role of the
initial chamber was given by ZAKHAROV (1972) and KULICK I (1974).
MUTVEI and REYM ENT (1973), on the basis of anatomical-functional comparisons of Recent
Nautilus with a relatively short and wide body chamber and ammonites with their typically
narrow tubular body chamber, questioned the view that ammonites were capable of efficient
swimming by "jet-propulsion" and even questioned whether or not they had a funnel. The
body chamber of ammonites from the stage of formation of the nepionic swelling onwards
is poorly adapted for the use of a funnel as a locomotive organ according to these authors.
1n that situation, the role of a spherica l initial chamber a s an efficient only well-developed
hydrostatic organ, by which the ammonite, during very early growth stages, could move
vertically, is clear.
THE FUNCTIONAL IMPORTAN CE OF FOLDED SEPTA
Previous concepts concerning the functional importance of folded "a m mo nite septa may be
divided into two groups:
(I) Those inferring a physiological significance for folded septa (NEWELL 1949; MUTVEI 1967),
and
(2) Those suggesting a mechanical significa nce for folded septa (PFAFF 1911; SPATH 1919;
REYMENT 1958; RUZHENCEV 1962; TEICHERT 1967; WESTERMANN 1956, 1958, 1971, 1975a, b;
SEILACHER 1975; BLIND 1975; MUTVEI 1975) .
Recent studies carried out with models by SEILACHER (1975) and WESTERMANN (1975 a, b)
clearly demonstrate a significant physico-mechanical control on the formation of complex
septal shapes, as well as the mechanical contribution of the shape of septa to the function
of the shell as a hydrostatic organ.
THE STR UCTURE AND DEVELOPMENT OF AMMONITE SHELL
131
The physiological concept of N EWELL (1949) , emphasizing the significance of folding of
septa for increased efficiency in some physiological function as , for example, respiration, is
not supported by subsequent studies. M UTVEl'S (1967) concept that the folding of septa increased the wettable conchiolin surface in the chambers for faster liquid transport to the
siphuncle is also not convincing as , was stated by WESTERMANN (1971 : 19-20): "the corrugations
(lobe and sadd le axes) run more or less perpendicularly to the assumed directions of fluid
transport. .. Therefore the path of transport would not be widened by the corrugations but
much extended and corrugated septa would be less efficient". Experiments involving the
filling of empty Quen st edto ceras shells with water, carried out by the author, show that:
(I) When the chambers are gradually infilled with water, the water flows uniformly a nd accumulates in the depressed elements on the margins of septa between sept um and shell wall.
Depressed elements are represented by sadd les for the adapical surface and lobes for the
adapertural. The first elements infilled are thes e of the highe st order, that is the smallest, and
larger elements, of lower 01 del', are infilled later. Water infilling lob es or saddles displays
surface ten sion effects with a concave meni scus. When th e a mo unt of water in a chamber is
sufficiently small, th ere de velop a series of isolat ed reservoirs, isolated from one another by
convex elements of septa. At the stage when the siphon is in the ventral po sition , some water
is concentrated in th e space bet ween it and ventral wall and in space formerly occupied by
siphonal membranes. The shortest way through which thes e isolated reservoirs may communicate is the central surface of septum . When the water is removed from one of the elements,
as e.g. from the external lobe, it returns subsequently.
(2) lnfilling of subsequent chambers with larger diameters (1'5 -2 cm high) leads to their
complete flooding a nd, therefore, to formation of connections between particular "reservoirs",
and a weakening of surface tension so part of the water may overflow, with consequent changes
in th e orientation of th e shell. The overflowing water represents only a part of that infilling
a chamber, depending on the degree of infilling, size of chamber and degree of folding of the
marginal part s of th e septu m.
(3) When a small amount of water is introduced into the initial chamber, three water reservoirs develop: two symm etr ical, situated on the two sides of the chamber , and a third in the
middle saddle, around caecum and prosiphon.
Interpretation of functional significance of septal corrugation
According to D ENTON and GILPI N-BROWN (1966) , MUTVEI (1967) a nd the present author,
the organic conchiolin membranes covering the surface of septa probably participated in
liquid transport. A drop of water placed on the adapical surface of the septum of Recent
Nautilu s rapidly spreads and covers a large part of the ad apica l film. The experiments with
Quen stedtoceras have shown that the pre served conchioIin films are characterized by the same
property, which may be attributed to their granular surface texture (pI. 39: 4). It cannot be
excluded , however, that the nature of this surface may be of diagenetic origin since a dried
organic film from th e ad apicaI surface of Nautilus has similar but scarcer and finer granules
(pI. 39 : 5).
In Spirula, as in Nautilus, a marked decrease in concentration of salt takes place before
the appearance of first gas bubble in the newly formed chamber, which is completely infilIed
with liquid (D ENTON and GILPIN-BROWN 1966; D ENTON 1973). In Nautilus, after the pumping
out of liquid below the siphonal tube level, the contact of the liquid with the conchiolin surface
of the siphonal tube takes place via conductive organic membranes and the porous external
spherulitic-prismatic siphon layer, which also acts as a reservoir for a small amount of liquid
(D ENTON a nd GILPIN-BROWN 1966; D ENTON 1973). According to DENTON (1973) "decoupling"
of the bulk of the liquid is impo rta nt as a change in osm ot ic concentration in the zone sur-
132
CYPRIAN KULlCKI
rounding the siphon is sufficient for the pumping out of the chamber or the pumping in of
a certain amount of liquid (in Nautilus this is the liquid occurring in the pores of the external
spherulitic-prismatic siphon layer). It follows that very little osmotic work will have to be done
to prevent liquid moving either into or out of the chambers (DENTON 1973: 289).
"Decoupling" of the bulk of liquid from the siphonal surface does not take place in Sepia.
This is because the very narrow chambers are also separated by dissepiments, as a result of
which increase or decrease in concentration of salt in the proximity of the siphonal surface
is transmitted to the most distant parts of the chambers after only a few days (DENTON 1973: 290).
When the chambers of an ammonite are appropriately infilled the ratio of the bulk of
liquid concentrated in isolated reservoirs from the periphery of septum to the liquid surrounding siphon and concentrated in elements of the external lobe is comparable with the "decoupling" effect in Nautilus and Sepia. In order to pump liquid in, or out of a chamber it is
sufficient to merely change the concentration of salt in the liquid directly in contact with the
siphonal tube.
As am monites are characterized by lower indices of shell growth and a relatively longer
body chamber than Nautilus, the centre of gravity must have been situated closer to the centre
of buoyancy (in adult Nautilus macromphalus the distance between the two centres equals
6 mm according to DENTON and GILPIN-BROWN 1966). Regular distribution of liquid in
chambers and limited possibilities of overflow thus increase the stability of ammonites.
The data presented by HEPTONSTALL (1970), REYMENT (1973), MUTVEI and REYMENT (1973)
indicate that ammonites required much more liquid in the chambers of the phragmocone
than the Recent Nauti/us in order to maintain neutral buoyancy. Therefore the folding of
septal margins, which resulted in the retention of liquid in place by the action of surface tension
forces, and prevented the overflow of liquid under turbulent environmental conditions and
improved the liquid exchange in chambers enabling vertical movements in the water. They
should be therefore treated as adaptive features. The folding also increased strength of shell
against implosion. It should be stressed that the above mentioned functions are positively
correlated; the stronger the folding of septal margin the stronger is the shell and the more
numerous are the "reservoirs" holding liquid.
When phragmocone chambers are relatively large (over a dozen cm in diameter), the
elements classified in the nomenclature of the suture line as of the lower order are most important for strengthening of shell , whilst the liquid is mainly kept in the elements of the highest
order.
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133
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lI1'u1'. , 01;,. r eO.TJ oO 6 , 148.
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TOB (Zurcherctla, Salfeldicllav. - ];10.1.1. M OCl' . 0611{. Il cnum , Ilpup . ; OTn. r corr. , 2, 157- 158.
TH E STR UCT UR E AN D D EV ELOPM EN T OF A M M ON IT E SI-IEL L
135
J)orOC.'lOBCI'A M. <I) . /I .LLOr Y;I(AEUA JI. A . 19 76 . 3BOJllOl\IIi1 ccura.n.ru.rx TpyoOI( y a.\DlOlloIIJ\cii. - Fla .ieoum , ;f: .,
1, 41- 56 .
.u or Ylli AEBA JI. A . n n O.\lIIlIA;\3E T. A . 19 76 . CTPOC Il/lC IlPOTllJ(OIlXa II rppar xto rco na y TpCX HC.'I!IOIlCIICHIIX POl\ OIl
a.\ I.\IOllIlTOB ( Pseudocadoceras, Cadoceras, Kosmoceras) , - COOOII/ . AKao . Hay k TCC? , 8 1, 2 , 497- 500 .
I' OrIlIlCI{MI H . C. 19 62 . Tortoa cafie p ru.re .\I0J1JlIOCI{J( Bcn or o M op rr pa iioua Ecrrosto pcrco ii Bnonoruuccrcof C Ta IlI\IIII
MrY . - Tp. E e.lO.lfOpCKOII 1; 110.1. cmauuuu AITY , 1, 88- 108 , l·b .f\a TCJlbCTBO M OCI(OBCIWr o Yn uuepc nrer a .
P n l{EIIl\EB B. E . 19 62 . Ha riorpan Amm o no idea A.\I.\I0HO/l.f\eIl, B : O ClIOBhI na.reour onornn , M OJIJlIOCHII r onouon ornc .
I , Ofim arr '-IaCTb, 24 3- 334 , H 3l\aTc.'lhCTBO AH CCCI' , M OCHBa.
- II lIl IlMAIICHIIll B. H . 1954 . H /I;HIICn cp.\ICI{J(e CBCpllyTbIC /I coru yrr.rc na YTIIJIOll:\ClI l O ;lm or o Yp ana . - Tp .
Ila.ieoum. H ucm . , 50, 3- 146 .
IIlllMAlICH/lii , B. H . 19 54 . IrPH.\I0C lIa YTII.'lOJI.f\cn II 1;a!n p IlToIlJ\CII caroiap crcor o 1I ap TIIlIcHllI'O n pycon IO mll or o
Ypana, - Ihidem , 44. 1- 15t.
IIIYJlhrA-HEt:TEPElll<O M . H . 19 26 . Bn yrpcn ucc CTpoe HIIC parconnn a pTIll ICW[X aM.\I0IlIlTOll . - [; /0 : 1. A foCKOIICKOlO 0 011/.
I lcn. IIp/lp . , 4 , 1-2 , 8 1-98 .
3 AXAPOll 10 . .u . 19 72 . (1)Op.\HlPllIla llIlC q CHY.\\U II npocnrp ou a y aMMon o llJ.\cii. - l l a.ieomn , )1\. , 2, 64- 70 .
19 74 . H OBble J.\aml ble 0 BllyTpClIlIC.\1 CTpOCIIllll pa HOBIIlIbI xas tcu uo- yr o.u.m.rx, TpIIaCOBbIX II .\ICJIOBbIX a,\I.\ IOIIOIlJ.\cii. - Ibidem , 1, 30-41.
3 YEll
B. 19 7 1. Fonouou oruc ,\I0JIJlIOCHI! cc ncpo - Banan nu ii vracr n l-l un n iicrcor o orcea ua . 3-2 19 , !-b J\aTCJlbCTBO
,,]-[ay !{(m a .u yMKa" , K uc n .
- H ECIIC, K . H . 19 7 1. KaJlb.\Iapb I. 3- 349 , I b i\aTCJlbCTUO .,IIm lIcBaH I'Ip oxu.mr .nen uocr i," , M ocxua.
r.
EX PLANATI ON O F TH E PLAT ES
Abbreviat ions used :
an te rio r a ux iliar y dep osits
posterior a ux ilia ry dep osits
a ng ula r deposit s
bod y chambe r
ca cc u m
di sco n tinuit y
di sta l pa rt of th e se pta l neck
d orsa l wa ll
dw 1 - dorsa l wa ll of th e first who rl
dw 2 - d orsa l wall of th e second wh orl
f
- fla ngc
ieh - ini tia l ch amber
il
- inner layer of the in itia l c ha m ber
aa
ap
ad
bc h
c
d
d sn
dw
-
ip r
ml
rnp
cxc
ex p I ps
si
sm
WCI'
-
w pich 2s
3s
-
inn e r prismat ic la ye r
m iddl e la yer o f th e in itia l c ha mbe r
mural part o f the pr osepturn
ex te rna l co m po nen t o f th e d orsal wa ll
ex te rna l p rism atic layer o f the first wh orl
pr o sc p t um
s u t u ra l infillings
sip ho na l mem bra ne
wa ll o f t he co n nectin g ri ng
wa ll pr oper o f the in it ial c hamber
seco nd se p tu m
th ird se pt u rn
PLAT E 24
Nathorstites gibbosus
I. D o rsa l part o f the se p ta l nec k of t he 19th se p t u m ; x 2500 .
2. D o rsa l part of the se pt a l nec k of the 46th se p t u m ; x 600.
3. D o rsal part o f the se pta l ncck of the 43rd se p t um ; x 600 .
STOLLI'Y
136
4.
5.
6.
7.
8.
C Y P R lA N K U LI C K l
Sec tion th ro ugh
Secti on t hrou gh
Sec tio n t h ro ug h
Sectio n th rou gh
Sec ti on th rough
65th scpt urn ; x
th e d o rsal pa rt of the se p ta l ne ck a t a t ra nsit o ry s ta ge ; t he 54 th se p t u rn ; x 400.
the caec u m a nd first two sc pra : x 1000 .
th e di st al part o f th e se p ta l nec k o f t he 49t h se p t u m : x 600 .
th e se p ta l neck o f the 3Xt h sc p t u rn : >< 1000 .
th e d istal pa rt of t he au xiliary depo si ts, w ith th e wall s of the connect in g ring partl y visi b le ; the
750.
T riassic, Carn ian, Odgcoya (E . Svalb ard ), Z PA L A m . IlI / 3
P LAT E 25
Na thorstitcs gibbosns
S TOLLLY
I. Sectio n th rough the d orsa l part of the se pta l nec k of th e 94t h sc pt u m ; x 300.
2. Sec tion th ro ugh t he dorsa l pa rt of t he se p ta l neck o f th e 6 1s1 sc p t u rn ; x 1000.
a - Pr och oa n itic pa rt o f the se p ta l neck
b - Re t roch o a ni tic part o f t he se p ta l nec k
Tria ssic, Ca rnia n, Od geoya (E . Sva lba rd) , Z PAL Am 111 /3
PLAT E 26
I. Quenstedtoceras s p . j uv ., ZPAL A m 11/ 244,
a - ca ec um and pr osiph on, x 450,
b - sec tio n th rou gh a b ro ke n part o f the p ro sip hon , :< 6000.
2. Quenstedtoceras henrici R. D OUVILLE, ZPAL Am 11/ 251 , caecum and prosiphon , x 450 .
3. Quenstedtoccras s p . j uv., ZPAL Am 11/24 3,
a - caec um an d p ro si p ho n , x 450 ,
b - pr o si ph on ; '/ 1000 .
4. Quenstcdt oceras sp. j uv ., Z PA L Am 11 / 3 12,
caecu m w ith prosiph on bro ke n off; x 300 .
Lukow, Poland, Jurassic, Ca llo via n
PLAT E 27
I. Quenstcdtoccras sp. j uv. , Z PA L Am 11 / 10 2,
caec u m a nd prosiph o n : .: .1 (,0 .
.., Qnenst edt occrus hcnrici R. D o u vu. t.r., ZPA L Am 11 /252,
ca ec um a nd p rosip hou : '< 450 .
.I. Quenstcdtoccras henrici R . D OUVILl .E, Z I'AL Am 11 /252,
co n nec t ing ri n g w ith sipho na l membranes a t th e ve n tra l side ,
a -
x 200 ,
b - x 600 .
4. Quenstedtoccras s p ., ZPAL Am 11 /272 ,
int e r ior v iew of th e caecum a nd sip ho n ; x 600 .
D OUVIL. LE, ZPAL Am 11 / 25 1,
connectin g r in g wi th a single sip ho na l m embrane ; x 300.
6. Qucnstcdtoceras s p , juv., Z PA L Am 1/ 30 , siphona l membra ne linkin g the adapertural s u r face of a septu m with th e
5. Qncnstcdt oceras ltenrici R .
siph o na l s u rfa ce : :< 450.
Lukow, Pol and, Jura ssic, C a llo via n
TH E STR UCT UR E AND D E VELOPM EN T OF AMMONITE SH ELL
137
PL AT E 28
I. Quenst edtoceras sp. j uv., Z PA L Am 11/1 70,
med ian sect ion through th e ven tra l wa ll in the pro xim ity of th e attachment of the proseptum and seco nd septum ;
x 2000.
2. Quenstedtoceras sp. j uv., Z PAL Am 11/160,
para media n sect ion through the ven tra l wa ll in th e proximit y of the attachment of th e ca ecum, prosiphon, an d first
2 septa ; x 1000.
3. T he sa me s pecimen,
med ian sectio n th ro ugh the dor sal wall of the initial chamber in the pro ximit y of the a ttachment of the ca ecum a nd
first a nd third septa ; X 1000 .
Lukow, Poland , Ju rassic, Callovian
PLAT E 29
I. Quenstedtoceras sp, juv., ZP A L Am 11/1 60,
pa ramed ian sectio n th rou gh the dorsal wall of the initia l cha mber in proximity of th e a tta chment of the ca ecum a nd
first a nd third septa ; X 2000.
2. The sa me specimen,
section th rough the ventra l wa ll in the pro ximity of th e a ttac hment of the first 2 septa : X 2000 .
3. Qnenstedtoceras sp. j uv., ZPA L Am 11/17 0,
sect ion through th e dorsal wa ll a nd proseptu rn III the pro ximi ty of the a ttachment of the caecum and sipho n ;
x 2000.
Luko w, Poland, Ju rassic, Callovian
PL AT E 30
I. Quenst edtoceras sp. ju v., Z PA L A m 1/29,
section through the d orsa l wa ll, pro septum and thi rd septum in the proximity of the attachment of the caecum a nd
sipho n ; x 1500.
2. Th e same specimen,
pa ra media n sec tion th rou gh th e ventr al wall in th e proxim ity of the a ttac hment of the first a nd seco nd septa ; x 1500.
J . Queustedtoceras henrici R . DOUVILL E, ZPAL Am 1/21 ,
section through the ventra l pa rt of th e thir d septum ; x ISOO.
4. The same specimen,
section th rough the ventra l part of the 7th scptum : x 1800.
Lukow, Poland, Ju rassic, Ca llovia n
P LAT E 3 1
I. Kosmoceras s p., ZP AL Am 11 / 360,
med ian sectio n th rough the ve ntra l wa ll in the pr oximi ty of the attachment of the proseptum ; x 1500.
2. Th e sa me specimen,
d or sal part of the sa me sectio n ; x 1500.
Lukow, Poland , Jurassic, Ca llov ia n
138
C Y PR IAN K ULl CK I
PLAT E 32
1. Quenstedtoceras henrici R . D O UV ILL (" Z PAL A m 1/21,
sectio n thro ugh the ventra l pa rt of the se pta l nec k o f the fifth septurn : y. 3600 .
2. Qucnsredtoceras sp ., Z I'AL A m 1/2 8,
a - sectio n through the d orsal pa rt o f the septa l neck a t the end o f th ird whorl; :< 1200 ;
b - po rtion of the au xilia ry deposit s ; x 3900 .
3. Qttenstedtocera s henrici R . DO UV IL LE, ZPAL Am 11 /3 50,
sectio n throu gh the dorsa l pa rt of the septa l neck o f the las t se ptum precedin g the body chamber; x 1000 .
L uko w, Pol a nd , Jura ssic , Ca llo vian
PLAT E 33
I. Quenstcdt oceras henrici R . D O UVI LL E, Z PAL Am 11 /350,
sectio n through the d o rsa l part o f the septa l neck of th e th ird septum precedi ng the bo dy chamber ; y. 1000.
2. Quenstedtoceras sp ., Z PAL Am 11/ 20,
sectio n throug h the dorsa l part of the se pta l neck o f th e last se pturn sepa ra ting the bo dy cha mber from the phragrnoco ne ; x 600 .
3. Quenstcdtoceras Iienrici R . D O U VIL LE, Z PAL A m I1/3 30,
sectio n throug h th e dorsa l part o f the sep ta l neck o f the seco nd scpturn preced ing the bod y cha mb er; x 1000 .
4. T he sa me specimen ,
sect io n th ro ugh the ventra l part o f th e septa l neck o f the seco nd se ptum preced ing the bo dy chamber ; x 1000.
L uk6w, Polan d, Ju ra ssic, Ca llov ia n
PLAT E 34
J. Kosmoccras sp. , Z PA L A m J1/3 60,
sectio n thro ugh the vent ra l part of the sep ta l neck o f the seco nd scp tum ; x 3000.
2. T he sa me spec imen,
sec tio n through the do rsal part of th e septa l neck o f the seco nd se pt urn ; x 3000.
3. Quenstedtoccras sp., Z PA L A m 11 /20,
sectio n th ro ugh the dorsa l pa rt of th e se pta l neck of th e third septum pre ced ing t he bo dy cha m ber;
4. The same specimen ,
sectio n th rou gh th e dorsa l pa rt o f the septa l nec k o f the seco nd sep tum p receding the bod y cha m ber;
L uk 6w. Pol an d , J u rassic, Ca llo via n
P LAT E 35
I. Kosm oceras sp., Z PAL A m 11 / 360,
sect io n throug h the ve nt ra l pa rt of the se pta l nec k of the third septum ; x 3000 .
2. T he sa me specimen ,
sectio n th ro ugh the do rsa l part o f t he sep ta l neck o f th e th ird sept um : x 3000 .
3. Quenstcdtoceras sp. ju v., Z PAL A m 1/30,
section thr o ugh th e d orsal pa rt of the se pta l nec k o f the th ird sept um ; x 4500.
x 600 .
x 600.
THE STR UCT URl: A ND D E Vl:LOPM EN T 0 1' AMMONITE S HELL
139
4. The sa me s pecimen ,
sec tio n through the ventral part o f the se pta l neck of th e t hird sc ptum : X 4500.
5. Kosmoceras sp., Z PAL Am 11/360,
sectio n through the se ptum a nd ventr al wall o f t he fourth wh orl : x 3000.
6. Po rtio n of figure 5 : x 1000.
Lukow, P ol a nd, Jura ssic, Ca llo via n
PLAT E 36
I. Quenstedtoccras sp. , Z PAL Am 1/30,
median sectio n th ro ug h the dorsal wall a nd proseptum: x 1200.
2. The same spe cime n,
sec tio n th rough th e dorsal par t of t he se pta l nec k in t he midd le of th e fo ur th whorl; A 1200.
3. Qucnstedtoceras henrici R . D OUV ILL E, Z PAL A m 1/ 27,
sectio n throug h the dorsal wall o f t he initi a l c hamber and proscptum, and the attachment of the sipho n and ca ecum ;
x 1800.
L ukow, Polan d , Ju ra ssic, C a llo via n
PLATE 37
I. Kosmoceras sp., Z PA L Am 1/28,
a - secti on through the dorsal part o f the se pta l neck o f a sc ptum of th e the second wh o rl : X 2000:
b - the rel ationship bet ween the di st al pa rt of the se pta l ne ck and to the anteri or a ux iliary deposit s ; x 6000 ;
c - posterior a uxilia ry deposit s; x 6000.
2. The sa me specimen ,
a - sec tio n through the ve n tra l part o f the se pta l neck o f a scpt um of the seco nd wh orl: x 2000;
b - prox ima l part o f a septal neck , a nd th e re lat ion sh ip of a nte rior a nd po sterior au xiliary deposits ; x 6000 ;
c - po sterior au xilia ry deposit s : X 6000.
Lukow , Pol a nd , J ura ssic, Ca llov ia n
PLATE 38
I . Quen stedtoceras sp . j uv., ZPAL A m 1/30,
a - med ia n section t hrough the ventra l wa ll in the proximit y of t he a rachment of the proseprum ; x 4000.
b - median section throug h the ve nt ra l wall in proximity or a ttach me n t o r the seco nd se prum (contin uation or
figure I a) ; x 4500.
Lukow, Pol a nd , J urassic, Call o via n
PLAT E 39
I. Quenstedtoceras sp . j uv ., ZPA L Am 11/ 170,
med ia n secti o n t hro ug h the ve ntra l wall in the pr oximit y o f th e a t tachme nt or the proscptum a nd seco nd sc pt um ;
x 1500.
140
CYP RIAN K ULI C KI
2. Kosmo ceras sp ., ZPA L Am 11 / 360 ,
med ian section through the initial cha m ber and the pr oseprum in the pr oxim ity of the first 2 septa ; x 450.
3. Quenstedtoceras ltenrici R. DOUVll Ll" Z PA L Am 1/ 2 1,
median sectio n through the d orsa l wa ll of the initia l c ha mber a nd proseptum ; X 2400.
4. Kosmoceras duncani (J . SOWERBY), Z PAL Am 1I/l 0 1,
a da pica l surface of a se pturn, with organic membran e pr eserved; x 1800.
Lukow, Pola nd , Ju rassic, Ca llo via n
5. Nautilus pompilius L., ZPAL Am 11 (70, loc. inde t. ,
a da pica l surface o f a se ptu rn, wit h o rgan ic membran e preserved ; x 1800 .
P LAT E 40
I. Holcophyll oceras zignodianum (d 'ORIIIGNY), Z PA L Am 111 /1 ,
port ion o f the med ian sec tion , th e last part of th e sip ho n re mai ning in the bod y chamber ; x 3.2 .
Sa tsis kvile river va lley, Ra tsh a , Ge o rgia, US S R, Ju rassic, Ca llovia n
2. Cadoceras sp ., Z PAL Am 1I1(7 ,
sep ta l neck of the last septurn sepa ra ti ng bo dy chamber from p hragmocone ; x 100.
An a bar river va lley , Siberi a , USS R, J urassic, Ca llo vian
3. The sa me speci men,
septa l neck of the last but o ne septu m, with bot h a nterior a nd posteri o r auxiliary deposit s well developed ; A 100 .
4. SI/rites subanalogus SCHUlGINA, ZPA L Am lIl/ 5,
septa l neck wit h connecting ring , s iphona l membrane a nd bo th anterior a nd posterior a uxiliar y de posits ; x 70.
Baj a rka river va lley , Siber ia , USS R, Cretaceo us, Berriasia n
5. Th e sa me specimen ,
another septal neck ; x lOO.
P LATE 4 1
I. Kosmoceras s p., ZA PL A m 11/ 360,
sectio n through th e do rsal pa rt o f th e septa l nec k of a scptum in th e midd le of the sixth who rl ;
2. Th e sa me s peci me n,
the sa me se pta l neck showing th e st ructure of a nter ior a uxiliar y deposits ; x 6000.
3. The sa me s pec ime n,
the sa me septa l neck showing the str ucture of poste rior a uxi lia ry deposits ; x 6000 .
Lu k6 w, Po la nd , Ju rassic, Call ovi an
A
1500.
PLATE 42
I. Kosm occra s sp., Z PA L Am 1/28,
sectio n pa rallel to th e median onc ; relat ion o f the dorsa l wall o f in itial -chamber to the first 2 sc pta ; x 3000 .
2. Th e same sp ec imen a nd sectio ns, sho wing the rela tio nsh ip of the pr osept um to the ven tral wa ll o f the ini tia l cha mber;
x 2000.
3. Quenstedtoceras henrici R. DOUVlll E, ZP AL Am 11/1 80,
section par allel to the med ian one showing th e relat ion o f the prosept um to the ven tral wa ll o f the in itial cha m ber ;
the nacreo us struct ure o f th e seco nd sept um is visib le ; x 1000.
TH E STRUCT URE AND DEVELOPMENT OF AMMONITE SH ELL
141
4. Quenstedt oceras sp. juv., ZPAL Am 11/170,
secti on parallel to th e med ian o ne sho wing th e rela tio nshi p o f the pr osepturn to the ventral wall of init ial chamber ;
x 1000 .
l.uk 6w , Pol and, Jurassic , Ca llo via n
PLATE 43
1. Quenstedtoceras sp. j uv ., ZPAL Am 1/31 ,
a-d -
section parallel to the medi al one, through th e ventral wall of the init ial ch amber and first whorl; x 600 .
Lukow, Poland, Jurassic, Ca llovi a n
PLAT E 44
I. Quen stedtoccras sp. j uv., ZPAL Am 11/ 311 ,
transverse sec tio n through the initial ch amber and the umb ilical sea m of th e first whorl; a t the left s ide, the sectio n
cuts the nepionic swe lling o f the first whorl ; a t th e right side, it cuts the middle of th e seco nd wh orl; x 1000 .
2. The same s peci me n ,
tran sver se sec tio n through the ve nlra l wall o f the seco nd whorl and the d orsal wall of the th ird wh orl showing the
rela tio nship of the nacreous tissue o f septurn to th e pri sm ati c dorsal wall ; x 1000 .
3. Quenstedtoceras sp . juv., ZPAL Am 1/ 30,
median sec tio n throu gh th e ve ntra l wall o f the in itial c ha m be r ; x 750 .
Luk o w, Pol and , Jura ssic, Ca llov ia n
PLAT E 45
I. Quenstedt oceras sp . ju v., ZPAL Am 1/ 31 ,
nepionic swelling of the vent ra l wall of th e shell ; x 600.
2. Kosm oceras sp., ZPAL Am 1/28,
nepionic swelling o f th e ventral wall of th e shell; x 1500.
3. Quenstedtoceras sp. juv., ZPAL Am I1/1 60 ,
nepionic swelling o f the ve ntra l wall o f th e shell; x 1000.
4. Quenstedtoceras sp . juv., ZPAL Am 11/170,
nepionic swelling of the ventral wall of th e shell; x 1000.
5. Quenstedt oceras henrici R . D OlJVlLLE, ZPAL Am 11/ 50 ,
section parallel to the med ian on e, through the wall port ion o f the init ial ch amber a nd th e first whorl, and through
the nepionic swelling of the dorsal wall ; x 600.
l.uk6w, Poland, Jurassic, Ca llov ia n
PLATE 46
I. Quenstedtoceras henrici R . D a VYIU E, ZPAL Am 11 /300,
longitudinal sec tio n through the ventral wall ; a t the wall th e outer component of the dorsal wall is visible in the
form of pr ominent wrinkl es s it ua ted in pr o xim ity o f the aperture ; x 1000 .
2. Co nti n ua tio n o f figure I ; x 1000.
142
CY P R IAN KU LlCK I
3. C o ntinuat ion o f figure 2 : portion with in bod y chamber; at the left side, t he outer
visible in th e form of an inner pri smatic la yer covering the wrinkles : x 1000 .
4. Conti n uation of figure 3: sectio n in the proxim ity o f t he sc pt urn se pa ra ti ng t he body
bot h compo ne nts of t he dorsal wall arc clearl y visi ble : .< 1000 .
5. Lo ngit ud ina l sectio n through the vent ra l wa ll a nd also t hrough the dorsal wall of
of the penultimate seprum : x 1000.
6. Lo ngitu d in al section through th e ve ntra l wa ll a nd a lso th rough the dorsal wall o f
o f the th ird scptum pr ecedin g the bod y c ha mber :
1000.
Luk ow , Po la nd , Ju ra ssic, Ca llovia n
component of t he dorsa l wa ll is
chamber from the phragmocone ;
the next wh orl, In the pr ox im ity
the nex t whorl , in the proximit y
PLAT E 47
I. Quenstedtoceras henrici R .
2.
J.
4.
5.
6.
7.
8.
DO uv tI.LE, Z PAL Am 11 / 300,
enl a rged po rti on o f th e d orsa l wa ll s ho wn in Plate 24 : 4 : -;' 3000.
Qucnst edt oceras sp, ju v., ~P AL Am 11 /1 60,
lon g itu d inal sec tio n th ro ug h the ve n tra l wa ll : at the wa ll t he o ut e r compo nent of the do rsa l wa ll is visib le in th e form
of dis tinctive wr in kles sit ua ted in proxim ity of th e aperture : :< 1000.
The sa me specime n,
sec tio n sit ua ted a littl e furth e r within the bo d y c ha m ber than figure 2 : - 1000 .
T he same specime n,
sec tio n s itua ted a little further wit hin the bod y c hamber th an figu re 3: in th e o ute r pri smatic la yer o f ve nt ra l wa ll
a d isco nt in u ity is visi ble; >: 1000 .
The sa me specimen,
sec tio n situ ated a lit tle further wi th in the bo dy chamber th a n in figu re 4: t he wr inkles a rc lin ked a t the ba se ; /" 1000
The sa me s pecime n ,
sec tio n situa ted a little furt her wi thin t he bod y ch amber t han in figur e 5 ; in the o ute r pri sm atic la yer of ve nt ra l wa ll
a di scontinuity is visib le wh ich d oes not continu e into the nacre o us la yer ; .< 1000.
T he sa me s pec ime n,
sectio n sit ua ted a littl e furth er with in th e bod y c hamber t ha n ill figure 6 : t he d iscon tinuity is marked in bot h the
outer pri smatic a nd nacre ou s la yer s ; >, 1000.
T he sa me spec ime n,
sec tio n s it ua ted just an tcri o ry to the last sc pt um ; s pac es a mo ng th e interco nnected wrink le tops a re filled by inner
pr ism a tic tissu e ; >: 1000.
Lu kow, Pol a nd , Jura ssic, Callo via n
PL AT E 48
I. Quenstedtoceras s p. j uv., Z PAL Am 11 / 312,
2.
3.
4.
5.
G.
tr an sverse sec tio n th rough th e ve nt ro la te ra l wa ll ar the bound ar y between the end of seco nd whorl a nd the beg in n ing
o f t hird whor l; a nd t hroug h th e lat er al wa ll of t he next wh orl a t t he u m bilical sea m ; x 600 .
Qnenstedtoceras sp . juv., Z PA L Am lI fJ 11 ,
um bil ical sea m betw een th e second a nd th ird whor ls ; x 1500.
Kosmoceras duncani (1, So w .), Z PA L Am lI jl Ol ,
ve ntral wall of th e first whorl, covered by t he dorsal wall of th e next whorl ; x 360.
T he sa me spec imen,
vent ral wall of t he seco nd wh orl, visible when t he d orsal wa ll of th e next wh orl is partly remo ved ; x J60.
The sa me s pecime n,
d o rsa l view of the seco nd whorl in the pr o ximity of t he umbi lica l sea m : x 1800.
Qucnstedtoceras henrici R . D OU VI L LE, Z PAL A m 11 / 252,
th e re la tion shi p betwee n t he nac reo us tissue of seco nd sc pt um a nd th e ve n tr a l wa ll : >: 4500 .
L uko w, Po la nd , J ura ssic, Ca llo viuu
Palaeontologia Polonica, No . 39, 1979
C.
K ULl CKI: TIl E STRUCTURE Al'D DE\' ELOPMEl'T OF AMMONITE SHELL
PI. 2+
PI. 25
Palaeontologia Polonica, No. 39, 1979
C.
K ULl CKI : THE STRUC T URE AND D EVELOPM ENT
or
AMMONITE SHELL
Palaeontologia Polonica, No. 39, 1979
3a
C.
K ULI CKI :
Tus STR UCTURE AND DEVELOPM ENT OF AMMONITE SHELL
PI. 26
Palaeontologia Polonic a, No. 39, 1979
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K ULlCKI: TH E STR UCTURE AND DEVELOPEMNT OF AMMONITE SHELL
PI. 27
PI. 28
Palaeontologia Polonica, No. 39, 1979
c. K ULl C KI :
TH E STRUC TU RE AND DEVELO PMENT OF AMMONITE SHELL
Palaeontologia Polonica, No. 39, 1979
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K ULl CKl : THE STR UCT UR E AND DEVELOPMENT OF AMMONITE SHELL
PI. 29
PI. 30
Palaeontologia Polonica, No. 39, 1979
C.
KULI CKI:
Tu z
STR UCTURE AND D EVELOPME NT Of AMMONITE SHELL
Palacontolog ia Polonic a , No . 39, 1979
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K ULl CK I: THE STR UCT UR E AND DEVELOPMENT OF AMMON ITE SHE LL
PI. 31
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K ULlCKI: T HE STRUCTURE Al\D DEVELOPMENT OF AMMONITE SHELL
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PI. 33
PI. 34
Palacontologia Polonica, No. 39, 1979
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K ULl CKI : TH E S-:- RUCTU RE AND DEVELOPMEl'T
or
AMMOl"IT E SHELL
Palaeontologia Polonica, No. 39, 1979
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K ULlCKI: THE STR UCTURE AND DEVELOPMENT OF AMMONITE SHELL
PI. 35
PI . 36
Palacontologia Polonica, No. 39, 1979
C.
K ULlCKI :
Tnt
STRUCTUR E A1':D DE\'E LOPlIIE1':T OF AMMONITE SHELL
Palaeontologia Polonica, No. 39, 1979
C.
K ULIClU : THE STRUCT UR E AN D D EVELOP~lENT OF AMMONIT E SH ELL
PI. 37
PI. 38
Palaeontologia Polonica, N o. 39, 1979
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K ULl CKI : T H E STR UCT UR E AND DEVELOPME:"T
or
AMMONITE SHELL
PI. 39
Pa'acontolaeia Polonica, No . 39, 1979
C.
K ULlCKI:
Tut
STRUC TU RE A:"D DEVELO PMEl\1
or
A~IMO~ ITE SHELL
PI. 40
Palaeontologia Polonica, No. 39, 1979
C.
K ULlCK.I:
Tn t
STRUcrURE Al'D D EVELOP~IE:-;T OF AM.\IO:-lITE SHELL
Palaeontologia Polonica, No. 39, 1979
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KUUCKl: THE STRUCTURE AND DEVELOPMENT OF AMMONITE SHELL
PI. 41
Palacontologia Polonica, No. 39, 1979
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K ULlCKI: TH E STRUCTURE Al' D DEVELOPEMNT OF AMMONIT E SH ELL
PI. 42
Palaeontologia Polonica, No. 39, 1979
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K ULICKI: THE STRUCTURE A:'olD DEVELOPMENT OF A\lMONITE SHELL
n .4:5
Palaeontologia Polonica, No. 39, 1979
PI. 44
C.
KULlCKI : THE STRUcruRE AND DEVELOPMENT OF AMMONITE SHELL
Palaeontologia Polonica, No . 39, 1979
Pl.45
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THE STRU CTURE AND DEVELOPMENT OF AMMONnE SHELL
PI. 46
Palaeontologia Polonica, No. 39, 1979
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KULlCKI: THE STRUCTURE AND DEVELOPMENT OF AMMONITE SHELL
Palacontologia Polonica, No. 39, 1979
PI. 47
c. KULICKI:
THE STRUCTURE AND DEVELOPMENT OF AMMONITE SHELL
PI. 48
Palaeontologia Polonica, No . 39, 1979
c. K ULl CKI:
THE STR UCTUR E AN D DEVELOPMENT OF AMMONITE SHELL