Tooth development in East African Paranthropus

FernandoV. Ramirez- Tooth development in East African
Paranthropus
Rozzi
et
Chaire dePaléoanthropologie
préhistoire,CollègedeFrance,I I, pl.
Marulin Berthelot,75(N5 Pans,
France
"hyper-thick" enamel was
A rapid differentiation rate in enamel with a
suggestedto represent a synapomorphic condition in Paranthropusspecies.'1o
check this hypothesiswe have analysedthe enamel microstructure ofmolar
teeth lrom Shungura Formation (Omo, Ethiopia) attributed, by teeth
Received 14 October l99l
and P. boisei.The number, course and angles
macrostructure , to P. aethiopicus
October
1992
Revision received9
ofthe enamel dentine junction ofstriae ofRetzius and the relative importand acceptedl5 October 1992
ance ofcuspal and cervical stageswere analysed with a stereomicroscope.We
assumedthe striae of Retzius are growth markers with a 7-day periodicity.
K e1uords: striae of Retzius,
Thus,
the features analysed indicate the time ofcrown formation, the number
Paranthropus
athiopicus,
Paranthropus
ofameloblastsactive at any one time, the differentiation rate and the relative
àolsel,crown formation.
importance of the number of ameloblastsactive at any one time in relation to
the overall number of ameloblastsimplicated in the total crown formation
respectively. Enamel thickness was also measured. Although overlap was
lound between some characteristics, it was possible to define dissimilar pathways in tooth development. Paranthropusaethiopicus,with a faster differentiation rate and a greater number of ameloblastsactive at any given time,
have a shorter time of crown formation than P. boisei.At first it seemsthat
hyper-thick enamelis not presentand that ameloblastsoperate as a whole. In
groups. Thus, ifthe selectionto
P. boiseithe ameloblastswork as successive
species,as
form teeth quickly and the synapomorphic featuresin Paranthropus'
would be more specialized than P. boisei.
suggested,are retained, P. aethioperzs
Journal of HumanEuolution(1993) 24, +29-45+
lntroduction
Grine & Martin ( l9BBa,ô)have suggestedthat a rapid differentiationrate with large numbers
"hyper-thick" enamel
of ameloblastsactive at aîy one time establishesthe hopnologyof the
"hyper-thick"
enamel rep(Martin, l9B5), and that the rapid differentiation rate with the
species.These authors predict the samefor
resentsa synapomorphy shared by Paranthropu.ç
and estimate that this kind of information would confirm its specific
aethiopicus
Paranthropus
status.
To check Grine & Martin's prediction for'P. aethiopicus'toothdevelopment in order to
establisha possibletrend in the pattern ofcrown formation in EastAfrican Paranthrlpusand to
boisei,we have
is the ancestorof Paranthropus
determine whether in fact that P. aethiopicus
in
molar
teeth from
thickness
microstructure
and
enamel
enamel
analysedsome aspectsof
'rr '
(Ethiopia).
formation,
Omo
site
Shungura
. . , . : .
i "
Paranthropusaethiopicus andParaîthropusboisei
Taxonoml.The presence of robust Australopithecines at 2'5 Myrs in East Africa was
by Arambourg & Coppens(1967,t968; Coppens,1970)from one mandible (Omô
suggested
1B)
found
in Member C of Omo Group. This presencereceivedmore acceptancewith tbe
I Bskull
WT t 7000 (Walker etal., l9BG).The disagreementarisesin the taxonomic
discoveryof
attribution.
Walker & Leakey (l9BB; Walker et al., 1986; Leakey & Walker, 19BB)interpret the
i.e., Omo I B-I B, WT I 7000,asprimitive
characteristicsof earliestrobust AustralopitheÇines,
on
but in the range ofP. boiseivariation.Nevertheless, analysingWT 17000and comparing it
with other Plio-Pleistocenehominids,Kimbel etaL (l9BB) found that only two out ôf32 traits
+ 26 $08.00/0
0047 2+841931060429
O 1993Academic PressLimited
430
F. V. RAMIREZ-ROZZI
Figure l. Occlusal view of Omo 33-6172showing that thc broken surlace in mesial face is vertical and
peipendicular to the enamel dentinejunction. Lateral laccsspeciallylingual and buccal lacesarc bulbous
à.J li-it u nurrow occlusallace.At'cessorycrestsdo not presentan important development.Wear in mesial
edgeis approximarcly asimporrant asin protoconid indicating that mesialedgeis quitc ashigh as the cusps.
-l'he
bar correspondsto I mm.
concludedthat thereis little ground for includingWT 17000in
aresharedwith P. boisei.They
speciesin East Africa is
The distinction betweentwo robust Australopithecines
P. boisei.
Coppens,1967,l968),
(Arambourg
&
supporredby a largenumber of studieson mandibles
(Holloway'
l9B8), premolar morfacesand cranial bases(Kimbel el al., lgBB), endocasts
The
joint
(Picq, 19904,ô).
morphology
phology(Suwa,1988,1990)and temporomandibular
from
the
l9BB)
et
al.,
1986;
Kimbel
(Walker
al.,
et
name given to this speciesis P. aethiopicas
(
first descriptionby Arambourg & Coppens 1968)'
Molar teethdffirentiation.The first appearanceof P. boiseiin Omo Group is from Member E
( B o a z ,l 9 7 7 ; C o p p e n s ,1 9 7 5 ,1 9 8 0 ,l 9 B 9 ;D e l o i s o n ,1 9 8 6 ;H o w e l l & C o p p e n s ,1 9 7 3 ,1 9 7 4 ,
1976;Howell & Wood, 1974)at 2.4 Myrs (Feibelet al., l9B9) or from Member D (Grine,
from
1985) at 2.5Myrs (Feibelet at., 1989).The taxonomy of robust Australopithecines
teeth
robust
All
was confirmed.
Omo was reconsideredwhen the existenceof P. aethiopic,r.t
from Members E and F of Shungura Formation has been attributed to P. aff. aethiopicus.
Suwa (1990) recognizesrobust premolarsfrom Members C and D which he attributesto
He finds some differencesin robust premolars from Members E and F and
P. aethiopicus.
Robust premolarsfrom Member G were assignedto P. aff'
reports them to P. atr.aethioplras.
aethiopicus
I boisai(Suwa, I 990).
Comparisonof robustmolarsfrom Member C to Member G of ShunguraFormation (n:
42 lower molar and n:27 upper molar), carried out by direct observation,enablesrecognition of two groupsof teethfrom their macromorphology.Group A comprisesmolarswith a
strongbucco-lingualdevelopmentat the cervix with a narrow occlusalfacewhich appears
well developedmesio-distally(FiguresI and 2). It is accompaniedin the upper molarsby a
PARANTH
ROPUS TOOTH
DEVELOPMENT
431
Figure 2. Occlusal view of Omo 57.6-2+4.Lingual lace is almost completely visible in occlusal view.
Acccssorycrestsart very short and single.The bar correspondsto I mm.
very oblique lingual face from the cervix to the apical area. The lingual face is almost
completelyvisiblein the occlusalview. In the lower molars,very bulbousbuccaland lingual
facesexplain a narrow occlusalfacewith a strongbucco-lingualdevelopmentat the cervix.
The mesialand distal edgesare high and almostcompletelyhide the epicrestsin the mesial
crestsare either nonexistantor singleand short.The groovesare
and distalviews.Accessory
deep and limit rounded cusps.The enamelbridge is almost missing.The teeth of group B
presenta strong bucco-lingualdevelopmentat the cervix which is seenalsoin the occlusal
àce (Figures3 and 4). The cuspsare morespacedout than in molarsofgroup A. The lingual
face runs straight from the cervix to the apical area in upper molars and lateral facesare
almoststraightin lower molars.The mesialand distaledgesare lower and revealan importand accessory
in the mesialand distalviews.The epicrests
ant part of the cuspsand epicrests
"fiII" in the occlusalface.The mesio-distalgrooveis shallow;
crestsare well developedand
almosrall the othergroovesaresimilar.The enamelbridgeis alwayspresentin uppermolars.
Group A molarscomefrom MembersC to F and thoseof group B from MembersE to G.
Robust specimensfrom East Africa as ancient as those of Members C and D have been
while robust specimensfrom 2 Myrs deposits,including Member
attributed to P. aethiopiczs,
and
G, were reported to P. boisei.Thus, we have assignedmolars of group A to P. aethiopicus
thoseofgrou p B to P. boisei.
I
tructureof ename
M icro.c
and the striaeof Retziusmake it possibleto
in
enamel,
the cross-striations
structures
Two
(see
Mann etal., 1990b,for a wider discussion).
of
tooth
development
aspects
elucidatesome
(Figure5), seenin scanningelectronmicroscopy(SEM),
The cross-striations
Cross-striations.
dark and light bandsof prismsfrom the enamel-dentinejunction(EDJ)
appearassuccessive
432
F. V. RAMIREZ-ROZZI
l'ieure 3. Occlusal view of Orno 76-37 showins that thc broken surlh<'e of mesial lacc is rertical and
p c r p c n d i c u l a r t o t h c e n a m c l - d c n t i n e j u n c t i o n . L a t c r a l f à c e sa r c n o t b u l b o u s . S t r o n g w c a r i l t b u c c a l c u s p s i s
;rccompanicd by a slight wear in mesial edge bringing to the lirre that the mesial edgc is lorter thatr tht'
cusps.'l'he bar corresponds io I mm.
to the enamel surlàce (Risnes, l986). The varicosities,successivefine transverseenlargements
and constrictions ol'diameter ol'prisms, are related to cross-striations(Boyde, 1964, 1976r.
Boyde ( 1979) suggeststhat the cross-striationsare caused by a variation in the local concenrrarion of COr. Simmelink & Nygaard (1982) suggest that the size of crystals could produce
the difference in the prism surface. Warshawsky & Bai (1983; Warshawsky el al., 1984t
suggestit results from the spiral arrangement ofthe crystals.
The interpretation of cross-striation differs; some authors consider them to be a simple
geometry of enamel structure, others relate them to daily incremental enamel apposition.
Warshawsky et al. (1984) believe that there is no proof of periodicity in the prism struc"Unless
that the spiral arrangement of crystallites is under circadian control. . . ."
ture
(Warshawsky et al., l9B4:252').
B o y d e ( 1 9 6 4 , 1 9 7 6 , 1 9 7 9 ) p r o p o s e st h a t t h e v a r i a t i o n i n t h e l o c a l c o n c e n t r a t i o n o f ' C O o i s
originated by' circadian modifications in the appositional rate of ameloblasts (see Dean,
1987a, 1989, for reviews of literature). The size of cross-striationsmatches the results produced by appositional rate studies from experimental analyses (Schour & Poncher, 1937;
'fhe
between prism length
relati<-rnship
Schour & Hoffman, 1939; Massler & Schour, 1946).
and time formation (Risnes, l986) supports the view that cross-striationsoccur as a circadian
phenomenon.
PARANTH
ROPUS TOOTH
DEVELOPMENT
+33
!'igurc 4. Occlusalvieu ofOmo 33-65.Occlusal laceis aslarge as thc bascof thc crown. Accessorycrestsare
"fiII" in the occlusalfacc. Thc bar corrcspondsto I mm.
wcll dcr,clopcdand
Perikymata
Striae of
Retzius
l'igure 5. Schcmaticrepresentationofincisor buccolingualsectionshowing incrementalgrowth-markersin
enamel. The most common interval bctwecn adjacent striae is sevcncross-striationsand it is constant in
'l'he
striaeofRetzius arrivins at the enamel surfaceproduce perikymata (after Bromage &
eachspecimen.
D c a n .l 9 B 5 ) .
434
F. V. RAMIREZ-ROZZ I
lNo. sR l-..-*
r_-.- I
I rïr,nu,,on I
Differentiation
rate
No . of secretor
ameloblastes
No . of cuspaland
cervical SR
Cuspal and cervical
heieht ratio
Successive outlines
during crown formation
Relative importance
of crown's
Figure 6. From the analysisofgrowth line features (left), characteristicsofenamel formation can be
deduced and the pathways ofcrown development estimated (right). Arrows indicate the relationship
betweenstria featuresand pattern in tooth development. SR:striae of Retzius; EDJ:enamel-dentine
junction.
Striaeof Retizrs.The striae of Retzius are lines which run acrossthe enamel in radial sections
(Figure 5). They can be seenin SEM (e.g.,Boyde, 1970;Frank, l97B; Weber & Ashrafi,
1979)or with a light microscope(e.g.,Weber etal.,1974;Risnes,l9B5) wherethey are easily
visible becauseof differencesin colour or birefringence in polarized light. The striae of
Retzius are produced by a marked deviation in prism disposition (Gustafson& Gustafson,
1967;Osborn,1973;Boyde,1976;Weber & Ashrafi, 1979;Boyde& Martin, l9B4) and/or by
a changein the ratio betweenorganic and inorganic phases(Gustafson& Gustafson,1967;
Boyde, 1970;Frank, l97B;Boyde& Martin, l9B4).
someworkerspresentthe striaeofRetzius assimply enamelstructures
Like cross-striations,
while others see them as a manifestation of a repetitive, systemic and regular perturbation of tooth development(Newman & Poole,1977).Goldberg(1982)considersthe striae
as vanishing planes of organic material of enamel without any periodicity in tooth
development.
According to Boyde ( 1964)and Shellis( l9B4), the striaeof Retzius indicate the successive
positions of the matrix-forming front through the crown's formation from cusp to cervix
(Figure 6) . Boyde ( 1964)hassuggestedthat the differentiation rate of ameloblastsis reflected
in the angle ofintersectionofstriae ofRetzius with the EDJ. Where the rate is rapid the striae
form a smaller angle with the EDJ than when it is slow. The numbersof ameloblastsactive at
any one time is deduced by the courseof striae. The number is greater when the striae run
along a great proportion of the tooth height. The most common number of cross-striations
betweenadjacent striae is sevenor eight (Bromage & Dean, l9B5; Newman & Poole, 1974;
Shellis& Poole,1977;Dean,l9B7a;Beynon& Reid, l9B7) (Figure5) so the striaeof Retzius
representa near weekly, repetitive, regular and systematicdisturbance whose aetiology is
unknown (Newman & Poole, 1974;seeDean, 1987a,1989,for reviewsof literature) . Teeth
crowns can be divided into two stagesupon the striae of Retzius arrangement (Beynon &
Wood, l9B7) (Figure 7). In the first or cuspal stage,the lines of Retzius do not reach the
enamel surface, they involve successivelayers of appositional enamel. In the second or
cervicalstage,the linesofRetzius presentan imbricational position; they run obliquely from
PARA NTH R O PUS TOOTH
SR1
+35
DEVELOPMENT
SR1
o
d)
d
o
O
Figure 7. Crown stages'height. We have estimatedthe height ofthe cervical and cuspalstagesto establish
the relative contribution ofeach one to the height ofthe crown. It was measuredon a line from the dentine
horn to the cervix (H-Hr) perpendicular to another line connectingthe cervix of oppositefaces(C-C'). The
point ofintersectionbetweenthe first cervicalstria and the enamel-dentinejunction was projectedon H-Hr
(i) parallel to C-Cr. hCu : height ofthe cuspalstage;hCe: height ofthe cervical stage;SR I : first cervical
stria.
the EDJ to the enamel surfacewhere they produce the perikymata (Risnes, l9B5; Dean,
l9B7a) (Figure5).
The associationbetween cross-striationsand enamel appositional rate has not been
demonstrated precisely (Mann et al., 1990b)but this associationhas never been seriously
questioned (Dean, l997a). For the present study we have followed the circadian and
circaseptaninterpretation of cross-striationand striae of Retzius.
grluth markers.Cross-striationsand the striae of Retzius, as incremental growth
Incremental
markers, have been used over the last few years to understand some aspectsof tooth
developmentin hominids.
The countsof cross-striationsand the striae of Retziusor perikymata was usedto estimate
ageat death (Boyde, 1963;Bromage& Dean, l9B5; Dean elal., 1986;seealsoBeynon & Reid,
1987;Bacon, l9B9) and the time of crown formation (Beynon & Dean, l9B7; Beynon &
Wood, 1987;Stringereta\.,1990;Mann etal., 1990a;Ramirez-Rozzt,l99l). Thesegrowth
lineswere usednot only to estimatethe time ofcrown formation in hominid teeth but also to
recognizethe differentiation rate and the number of ameloblastsactive at any one moment.
Most of the analysisof growth markers in fossilswas carried out on teeth attributed to
arapid timeformation
(seeDean,19BB).Beynon& Wood (1987)havesuggested
Paranthropus
for molar teeth ofP. boisei(2.12-2.59years).This was in agreementwith the resultsproposed
by Dean (1987b), who obtained them by counting perikymata on incisor teeth and matching
them with calcificationstageson M l. For premolars,Beynon & Dean (1987)have estimated
at2-4years the time of crown formation for one premolar of P. boisei.These resultssuggest
shorter than in the
that the time for crown formation in premolarsand molars of P. boiseiwas
formation implies
a
rapid
crown
P.
achieved
by
which
boisei
The
mechanism
modern human.
number of
and
a
greater
(1986)
Beynon
&
Wood
rate
as
proposed
by
a rapid differentiation
436
F. V. RAMIREZ-ROZZI
ameloblastsactiveat any one time (Dean & Wood, l98l;Beynon & Wood' l9B7; Grine &
Martin, I99Ba,b).
The distance
Some differenceswere observed between distinct speciesof Paranthropus.
is greater than in Homo
between perikymata near the cervix on incisors of Paranthropzs
sapiens
as a consequenceof the rapid differentiation rate (Bromage & Dean, l9B5). But the
perikymata-packing pattern of P. boiseiis not the same as the South African Paranthropus
[Dean, 1987ô;Grine&Martin, tgBB] (theseauthorsdistinguishP.robustusandP.crassidens)f.
showing that the
The perikymata are closerin P. boiseithan in South African Paranthropu.r
differentiation rate could be more rapid even in the latter.
Materials and methods
The analysisof growth markers and enamel thicknesswas made on eight teeth. The sample
Omo 84-100 (lower RM2), Omo 57'6-244
consistedof four teeth attributed to P. aethiopicus:
( u p p e r R M 2 ) , O m o 3 3 - 3 3 2 5( u p p e r L M 3 ) , O m o 3 3 - 6 1 7 2( l o w e r R M 3 ) ; a n d f o u r t e e t h
Omo 33-65(upperLM3), Omo76-37 (lowerLM3), Omo 141-l (upper
assignedto P. boisei:
teeth are from Member C,
aethiopicus's
RM3), Omo l4l-2 (upper LM2). Paranthropus
2.85 Myrs to Member F,2.34 Myrs (Feibeletal.,l9B9); thoseofP. boiseicomefrom Member
F and Memb er G,2'34 and 2'32-l'9 Myrs respectively(Feibeletal., l9B9).
Theseteeth presentnaturally broken surfaces.Six out ofeight specimensshow their broken
surfacesflat, running straight from cusp to cervix with perpendicular orientation to EDJ. In
some teeth, to avoid possiblea priori variations between lateral faces,some characteristics
were analysedon a different broken surfaceto that where the count of striae of Retzius was
carried out. The methodology usedenablesto count striae in different faces,the number of
striae not being influenced by variations betweenfaces(seebelow). Striae were counted on
the lingual faceofomo 33-6172,inthe distal àce ofomo 76-37 andin the mesialfaceofomo
84-100;meanwhileother characteristicswere obtained on their mesialface (FiguresB and 9).
Characteristicswere analysedin the buccal faceofomo 33-3325and Omo l4l - I (Figure 10),
in the distal àce of Omo l4l-2 and in the lingual face of Omo 33-65. The number and
characteristics of striae were obtained in the lingual face of Omo 57'6-244; other
characteristicswere measuredon its buccal face (Figure I I ).
Obseruation
(Leica) fitted with a central rotatable
The teethwere observedwith a zoom stereomicroscope
Polarisationstageand with a length measuredigital ocular connectedto a calculator-meterprinter RZD-DO (Leica). The surfaceswere illuminated obliquely by a 6V 120W halogene
light source.
The fractured surfaceswere orientated perpendicular to the optical axis of stereomicroscopeenabling accurate measurement.To obtain optimal visualization of striae, the teeth
were rotated with the rotatable stageand the light sourceremained fixed. We have found
that the striae are bestvisiblewhen only one light sourcecomesfrom the EDJ and the cervix.
The striae of Retzius were more evident when the specimenswere immersed in ethanol
(Beynon & Wood, l987), but the exceptionalconditionsof fossilizationenabled us to seethe
striae even without ethanol and polarized light.
Features
The broken surfaceanalysiscomprisethe lateral enamel thickness,the count and the course
ofstriae, the slopebetweenstriaeofRetzius and EDJ, the number ofcuspal and cervicalstriae
PARA NTH RO PUSTOOTH DEVELOPMENT
l'ierrn 8..\lesial liirctureol ()nrolJll-6172 ste ligurcl3.'llrt
437
barcorrt'spttndsto0itmm.
and thc crou'n lrcight rlrtio o1'cuspal and ccn'ic:rl stages. .'\ll values lr:rve been obtained
directlv bv obscn'ingoriginal material.
.\.untht oJ'.tlriueoJ'Ret;iu.r.I n previous works the total number ol'striae rvas calculated liom a
s m a l l n u r l l t e r o l ' s t l i a e t l J e v n o n& D e a n , l 9 8 7 ; o r t h e t i m e o l ' c r o w n l i t r m a t i o n w a s o b t a i n e d
lrv cotrntirrg onlv sorre striac (Brom:rgc & Dean, l9B5; Dcan et aL., 1986; Stringer el al., 19901'
\ l a r r r r 1 1a 1 . .1 9 9 0 a :R a r n i r e z - R o z z i , l 9 9 l ) . U n l i k c t h e s ew o r k s , t h c e x c e p t i o n a lc o n d i t i o n o f
t l r e t e e t h h a s n t a c l ei t p o s s i l r l et o s c t ' a l l t h e s t r i a e . l t h a s e n a l l l e d u s t o o b t a i n t h e t o t z r lt t u m b e r
o f ' s t r i a ei n t . a c ht o o t l ) l ) \ ' ( ( ) u n t i n g t h e m o n e b v o n e . Â t t e n t i o n u , n sl i r c u s e do n a l l g r o w t h l i n c s
c o u n t e d . s o n e h a v e s t ' l c c t e dt h e l r r o k e n s u r l à c ew h i c h p a s s e sc l o s et o t h e d c n t i n e h o r n . T h c
f i r s t m i n e r a l i z a t i o n s t a g e w : r s r c p o r t c d t o t : r k c p l a c e i n t h c m c s i a l c u s p si n m o d c r n h u m a n s
( K r a u s , 1 9 6 3 , , t h u s t h c I r a c t u r e p l a n e s i t u : r t e do n t h c m e s i a l c u s p s w a s c o n s i d e r e dl o r t h e
c o u n t i n s . N e v e r t h e l e s st,h e l o r m a t i o n o { ' t h em e s i a lp : r r t o l ' a t o o t h f i n i s h e se a r l i e r t h a n t h a t o l t l r e d i s t a l p a r t a s i n d i c a t e d b v p e r i k v m a t a c o u r s e si n P a r a n l h r o p a(,pr e r s . o b s . ) ; s o : r m e s i a l
Iiactured planc docs r)ot in('ludt' the last stri:re :rnd their total number is misleading. The
periktmat:r corrcsponding to thc last stria counted or-rthc broken sur{àce was identified and
'l'he
perikvmata pl:rced cervically to it were
its course lollowed on the presen'ed tooth laccs.
counted and added to the Irumber ol'striae.
'l'he
t o t a l n u m b e r o l ' s t r i a e m a d e i t p o s s i b l et o c s t i m a t e a n a ( ' ( u r a t e t i m e l b r c r o w n l b r between adjacent striae rzrnges{iom six to
mation (Figure 61. The number ol-crr-rss-striati<,rns
438
F. V. RAMIRE,Z-ROZZ,I
I'igurc 9. \lt.sial liacturc of ()rno 76-37 i srt l'igun
l ll . I hc bar t orrcspotttlst() I tttr)1.
n i n c l t en v c c n i n d i v i d u a l s a n d i t i s p o s s i b l ct l r : r t i t ' u ' a r i c sf r o m o n e s p e c i c st o a n o t h er . , \ s c r o s s s t r i a t i o n s\ \ , e r cn o t s e e ni n o u r n t a t c r i : r l i t i s i m p o s s i l t l ct o t e l l l l t c t t u m l l c r o l ' c r o s s - s t r i a t i o t t s
So rve must assumetlterefrlre:r
,tlcl lt. boi.çei.
lretrteerracl.jacentstriae varied liom P. aethiofticu.t
h
a
vt'assumed a 7-da1 inten'al
\
\
'
e
s i m i l a r n u m b e r o l ' d a 1s l t c t w e e n s t r i : r ci n t $ , o s p e c i e s .
. c p r e s c n ta l s o t h c
| c t n e e n a d j a c e n ts t r i a ea s t h i s i s m o s t o l ï c n c i t e d i n t h e p u b l i s h e ds o u r c e s W
r.ari:rtic.r1of t'rou,n time f'ormation I'or a range six to tritrc cross-striationsllctwectr adjaccnt
striae.
'l'he
(,lour.çe
ul'Retziu.ç. optimal visualization ol'striae has providcd arl accurate identi{ioJ'.çtriae
t : a t i o n o l ' s t r i a ' sc o u r s u . ' l ' h el i a c t u r e d p l a n e o l ' l a t e r a l t o o t h l à c e sw a s d i v i d e d i n t h r e e a r e a s :
'['he
courseol'striae was defirted fbr each area and coustructed ott
cuspal, central and cen'ir:al.
a section for each lateral fàce analYsed.
The direction ol'striae shows the succcssiveoutlines of :r crowtr growth during its fbrmation
and the letrgth ofstriae make it possil;leto dedut'e the relative numl-ler of'activt'amelolllzrstsat
a n y o n e t i m e ( Fi g u r e 6 ; .
. l n g l t . s t r i a e o f R e tE
1 iDuJ, r. L s d e f i n e d b y B e y n o n & \ \ ' o o d ( 1 9 8 6 ) , t h e a n g l e o f t h e s t r i : r r v i t h
the ED.Jwas measuredbetweenthe tangent to F)DJand the tangentt()stria at their poirtt ol
PA RA NTH RO PUS TOOTH DEVEI,OPMENT
+39
'l'hc
c o u r s co [ ' s t r i a cc h a n g c s
F i g u r c 1 0 .B u c c a ll r a c t u r co f O m o l 4 l - 1 , u p p c r R M 3 a t t r i b u t c d r c P . b o i s e i .
b
P
.
a
c
t
h
i
o
l
t
i
z
. ru t t h e , vh a v c t w o d i f l è r e n t
n
o
t
r
o
u
n
d
c
d
a
s
i
n
a l o r r gt l r t ' l a t c r a l f à c e . ' I ' h cc u s p a ls t r i a c a r c
'l'ltt'
b : r r t o r r c s t r o n dtso 0 ' 5 m m .
dirrt tions.
intersection. The angle was taken in the three areas of fractured plane. For each area five
angles were measured on three separate occasionsand the mean of all measuresmaintained.
The angle stria-EDJ makes it possible to visualize the position of the advancing matrixIbrming front, so it allows us to interpret the differentiation rate of ameloblasts
(Figure 6; . Thc measuresin the three areas of each tooth enable us to observe the changes in
differentiation rate as the processof crown lormation proceeds.
'lhe
first stria which arrives at the enamel surface was
.Ifumber oJ cuspal and terttical .çtriae.
striae
in cuspal and in cervical stage. The ratio of cuspal
identifiecl to obtain the number of
and cervical striae was calculated.
The number ofstriae in cuspal and in cervical stage allows us to estimate the time ofcrown
formation of each one and to establish the relative importance of cuspal and cervical parts in
time of crown formation (Figure 6).
Crown height ratio of cuspaland ceruicalstages.'lhe crown height was determined for a vertical
line drawn from the dentine horn to the cervix and perpendicular to a line connecting the
cervix of opposite faces (Figure 7). The point where the first cervical stria contacts the EDJ
440
F. V. RAMIREZ-RO7,7,1
l i e u r e l l . L i n g u a l l i a c t u r c o l ' ( ) m o 5 7 . 6 - 2 4 { . u p p e r R \ l 2 a r t r i l l r t c c l t o l ' . a c l h i o ! i r u t . l l t t t o L t r s to l ' a l l s t r i a e
i s h o m o g c n c o u s . ' l ' h c s t r i a c a r ( ' ( ' o l ) ( : l \ ' ( ' b u t l e s st l r a r r i n l o r x ' r n t o l a r s . ' l h t ' b : r r t o r r t ' s l x r I t d s t r t ( J 5 n t t n .
'l'hen
the ratio ol'
w:rs pro.jectedon the vertical line establishing the limit in height o1'stages.
h
e
i
g
h
t
w
e
r
e
c
a
l
c
u
l
a
t
e
d
.
cen'ical and cuspal
,,\s the number o1'striae bv stage, the ratio of' cervical and cuspal height provides atr
l nd imbricational crown's parts (Figure 6 .
e s t i m a t i o no f r e l a t i v e i m p o r t a n c e o { ' a p p o s i t i o n a a
The hcight of each stagc is rclated to the stri:re'scoursc.
'I'he
l a s t t w o f è a t u r e ss h o u ,t h c r c l a t i v c i m p o r t a n c e o 1 ' t h cn u m b e r o l ' a c t i v t ' a m e l o b l a s t sa t
a n v o n e t i m e i n r e l a t i o n t o t h e o ' u ' e r a lnl u m b e r o l ' a m e l o b l a s t si m p l i c a t e d i n t l t e t o t a l t ' r o n t t
l i r r m a t i o n . r \ t o o t h w h e r e t h e c u s p a l s t a g eh a s a h i g h h c i g h t r a t i o m e a n s t h i i t t h e : r m e l o l t l a s t s
o p e r a t e r a t h e r a s a w h o l e ; a t o o t h w h e r c t h c c er v i c a l s t a g ch a s a h i g h h e i g h t r a t i o i m p l i e s t h a t
the ameloblasts work rather in successivegroups.
oJ'enamel.Linear measurements ol'enamel thickness are less accuratc thall
Lateral thickne.ç.ç
v a l u e s o b t a i n e d l r o m t h e c r o w n o r , ' e r a l l( \ { a r t i n , 1 9 8 3 ; B e v n o n & \ \ ' o o d , 1 9 8 6 1 .E n a m e l
t h i c k n e s ss h o w s a t e n d e n c y t o i n c r c a s cw i t h t o o t h s i z c ( ( ) r i n e & \ ' I a r t i n , l 9 B B a t . U n f o r t u n a t e l y t h i s k i n d o l ' m e a s u r e m e n t c o u l d n o t l ) e c a l c u l a t e d l r o m o u r s a m p l e b c c a u s eo { -t h c
impossibility of'making tooth sectionsand the li'agmentary preservation ol'teeth.
'I'he
lateral thickness was obtained as defined bv lleynon & Wood (19861. It rvas taken at
least 1.0 mm from dentine horn and perpendicular to FlDJ in the lateral làce o{'teeth analvsed.
PARAN'I'H R O PTU'I'OO'I-H DE\TELOPML,NT
141
It u'as not possiblc to t:rke tlie anglc striae EDJ and thc course o1'striacrvererclralvti rvith
s o r r c r c s e r v a t i o n si n t $ , o t e e t h : O m o 3 3 - 3 3 2 5a n d ( ) m o 3 3 - 6 5 .T h e e n a m c l t h i c k n e s su ' t t sn o t
-I'herse
teeth present their Iractures oblicluclv liom c:uspalt.r cervix
nrcasurcclin Omo 33-3325.
ancl not perpcndiculnl to Fll).J.\'loreover, the brokcn surînt:esalc constitutec.lbv tu'rt Plane
f i ' a t ' t u l e s .H o n e v e r . t h c s e c ' h a r a r : t e r i s t i ccsl i c ln o t : r f l e c t a t t c m p l s t o o l ) t a i r l t h e n u m b e r o l
stliae anrl thc clou'n heiglit.
Results
' \ l l s t l i a c \ \ c r e n r e t i (u l o u s l r t ' o u n t e d l i o r n c a c h o v e r a l l l r r o k c r ts u r l à c e .R e s u l t sl ' o re a t : ht o o t h
-I-hc
v a r i a t i o n o l ' r r u m b c r o f ' s t l i u ei n r n o l a r s .o n e \ I 2 a n c i t h r e e \ ' 1 3 .
a r e p r e s e n t c ( li n l ' u l r l e l .
i26 striael
ci'I'. hoi.;tii.l0 stliac is llrlgcr than the vliriatit-,nobscn ccl in molars ol It. atthiopica.i
u ' h i c h i s l t ' p r c s c n t c c ll r v t u ' o \ 1 2 a n c l n l o \ 1 3 . T h c t r u n r b e t ' o l ' s t r i i i e : r n d t t r t ' t t u n t b e r o f
'l'he
v a l u e so 1 ' O m o
ccrvicalstriacslrou the surle valirtion in \I2 and in \13 ol'l'. aethiofitu:.
1 , t l - 2 f b r t h e s ec h r i l a c t e r i s t i c su l c c o n ' r p l i s e cl lr v t h e v a r i a b i l i t r ' o l ; s e n ' e c li n - \ I 3 o l ' P . b o i : e i .
Thcre is no clifièrcnce in the ratio of numirer o1'cen'icalstriae ancl tl'reratio ot-c'en-icalheight
l ) c t \ \ e c n\ 1 2 : r r r d\ [ . ] i r r t ot n r , s p e ti t - s .
Thc uinge o1'r'ari:rtionand the mean of striae of Retzir.rsof the trvo spccicsare presctrtediu
'l'able
2.
-I'hc
155 75 .
than P. bni:ti II ' a r a n t l L r r . ( taue. ;t h i o p i t : ussh o n s f e n ' e r s t r i a c i I : 1 1 6 ' 5 1
d i f l c r c n c e l r e t u , c c nt h e m e a r r so f ' t h e t w o s p e t : i e si s s i g n i l i c a n t .T h c c o n f l d e n c el i r n i t : r t 9 i t ( ' , ,
t n overlap in the mearr
t F i g u r c 1 2 r f i o r n t l i t - e i g h t t e c t l i a n a l v s e ds h o n ' st h a t u ' c c : r n e x p e r c a
v a l r r e sl r c t r l c e n t h e s cs p c c i e s .t h e r r r c a nn u m b c r o f s t r i a c [ i n ' P . a e t h i o p i r i rusi t h a t ' o t t f i c l e n c e
l i r r r i t o 1 2 2 . l . t c o u l c l r a n g e b c t u e e n 9 , t ' 3 6 1 3 f l ' 6 - 1s t r i a e , u ' h e r e a s t h z r t l o r P . b o i . t eui ' i t h a
6 ( rc o L L l cble p l a c c d b c t n c c t r l 2 f i ' 8 9 l B 2 ' 6 1 s t r i a e . H o n e v e r ' . i t i s c l e a r
c o n f i c l e r r c lci n r i t r . , 1 ' 2B
evcn u'hett
thrrt thc valiution i't.rI'. hr,i.tttconrpriscsa l:irger number of'stri:ie th:rn P. aethiolicu.t
t h c s l i n r en u r n b t - r ^ o 1 ' s t r i l rcca n b c e x p e c t e d i n s p c c i m c n so î ' t u o s p c c i e s .\ I o r e o v c r . l t l a r g c r
s a n r p l er h u n c i q h t t e e t h n r i q h t r e c l u c et h e c o n f i d e n c cl i n ' r i t sb e c a u s ct h e v a r i a t i o r t r : r n g e s1 ô r
otrr srrnrplesclo not oveliup: the number o1'striacin P. aethiapicllr':rriesfrom l0't 130:rncl in
P. bai;tit'onr 139 I 79.
Taltlc 2 lii.o shou s the c'orrelation bctrveen the number o{'striaeti{'Rctzius and the trumber
o T ' s t r i a ei n t h c c c l v i c a l s t a s c . O n l r " P . ô o l s r is h o r v sa s i s n i f i c a n t c o r r e l a t i o n t o y ' : 0 ' 0 5 . I t
i n a m o l a r i s k n o r v n t h c t o t a l n u m l ) c r o f s t r i a ec a n
i n d i c a t e st h a t i 1 ' t h cn u r n l r t - ro 1 - p e r i k v r n a t a
be clecluct-cl.-\everthclcss. the number oT'striae obtained Iiorn the numbcr of perikvmata
m l s t i ) c r l e u t e c ln i t h c a u t i o r r b e ca u s co l ' t h c d i l T i : u l n , o 1 ' a c c u r a t e l l ' c o u n t i n et h e p e r i k v m a t a .
ethiopit:utancllt.boisei.
T h e c o r r l s c o l ' s t l i u e o l ' R c t z i r - r s u ' l r s s h o r . v n t o b c d i f l ' c r e n t b e t r , r I. 'e. a
cn
the collrsc c-rl'allstriae is homogcncous: the striae are verv concavc to EI) in
ln [t. atlhiupit't1.r
kxvcr mol:rls FisLrrc B l and a littlc concavc in upper molars (I"igure I I I in the n,hole hcight
of latt:ral broken surlirce ancl. ext:cpt in most cen'ical arrd cuspal striae, thcv are'u'ert'lotrg
iFigures t]. I I ancl l3 . -\ear the cen'ix the striae shtxv a parallel course to the enarnel surface
alcl rurr through almost all the lateral face. But, in the innermost course o1'striae rvhicl'r
touches the El) in the centr:rl :ind cer.,'ir:alareas, thc course is straight or barelt'cotrvex. No
clifferenccs\\ere seenin cliflèrent lateral faccs Ior the same indir.'idual.
I t P . h o i s eti h e s t r i : i ep r e s e n td i f l è r e n t c o u r s e sa k r n g t h e s a m e { : r c c i F i s u r e 1 3 1 .T h e s t r i a ' s
crourseo1'cusp:rl :rreli tin this case it i:orresponds to cuspal stagc) is ('on(tave to EQ| but
the conca\re course ()1'striaeis not rclund but is t:ortstituted
contrarY to that o|P. aethiopicel.i,
o 1 ' t r v op r i n c i p a l d i r e c t i o n s i F i g u r e s 9 , l 0 a n d 1 3 1 .T h e s e a r e m o r e p r o n o u n c e d i n l o r v c r t h a n
+42
Table I
F. V. RAMIREZ-RO7,7.1
Tooth by tooth results
1 ) , 'h t
No.SR
pk
,,Pk
C ) m o8 4 -1 0 0
()rno 57.6-2'14
Omo 33-3325
O n r o 3 3 - 6 17 2
l3L)
t05
104
t2i
4B
3B
28
+3
"11
36
2l
3+
20 30
20 30
20 30
l0 20
C)nro33-6ir
C ) m o7 t i - 3 7
Orno141-l
Omo l4l-2
I ir5
179
139
l:r0
5r'l
9ir
.il
60
3ir
53
29
+t)
.t0
30 .t0
.r0
4tl
of cervic:rl striac;
of striae o[' Retzius: pk=numbcr
No. SR=numbcr
o,, hc: ratio ol'cervical heieht.
,, pk = ratio ofccrlical striae,
Table 2
Nurnber of striae of Retzius
I'. aethi(titut
Range
^I
S.D,
S .E , ,
CI
r: SR-pk
I 0,r 130
11 6 : r
I3.92
ri.gti
22.1+
i 9 4 . 3 61 3 8 . 6 . 1 i
It. hat.çet
1 3 9i 7 9
I 5 57 5
I6'BB
B 4't
26.86
i l 2 B . 8 9l B 2 ' 6 1
1:0 05
SR : Striac o[ Retzius; CI : colrfidence limits; r: SR-pk : correlation
bcts'cen the number of striae and number of pcrikvntata. Students /-tcst
bctween thc rlrmber ofst.;o1 :p <0'02.
upper molars. The cervical stase comprises a central and cen'ical area, both with a different
stria course. In the central area the striae run rather straight lrom liDJ to the enamel surface.
In the cervical area the course is straight in the inner hall'and a little corrvex in the outer half.
The striae o1'the cervical stase, even thosc of the ccntral area, run obliquely through the
'l-he
same kind of
enamel thickness and reach the enamel sur{àce after a short course.
yariation in the r:ourse of striac is seen in all Iàces for one individual and in all specimens
assisned tctP. boisei.
The anah'sesof different broken surfacesIbr each tooth show that the variation o1'theslope
of tl'restriae rvitli the E,DJ along the FiDJ are ah,vavssimilar in the lateral faces.'fhe striac'n'ariationalong
EDJ angle not onll' presentsdifferent r,'aluesin two spcciesbut thc Patterns of
than in P. bai.çei
the lateral facesvary. In general, the angles are more acutc in P. aethiolticu.r
join
anglc in botli
at
a
similar
EDJ
striac
the
area,
the
in
the
cervical
Nevcrtheiess,
iTable 3 ).
in
the lateral
o1'ansles
(see
variations
the
different
IIost
important
are
l6).
ligure
species
(
F
i
g
u
r
e
l
4
)
,
t
h
e
a
n
g
l
e
s
b
e
c
o
m
e
l
e
s
s
a
c
u
t
e
a
s
t
h
e
d
i
s
t
a
n
c
e
t
o
thecen'ixis
f à c e s I. n P . a e t h i o p i c u s
ancl
(Figurc
in
central:rrea
the
are
morc
obtuse
15),
anglcs
P.
the
in
boisei
smaller. \{hereas
Tlic
are:r.
in
cervical
angies
the
than
the
more
an
acute
slope
area
present
those in the cuspal
ansle mean for ear:h area shorving clearlv the diflèrent patterns in two speciesare plotted in
Fisure 16. As shorvn in Figures l4 and 15, angles change between specimens;hor,vever,the
patterr) of variation remains the same in individuals assignedto the same specics.
143
P ARANTH ROPTIS TOOTH DEVELOPME NT
190
180
170
160
1-50
?uo
z
130
120
110
r00
90
P. aethiopicus
P. boisei
l ' i g u r c 1 2 . C l c i r r f i r l t ' n c cl i n r i r s a t ! ) 5 " , , . - \ l t h o u g h a r 1 i r l r p ( ) r t a n t o v e r l a p c a r t b e e x P e . t c d i r t t l t t ' r t u m b c r o l
s t r i a r i r r t \ \ ' o s p c c i c - \ .t l r c v a r i a t i o n o l t i n t e o f c r o u l r l i r r r n a t i o r t i n P . b o i s c it e n d s t o w : r r d s g r t a t c r r a l u e s t h a t l
t h a t 1 f 1 , . n t t h i a p t t u : .s o \ v c ( a l l s p c t r k a t r o u t a l o n g e r m o l a r c r o l t t { b r n t a t i o n t i m c i n P . D o it , i .
Table 3
Angles
measurements
by specirnen,
area and mean
area
\'lean
Ciuspal
(le n tlal
C l e r v i ta l
L , u \ l ) i ll
Clcntral
( lcrr ical
()mo 8'l-100 O m o 5 7 . ( i - 2 ' l ' 1 ( ) r n o 3 3 - 6I 7 2
.9
l
5
15
lb
It)
'2'2
l9
3')
( ) m o l - ll - 2
C ) r n oI ' 1 1 - l
Omo 7ti-37
'22
'25
l0
3li
2u
3{:}
2+
l3
3l
1
l+
2+
19
3'2
23
'fhe
lpmber o1-striaeincluded in the cervical stage ancl the pcrcentagc cornpriscclb1' them
'l'he
tren'icalstaqe in
a s * e l l a s r h e f a r i o o 1 ' c c n i r : a l s t a g e h e i g h t a r e s i ' u ' e ni n T a b l e 4 .
't
if
I 95], thc setrottd
in
P.
boi.çe
4ft,r
than
striae
l'. aelltittpitutconrprist'sa smallcr number of
i2B
o
1
'
s
t
r
i
a tits s m a l l e r i n P .
n
u
m
b
t
:
r
t
o
t
n
l
H
o
u
'
e
v
e
r
,
a
s
t
h
e
nith a lulgcl runge th:rn the Ibrn'rer.
almost
striac
disappczrrs
number
of
cenu'ic:il
in
thc
the intpoftant dillèrencc, seen
aethigpitu.t
c
o
m
p
letell.
o
v
c
r
l
a
p
:
r
l
m
o
s
t
t
h
c
c
l
i
s
t
r
i
b
u
t
i
o
n
s
ç o m p l c t e l v n h e n t h t ' p c l c e n t a g e sa r e c o m p : r r e d :
aelhiopicu.r
Paranthropu.t
rtf
vari:rtion.
range
Brrt tlre cliflèr'errcclemaitis in the rnean:rnd irt the
shgrvslou' r'uluesu'ith a r:inge bcnveerr 26'9 36'9",, lvhile P. ôollri presentsliigh value s u'ith a
ra1gcreachinq50",,29.l ir3.1",,).Tl'reheightcon'rprisedltvten'icalstriacinfivospeciesis
yerr.dissinrilar. flen'ical stagc in lt. aelhir.,picus
takes ltenvercn15 30",, n'hercas in P bai.çeiit
i n c l u d e s4 0 , ' , , .O n t h c ' c n a m e l s u r h c e p c r i k v m a t a a r e l o c a t c d o v e r : r l l l a t e r a l I ' : r c efsi ' o m n e a r
pcrikl'rnata:rre placed do'"vn,iar
rvhercasn P. aelhiopia.r.i
tlre ccrr.ix ro occlusal linc in P. Doisei,
Ii-orn the occlusal lirre and a distant:e separatesthe last liom tlie t:en'ix.
'l-hest'results
rcf'lectttrat the r:tintribution u{'the cervical stagc for crorvn lirrmation di{Iers
than in P. hoi.çtti.
lbllorr,ing tlre specicsis much lessimportantin P. aethirtplca.r
1 1 1
t11
F. V. RAMIREZ-ROZZI
}igurel:]'l,t'1i:rrrcsi:l]liltttttI.ecliagranrtl1.()mo3lJ.tjl O o i
i t l n t ( ) s 1l t l l t h c l i c c h e i e l r t l i t h a r c r v c o n c l l v e c o u r s t u h i t l r i , . h o r r r o g t n c o u s l i r r m c l e t t t i r t el t t t t t r 1 o t e L r i r .
\t'artIttccrlirtlrr'striecstillnlltitttaitta1larallcl('()Llfs('1()stlI.i:|((
r l r t c r r r p i r l s t r r q t i n c r o r r ' n l i i r r r r a t i o u . R i g h t : n r e s i a l l i - r r c t L r l cc l i r r g r a n r o f O I n o 7 6 - 3 7 : l t . b t t i ' t t . l l t e s t r i a t
r r i . r i.r r r l r c c L r s p a sl t a g i . I n t h e c c r r i c l r l s t l r g ct l r t s h o r t s t r i a t ' a r ( s l r r i g h t o r s t r a i q l t l i r t t h e i t t l t t r h a l l e n c l
c o r r rc r i n t l r e r i r r t c rI r a l l .
Table 4
Cervical and cuspal stages relationship
\pttrts
Nunrbcr
ol yrk
28 +u
+l 95
i, Irk
26.9 36.9
1 9 . 55 3 . 1
' ( lrou.n
,,
cerr ical stagt ht ight
lir 30
.r0
T l r c l a t e l r r l t l r i t k n c s so 1 - e n a m c il s p r c s c n t c c il n ' l ' a b l t ' i t . P a r a n t h r o p uôça i . ç es ih t t n ' sa t h i c k e l
t'narncl rvitir u lurrqc bctu een 2200 25100pnr rr,herelrstltc ratrge oI'P. uethiofinl.iertcnds liortt
l610 l9l0 ;.trn.
Molar teeth development in P. aethiopicus and P. boisei
s f ' c t t : r m e lg r o u ' t h - m : r r k e r sc t r : r b l e su s t r r
. \ s i n c l i c a t c di r r f i g L u ' e 6 . t h c s t u c l vo l ' s o n r c : r s p e c t o
'l'al;lle(i
sttnrnritrizcs
i c l e n t i l \ ' a n c l c l e l i n e s e v c r : r l c h a r a c t e r i s t i c so 1 ' t o o t h d e v e l o p m c r t .
t l r c t o o t h d e v e l o p n i e t r tt r s p e c t si n l è r a l t l c i n t w , o s p e c i c sl i ' o m o u r r c s L r l t sa u d r c v e a l s s o t r t c
d i f l è r e n t ' e si r r t h c i l m o l a r t c c t h d c v c l o p n ' r e n t h u t a l l o u ' e a c : hs p c c i c st o b e t ' l l t l a c t e l i z e d .
lirrrns in :r shorter timt--tltatt rn [t. hoi-rei..\serpccted liorrt
Tlrc rnol:rr crou'rr ol'P. aethiopicus
t l r c n u n r L r e r o l - s t r i aP
c . a e t h i o p i c ur .ni o l a r s t i i k c b e t r v c e nl ' 9 9 2 ' 4 9 v e a r s u ' i t h a û l c a n o 1 - 2 ' 2 3
PA R A NTH Ro PrI'I'Oo'I'H
+45
DEVIiI,OPMEN'I'
35
30
25
lzo
(^
o
t <
s - -
l0
5
l,
Central
Cuspal
Cervical
Area
I i q r r r l I l . . \ n g l c n r ( a s u r e r r r c l l t sb c l l c c r r s t r i a c a r t d l , L ) f i I r t e e r h o l ' l ' . a t l h i o l i t u . t . I h c a r r g - l c sl r t ' c a t n t ' l c s s
.lrLLtt'lt'1hct]]islltttlt'lrlt.ctrilissnlirllt'r..SI{-striaerr1RctziLrs;},I|-tIramclclt'rrtirrt'.jLrnctirlt oo l
O r r r o : r 7 . { i - 2 J ' l i; . " ( ) n r o l l i l - ( i l 7 2 .
l J - t i-0 l ) :
Table
5
Lateral
thickness
ofenamel
L r t t , - r . r lt l r i , k r l s s p t t t
)l)('( lnr( rls
l9lt)
I (;.)()
I 6U0
25(X)
2i0()
2250
2300
O r r r ot ] - l 1 0 0
O r n o. r 7 . ( l - 2 1 l
O r n o - i l J - I{7r 2
( ) r r r ol l l l - ( r r
( ) r r r o7 ( r - l l 7
( ) n r rl { l - l
( ) r n ol { l - 2
( ) n r r , : J : l - l l l l I I t a s t ' r c l u c l e c l l r t c a L r s c i 1 s f i a c t r rpr tl a n c s o b l i t 1 r r t o t i D I g i r r
. r n r i ' l t r t i l i n g t r t a r t r t ' lt h i t k t t c s s .
Table
6
Characteristics
oftooth
development
in east Lfriczr
Paranthropus
species
l'. utllùoltr ut
I i n r e l i r r r r r a t i o r rr t ' a r s
furret' rrrilrrt l
f)illi rcrrtiirtion rate'
\rurrbcr ol stctr'1ot
l L n r t ' lr b l l r s t .
(l n ical sLast
No. SR
",, IL'ight
lrtio ol
r c r r i c a l s t i r g ci r r c r o u I r
1 . 1 )21.)+ 9
2.23
rvl-rl-i
It. bot:t t
: 67 3.13
?.1)9
l-a-l'
r c rr l r i q h
lriql
lon
high
l otr
hiqh
+16
F. V. RAMIREZ-RO7,7,I
35
3f)
r!
(t
1-5
t0
Cuspal
Central
Cervical
Area
l f i g u r c I : 1 .. \ n g l t r n t . a s u r e r r l e n t sl ) e t u c e n s t r i a t a r r c ll i D J i n t e t t h o l 'P . b a i t t t . \ l o r e o b t u s c a l r g l e sa r c p l a c e d
irrthccerrtralareauhilethoscintlicruspalandcerricalareasllrca(ute.lhetnostrtcutellreseeninthc
Omo l4t-2;
'
cuspal area. SR-striae ol Retzius: EIf -s11'tr..1 dcrttitre-junctioti. f (Jrno l6-3j:
I
Onro l{l-1.
FJ
I
d
< r l
10
Cuspal
Central
Cervical
Area
}ietrrel(j,'\It'arratrgleslrt'trrt'ctlstriaelrfRt'tziusaIrcl}ll|ilrthc]atcral1irtcateas.
. .ltous nr()r( A.utc lurglt s in the cuspal and ( ( rttral ltrcas tltatt lt. boisci N . l)ifli'rt Irt Jlatlcrlrsilr the
t l r r i a { i o r r o l e n g l c - l. i o r r r t h e d c n t i n e l r o r n t o ( e r v i x r t r t l i r u r t d i t r t u o s l t c t i e s s t c ( e \ l . S R - s l r i a ( ( ) l R e t z i u s :
I I lJ
, t r . t t t tl , , l t r r t i t t ,i u r r (l i , ' t r .
\ ears 1.92 2'87 \'clrs i to firrm tlieir cro\\,n) rvliilc P. ûoi.çr'lmolar cr'()\\'rlsare lirrn'red irr
2 ' 6 7 3 ' ' t 3 r ' e a r su i t l t a m e a n o l ' 2 ' 9 9 r e a r s i 2 ' 5 6 - 3 ' [ ] ' l v c a r s l .
'flre
speciescarl be exPlained
clil]èrencesin time o1'crou,nlirrnration bclu'een Paranthropus
firr thc lengtli of srriae and the cliflèrcntiation rate cstimated lrom the rlngle l)et\\'eenstriac
ancl EDJ.'l'hc slopeof'striaervith thc F)DJ iTable 3, Figure 14, indicatesthat the diflcre n r i a t i o r )r a t e i n P . a e t h i o p i r ua. sp p e a r s t o b e v c r v l à s t i n t h e ( ' u s p a l : i r e a i n t c a n a t t g l c : 7 " i
ancl recluces as cro\\,n firrrnation ne:rrs completiorr rvith a Ïàst rate irt thc cen'ic:rl area
P A R A N T H R O P L I ST O O T H D E V E I , O P M E N T
4+7
ôoi.ieishows a Iàst diflèrentiation ratc in the cuspal (mean
imearr ansle:24'") . Paranthropus
areas. rvhereasthe central area presents
ancl cen'ical imcan anglc:23')
algle:19'i
(rnean
The faster differentiation rate in
ansle:32")
rate
diflèrcntiatic,n
a1 aycrage
lormer
a large number o{'ameloblastswere
in
tlic
that
indicates
irr
P.
hoisei
P. aelhiopirusthan
'l'his
is confirmecl bv the course
period.
a
short
front
over
matrix
inclucled in the enantel
i
n
[
'
.
a
e
l
h
i o p i c al sF i g u r e l 3 ) , m a k i n e
l
o
n
g
e
r
a
n
d
c
o
n
c
a
v
e
s
t
r
i
a
e
.
'
l
'
h
e
r
,
a
r
e
a r - r dl e r r s t l ro 1 - t h c
n
u
m
b
e r o l - a m e l o b l a s t sa c t i v e a t
a
f
r
o
n
t
i
n
c
l
u
d
c
d
s
r
e
a
t
e
r
m
a
t
l
i
x
f
o
r
m
i
n
g
clear thut a larger
i
n
t
h
c c e n t r a l : r r e a p r t t d u c e so r
r
a
t
c
f
o
u
n
d
l
o
r
v
e
r
d
i
f
l
è
r
e
n
t
i
a
t
i
o
l
l
I
1
I
t
.
b
o
i
s
e
i
t
h
c
Ir1\'o1c tirre.
the straight stliae lr,hich crovera shorl distance bcltrre tliet reach the cn:rmel
l1cc<;lnrpanies
'
l
'
i
g
u
r
e 1 3r . ] ' h e h i g h e r d i l l e r e n t i a t i o n r a t e u n d t h e g r e a t e r n u m b e r o l ' a m e l o b l a s t s
surlàcc
than irl
a(.ti\.eat 2urv one timc explain the shorter time for crro\,vlllitrmation in P. acthiopicu.r
[' . bai.çti.
It P. æthiopi.a.r.the longer striae rvhich co\.cr:rlmost all of the lateral 1àccmaintain everr
thccentralareainthcsameformoffinaloutlineofcrown(FiguresBandIIr'lnP hoiseithe
stri:rc clo not represeltt the final outline of the crown, not even the last striac of cuspal stage
Figure 9 .'fhis dillèrence in the ftrrm of the striae, u,'ebclieve, is caused bv the dissimilar
and P. boisei'scervical stage formation in crorvn
relative importance of the P. aethiopicus'
lirlnration.
The irnportant difference in the cervical stage development is reflected in the cervical
Seishrs 9f molars o1'the trvo species.In relative cro$'n heisht the cuspal stage is alwavs the
prosrimportant e\:enr,r,henit includes 50u'; oI'striae.The ratio of cervical stage height was the
specimens (40t'o); it was not influenced by the percentage o1'striae
sanre in all P. boi.çei
inclucleclin the ccrr,,icalstage.The percentage of striae comprised by the cervical stage can be
rhe sanre in P. aethiopiczrand in P. boi.çei(Table 4t. Nevertheless,the ratio o1'cervical stage
Unlike P. boisei,the
heislrt fcnrails cliffercnr; it increaseslrom l5 to 30oo in P. aethiopirr.ç.
r.elltir.e height oT-thecervical stage might be influenced bv the percentage o1'striaeincrluded
in it in P. atthioficu.;.
yt P. acthirtltitrz.i
a large proportion of'the timc of cror."'nforrnation takes place principallv in
l . n r p u l s t a q e .T h e c c n ' i c a l s t a g ei n c l u d e sf e l v c r s t r i a ca n d c o r n p r i s c so n l v u p t o 3 6 ' 9 " , , i - l ' a b l c
{ , Itr 1r.ô,,tit,i tfic celr'icirl stasc could be considered in time lbrrr-rationas importatrt as cuspal
can reach53'1",,of the total number iTable'll.;\ short time
s t a g e :t [ e l l r n r ] r e r o 1 - s t r i a e
thus thc ameloseplr'iite: thc encl ol-activitv ol'tlic first and l:rst ameloblasts in P. aethiopictt.t'
the first ameloblastsrnight finish their activit)' some
lrlrrrt. relcl tc.ru ork as a u hole . ln P. boi.rei,
rinre lteliire the lasr anrcl,tblastsbecrimc active; the high values lor thc cen'ical stage indicate
that tht' anrcloblastsoperatc itr suct:essiveÉIrouPs.
can be ciraracterized:rsa development
Tlrerclirle rlolar tooth clevelopment in P. aethiolticl.ç
t h a r l o r n t s t h e c r o u n i n a s h o r t t i m e l ; v i n c l u d i n g a l a r g c n u m b e r o f a m e l o b l a s t sa c t i v e a t a n \ '
q i ç e n t i 1 r e . T h e o v c r a l l n u m b e r o l ' a m e l o b l a s l si n v o l r " e di n c r o r v n l o r m a t i o r l o p e r a t e sa s a
l l r o l e . T l i c r l a t r i r - l o r m i n g f r o n t r e m a i n s l a r g e b e c a u s ca l a s t d i f f e r e n t i a t i o n r a t c i s m a i n tailecl clLrling all the tirne o{'crolr,n ftrrmation producing a widcspread cuspal stage that
arrir.esclonn near the cen'ir. The cen,it:al stage t:rimprisesthe last period zrnd is limited to a
shorvs a longer tnolar crou'n developmer-rt
Doi.çel
recluc.cclrrrea near the cervix. Paranthropus
lith a large rnatrix-lbrming lront a large number of ameloblasts active at anv one time
restricted to cuspai stagc. A lower diffcrentiation ratc in thc central arca produces the
fiegi1ni1g of the cen'ical stage near t]re middlc crou'n height, srimetimes comprising 50':',,
of the tot:rl tin're o1' cror,vn formation so that the ameloblasts are active in successi'u'e
groups.
448
F. \I. RAMIREZ-ROZ,7.'I
Discussion
f.lomparison ol'thc rcsults firr \I2 and \I3 in c:ich speciesshorvsus th:rt crou'rr lbrmation tirne
lr'oulcl be similar fbr cliflerent kirrclol'nrolals. In great aLXrs,timc of'crou'n lirrmation itrcreases
a l i t t l e l i c r n r l i r s t m o l u r s t o t h i f aml o l : i l r , \ n t ' m o n e r l a 1 . .1 9 9l : B e v r r o r t t L a L . , l 9 9rI. T h c t i r n c o l
crou,n lirrmatiorr incre:rsesalso bct'"r,ccnthc first :rnd ser:onclnrolar in modertt httmatrs lrut,
a l t h o r - r g ht h e m c a n v a l u e s l r r e c l u i t c c l i f i ' c r c r l l .i t s \ i r r i i r t i , ' n t e u u r i n s s i m i l l r r b e t n e e t r t h e
s e t ' o n cal n d t h c t h i r d m o l a l u ' i t h a r a n g e i n l r o t h o 1 ' t h t - r no 1 ' 2 ' 2 3 4 i \ [ o o r r c c s s e 1a 1 . ,1 ! ] 6 3 r .
'l'hrrs
urc rlot inlluerrceclbv r-rsing
tlrc clillèrencesoLrscrveclbetireen It. at/hiolitu.tancl P. htti,çei
difTèrcnt rnolars firr analtsis and sin'rilarr:halactcristicsbetwecn \12 ancl Il3 in nvo sltccieso1
althorrqh thc sn'ralls:rmple preclurles attr cotrt'litsion.it rniqht inclit'atc that it is
ItrtrarLlhropus,
the same fèlrturc ia parallelisrni'r obscn ccl itr tltoclet'ttIttttt'tlttts.
s ' u ss i m i l a t ' t o t h a t
\ I a n n ( 1 9 7 5 l h a s d e c l u r : c dt h : r t t h c t i n r c f i r r n ' r a t i o ni n . \ u s t r a l o p i t h e t ' i n t ' u
o l l n o d e r n h u r n i r n sf b r t h e r e l u t i v cs c c l u c n t i a l s t a g ci sn : r l lt eet h . L a t e r r l o r k s l t a v ec l e m o n s t r l r t e c l
tliat the sequence of'teeth rler.eloprnent in .lu.rlraloltilherutafiicanu.ris more ape-like than
l i u n r a r r - l i k e: r r r c lt h a t r h e l e i s p a r a l l e l i s r ni n l h t ' l 1 \ l l s e q t r c r x ' ei n [ ' a r a n l h r o p u as n d H o m a
i D e a n . l ! 1 8 5 . l 9 U 7 a . ô ;S n r i t h . 1 9 8 6 , l 9 U 9 \ o c l a t a h a s b e e n s u g g c s t c c l - o r^ ' l u , ; l r a l o p i t h e c u . t
r.,bselvt'cl
Iit.,mlossiIhonritricls:trc incltrclcclitr moclcrtrh urn:rn
afàren.si
s. H orr er t'r'.th c scclrrt'nces
v a r i a t i o r rL \ l a n n . 1 9 8 8 :\ I u r r r r e l u l . . l 9 B t - . 1 1 ' n e : i s s u r r t c . t c l ' o \ \ n f i r r m a t i toi rmr e f i r r t n o c l c r r t
hurnan nrol:rrs of 2'5 r'c:rrs Dean & \\'oocl, l9[Jl . oLrl results sltou it lotiger tirnc ol'crolvtr
lirrmaticrrrn P . hrti.;titharr in t he rnodern Horno.lt Iirct a large variatit.rttitt crot tr litrmation
time nrust Lreexpet'teclin modern humans if clata fiorn a l:rrge number o1'*'orks is cortsidcrcd
i L o s a n & K r o n l è l d . 1 9 3 3 : S c h o u r & \ ' [ a s s l c r , 1 9 4 0 :K r o n l è l d . 1 9 5 ' t :G l e i s e r & H u n t . 1 ! ] 5 5 ;
G : r r n e / a 1 .1, 9 5 9 ;F a n n i n s , 1 9 6l : \ o l l a , 1 9 6 0 ;\ I o o r r e e s s r l a 1 .1. 9 6 3 ; F a s s1. 9 6 9 :D c m i r j i a n &
L e v e s q u e , 1 9 7 9 ;S h e l l i s ,l 9 B , t ) a l t h o u g h S m i t h . 1 9 t t 7 . l 9 8 9 p r o p o s e dt h : r t \ l o o r r e e s s r / a 1 . ' s
u,ork is the last and mc,rstcomplete of raclioerapliic stLrcliesusinq apprepriate statistical
p r o c e d u r e s ( s e e S r n i t h , 1 9 91 1 . \ ' I o o r r e e s sr / a / . ; 1 9 6 3 e s t i m a t e a m e a n o 1 ' 2 ' 1 . 2 f l a n c l
2'75 vears fcrrN'Il, NI2 and \'{3 o1'modcrn humatrs.
Our resultsdcmonstrate that variations in crou n frrrnratiotrtin'reoverlap in lw'ctParanthropus
'l'he
clifference betrveen
speciesand inclecclthis rnust be expectecl fbr :rll hon'rinicl spccies.
boi.rtiprcscnts a
slreciescalr be seen irr thc rclative tendencies ol'the valiations. Paranlhropu.s
variation ti:nding tou.arclsa longer c'rorvn firrmation tirne th:rn the P. aethiopicu.t'r'ariation
u liich tcnds tou ards shorter periods.
Prcvious uorks on time olt:rorvn formation have suggestcd that l'. ôoi.çriI'ormecl their
"irr
nrolars
t l i t - s a m e ,o f l e s s .t i n r c t h a n m o c l e r nh u m a r r s " i l J c v t r o n& \ \ ' r i u c l . 1 9 8 7 : 4 9 6 t . ' l ' h c s c
a u t h o r s p r o p o s e a t i m er 2 r n g e o l ' m o l a r c r o u ' n f c r r r n a t i o n o f 2 ' 122' 5 9 \ ' e a r s i n ^ / ' . â o i . i a t . w h i l e
thev h:rve suegesteclthat modern humans complett--molar crorvn grorvth in approxin-ratelv
2 . 5 5 r ' e a r s .B c l ' n o n & \ V o o d p r o p o s c d t h a t t h c s h r t r t e rt i m c l b r m a t i o : n i n P . b o i s e i u ' adsu c t o : r
1àstcr cliflèrentiation rate ancl a f:rster enamel sccretion irr spite of its tliicker ctrlimel :rncl
larger molars. Holvever, the variation o1'crorvn lormation time in modern human nrolars
i l l o o r r e e s s e t a l . , 1 9 6 3 l t : o r n p r i s e st h e d a t a p l o p o s e d l l l . B c r , n o n & \ \ - o o c i i l 9 8 7 . \ l o r e o v e r .
our resultsarc llot in :rgreement n'ith a shortcr time o1'crou'rtmol:rr frrrrnation in P. ôotselthan
Thc resr.rlts
in moclcrn I Ionto,ctrtthe contrar\, the r.'propose a longcr tirnc Iirrnration irt P. Dat.çri.
estimatcd in Ornti sarnplc, 2.67 3.+'3r'ears,do not overl.lp the rattge ploposecl br Bevnou &
\\'oocl, though it lvould be expet:teclto be incluclccl in the speciesr':rriatit.rtr:rs suegestedbv
confidence limits i Fisure 121.Nevt-rthclcsssome methoclologit'al proceclurcscan explain the
diflèrence.
PARANT'HROPT,TS TOOTH
+49
DE,VIiI,OPNIENl'
Mesial
face
a
b
c
Last striae
of Retzius
d
1l)r'cs. lheptrikrntata a. lt.c.....h rurtoblicluclv
I : i g i r r c l T . l ) i l l i ' r c r r c t i n t h en u n r l r c r o l\ t r i i t ( f ) ( t \ \ ' ( n
op rlrt lingual lrrrrllrrrcral làces.prrducint thc last orrcs 1.g, h are ortlr represettltxliIr the distal hall ril'
l ( ) () t i l . ( l ( ) l r 1 t 1 1 ' g r r 1 r ' t l rl i n c s m a c l t o r r l r o t t n r c s i a l f i t c t ' t a t t r r c q l e c t t l t t ' t r l t r i r a l t ' t t t t o 0 B B r c a r i .
l l e r n o n & \ \ ' o o d i I 9 t t 6 . I g B 7 . rn o r k c d u i t h r o l r u s ts p c c i m c n sI i o m K o o l r i F o r a . K e n r . a a n d
( ) l c l L r r a i ( i o r g e . T a n z a n i a , a l l a t t r i b u t e c l t o P . b o i . r e iI.t i s p o s s i b l e t h : r t t l i c s e s p c c i m e n s
Bcr,notr & \{ood ( l9B7i did
irrclLrclcmore than one specics.the secortdonc being P. aethiopitu.t.
1ot r-stirnatethc clorvn firrnration tirnc liorn clirect obscn'alion ol) itrcremetttal grorvth lines.
.\lthr-rughthev olrt:rincclresultsirr :rgreement lvith tltose proposcd bv other ntcttuslirr n"rodern
rerm:rinu'licn indirect wavs arc ermplovcd.Holvevcr. rvc think that the nlain
hunrans. ckrr.rbts
rcrr\on lirr the clillcrcncc is to fbund the location ort plane liactures. Bet'rtoti & \\'ood 119t371
that broken surlàces\\'ere llear the dentine liorn, so thev include the first enamel
errrltirasizecl
lre
ftrlnrcd. But thesc authors rx'erlooked tl-re1:itt tlrat the broke n surlàt:esalso comprise the
to
lu.t cnamel to l;lclirlrned. The perikvmata rurl obliquely on buccal and lingual lirccs,the liist
trtrt'lrrrikrrnatrr locatcd on the distal half-suggcst th:rt molar cror,r'nformation in [t. hoisei
'
\
l
l
s
t
r
i
a
c.rl
1
7
i
.
r
n
c
s
i
:
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'l
( ) n r o 7 6 - 3 7 . h e r r u u r b c l o l ' r ' u s p a sl t r i a er v a st h e s a m c i n b o t l i r n e s i : r al n d d i s t a l f a t : e s8, 5 a n d
B - l l e s p c ' r ' r i v e l r s' .u q g e s r i n q( ( , n r i n u o u s s t r i a r c l u r i n g t h e c u s p a l s t a g e a l i d t h a t t l t c e n t i r e
. hc numlrer of'cervical
c u s p a ls l a g eu a s l b l m e c l a s : i s i n g l eu n i t i ( l r i n c & \ ' l a r t i n . l 9 B B l r 1T
the
distal
edge shou's95, rvhich
srliat' n lis vcrv diflèr'ent. tlic mesial edge prcscnts.lg n'hcrc:rs
mesial
and
distal luces. lf the
rneirns11rlillèrencc ol'0.UUvears in time frrrmation Lrctrveenthc
"crolr'tr" lormatiotr
the
neglected,
rrresiallucc 1ôrm:ition time is ret:rined and the last striac
tinre ol'Orno 76-37 u'oLrlc.lbe 2.57 r'cars, sin-rilar to rcsults proposcd bv Bevnorr & \\rood
1 9 8 7 . ' l ' h u s , s p e c i a la t t c n t i o n m u s t l ) c g i v c n t o : r n a l r , s ct h c l o c a t i o n o 1 - t h ep l a n c l i : r t : t u r e s
ancl thc course of' thc perikr,lnat:r s.J as not to ncglect somc important l)eriocl o1'crown
lirln'ration tinte .
B e v n o n & D e a r r i l 9 B 7 ) h a v c s u g g e s t e da t i m e o f - ( : r o l t ' n l o r m a t i o n o 1 ' a p p r o x i r n a t e h '
2 . . 1v e r r l sl c r ra p r e m o l a r t o o t h a t t r i b u t c d t o P . b o i . ç esi .o t h i s i s s h o r t c r t h a r r t h e p r e m o l i t r t i m e
this result cannot bc used as an arguof c'roun Ibrrnation o{'modern humans. ),{evertherlcss,
nrclrl to support :r shorter molar r:rolr,n {brm:rtion timc, because onlv otte premolar u'as
lunalvsedanci the result could ha'u'ebeen undcrestimated b1' methodological problems as the
a u r h o r s s r r g e e s t e di l 9 B 7 : t - 7 5 ' 1 F
. u r t h c r m o r e J a n e \ \ ' s t u d , vo 1 ' t i m c o 1 ' t : r o r v t ft i r r m : r t i o n e s t i nrrrresirr prcmolars suggestsa longcr pcriod o1'3r'ears iRamirez-Rrtzzi.h prcp.l. ()theru'ise
,t50
F. V. RAMIREZ.t{O7,7.I
this r:onfirms Bet'non & Dean's suggestion that the premolars became molarizecl in ltoth
exterrral morpholoev and time o1'tror'r'rtlirlrnlrtion in P. boi.tei.
The carlv der,ekrpmcnt of incisivesancl a cliflèr'cntcro\\'n Ii,rrmation time in P. hoiseithan irt
mrrrlcrn |Iono i'De',r1,1985:Brgmagt: & Dcan. l9B5: (lonror,, I gB8: this studr.i c:rtrbe poirttercl
o u t . n o t a g e l r c r a l d i l l e r e n t p c r i o c l o [ ' d c n t a l c l e v e l o p r n c n t . ' rps r o p o s e c lb v B e v n r t t r& l ) c a n
i l 9 U 7 t b u t a d i f f e r c n c e i n s i z e a n c l u c l i r c c t 1 ù n c t i o n u lr c s l ) ( ) n s et o l o t : l L la r t a t o r n i ( t l t a t t g c s
i S i n r p s c r ne t a l . . 1 9 9 0i .
'l'lre
l o n g c r c r o w n l i , r m i r t i , r n t i n r l s r r g g c r t e di n t h i s p a p e r f b r P . b r t i . ç et hi a t r i r t t n o c l e r u
humans docs not c'ontraclict:r {iistt'r'clilièrentilrtion ratt'irr thc lbrmcr i.st'eBevnotr & \\'ood.
1 9 8 7 1G r i n c & \ { a r t i n . l S B B 1 ; i .B e r n o n & \ \ ' o o c l i 1 9 8 6 h : r v c s u g g c s t e da n a c u t e a n s l e
30 irrrobusthominicls{ionr
l t e t ' , r ' c e n s t r i a e o { ' R c t z i u s a r r d E DX.:J2 3 ' u i t h a r a n g c r . , l ' 1 t }
E a s t À f i i c a . ' l ' h e a n g l c s t h u t u ' e r e t u k r r r o r r t h e o c c l u s u l o r l e - t h i r d o f l a t e f l l l l à t : e st : a r t b c
r : o r r e l i i t c dt o o u r c u s ; r a ll i r e a . ' f h e u n g l e sc s t i n t : r t e ci ln t h i s u ' o r k l r . r rI ' . h o i , t e i : r rccl u i t e s i n t i l a r
i ' l ' a b l c 3 . F i g u r e l 5 r . n h e r e a s t h o s e n r e l r s u r c di n P . a e t h i o l t i t uu: r e n r o r e i i c u t c a u d r e t ' e a l a
en:rmel irt
laster cliflèrcntiation r:rtc than I'. boitei.\\'e lrelievc that the prescnccr.rl-hr'yrer'-thick
I t . h o i , ç ei ,i \ l a r t i n . 1 9 u 3 . 1 9 8 5 1G r i n e & \ I a r t i n . l 9 t 3 f i û e x p ; l a i n st h e l r . , t t q e rt i m e o f c r o n ' t t
l o r r n a t i o n . e r - e ni f i t s h o u s a m o r e r a p i c l c l i l l è r e n t i a t i o r )r â l e a n c l a l i i s t e r s c ( ' f e t i o r r) : i t c t h : r n
l l r u n d i n m o c l e r nh u m a n s i l l e v r t o r t& \ \ ' o o c l . 1 9 8 7r .
T l r e t i m c o f c r o u ' n l i r r m a t i r . r n : i n c lt h e n r e t h a n i s m s o 1 ' t o o t h c l c v e l o p m e n t i : n , 1 . a J à r e n . r i . r
i r r c u n p u b l i s h c c la t t l i c n ' r o r n e n t R a m i r c z - R o z z i . i n p r c p . 1 . ' l ' h e e n a n r c l l i r r n r a t i o n P a t t e r n
d e s c r i b c c li t I ' . b o i s e ui a s t : r k e n a s l r r e t e n t i o n o 1 ' t h e g r o \ \ ' t l i p a t t e r n r i l ' c l e c i c l u o u tse e t h i r t
'l'lie
1 : r st o o t h l i ) r m a t i o n
p e r m a n c n t t e e t h ' B e v n o n & \ \ ' o r . r c l1. 9 8 7 ;G r i r r c & \ I a r t i n . l 9 B B , .
u o u l d i n d i c n t e i i p a l t i c u l a r r e s p o n s cb v l o b r r s t l i n e a g c t o s e l e c t i c - rpt lt ' c s s u r ea s B c v t r o n &
".
\ \ ' o o d l 9 8 7 : , t 9 5 , h a v c s u g g e s t e d : . . t h e r e u ' a s s t r o n g s e l c c t i . r nt o 1 i ) r m t c c t h c 1 r - r i c k .l r.' . "
-l'hus
these authors propose that thc anccstral conclition *us cliaractcrized bv a slorver
c l i f l e r e n t i a t i o nr a t e a n d a s m a l l e r s e c r e t i o nr a t e . E x c e p t l r r r \ \ - a l k c r & L e a k e r ' , 1 9 8 8t , t h e r e i s
s I ' o p i n i o r rt h : r t P . a e l h i o p i c u\ \s, a st h e a n c c s t o ro f P . b o i s eri s e eG r i n e , l 9 8 B ) .
a g e n e r a lc o n s e n s u o
Therel'ore the Bet'non & \\'ood's suggesti.rnmust be rejectec.lbecause[t. aethiopicu.r
Presents:i
P.
shorvs a
Hotvel'er,
aelhiopicus
is
1àstcr
in
P.
boisei.
lormation
that
than
of
enamcl
pattern
modern
-É1orno.
in
and
that
prcscnt
earlv
formation,
dissin-rilar
to
pathr.r,al'of'tooth
particular
Earlt Homo and P. hoi.ttipatterns oferramel forrnation iire rnore similar than the P. aethiopicu.r
partern (Ramirez-Rrnzt,irt prep.l. Thus, althoush tlle cletermination cif trends in hominid
cannot be placed as thc
tooth devclopment is overbolcl, the possibilitv that P. aethiopicus
anccslor of [t. boiseimust not Lreruled out.
A f à s t c r d i l l e r e n t i a t i o n r a t e w i t h a g r e a t n u m b c r o f a m e l o b l a s t s: r c t i v e i r t a n ) g i v e l t t i m c
c l r a r a c t e r i z e dP a r a n t h r o p ucsl a d e a c c o r d i n g t o G r i n e r & \ I a r t i n ( l 9 B 8 r ) . O u r r e s u l t s l i o m
P. aethiopicu.r
confirm this observation and provide more information about its specific
aethiopicus
does not have a hyper-thick enamel as the othcr Paranthropus
status. Paranthropu.r
s p e c i e s .B u t o u r m e a s u r e m e n t o f e n a m e l t h i c k n e s si s l i n e a r a n d d o c s n o t t a k e i n t o a c c o u n t
t h e v a r i a t i o n s p r o d u c c d b y d i f f e r e n t t o o t h s i z e. N e v e r t h e l e s s ,i t i s p o s s i b l e t h a t a g r c a t
n u m b e r o f a r n e l o b l a s t sa r : t i v e a t o l l e t i m e r r o u l d n o t a l $ ' a ) ' sb e a c c o m p a t r i e d b v a h y ' p e r t h i c k e n a m e l a s p r e d i c t e d b y G r i n e & } , l a r t i n ( 1 9 8 8 a ) .T h e h y p e r - t h i c k en a m e l u o u l d n o t
perlraps cronstitute a synapomorphy shared by Paranthroptt.ispecies. A 1àster diflèrent i a t i o n r a t c c a n b e m a i n t a i n e d a s a s y n a p o m o r p h , vo n l v i f ' a t r e r r d t o f o r m t e e t h q u i c k l y
is retaincd with the rcsultins cont:lusion that P. aethiopicusrvould be rnore specialized
than P. hoiseiand must not be seen as its ancestor but as a dead brattch inthe ParanthroBu.r
clade.
I'A R A NTH R OI'T,IS'I'OOTH DE\TE,LOPMENT
,t5I
Summary
l r r o k t : ns u r { a c e so l ' t c e t h e n a } r l et h e r , r , o r k etro c h i i r a c t e r i z t :t l t e g t ' o n t l t n t a r k e r si t t
rhe t'n:rmel. cletcl'lttine sonrc diflèrences uncl clc{ine dissirnil:rr pathn'avs itt ntol:rr teetli
rlcvclolrnrerrt in hominic[ sltet'ies.Paranthropusaeihiopitu.t,u'herc ther amelol;llastsleacl thc
c l r r n r r l o r r t r : r t i o no l t c r a t i n g u s a u h o l c , s h o n s u s l t o r t c r t i r n c I b r m n t i o l t t l i a t r I ' . h o i : e i s, u g g e s t i l g l l i t s t ( ' r c l i l l è r ' e r r t i a t i o t r r ' : r t e i iar g
r cr le a t e r n u n r b c l o l ' a r n e l o l t l a s t s : r t : t i r r a t r tgt ti r t t r t i t l r c .
'l
.rrttse
l r t ' s l r r r l t e r t i r l t ' o l m o l a l c r o u n l i r r m a t i o n ( ' s t i l r r a t e di n p r e v i o t t s u , o r k s l i r r I t . h o i . ç t i
I
I
r
p
e
r
t
h
ick
t
t
c
g
l
e
c
t
e
c
l
.
p l i r r t i p a l l r b t ' c a r r s ct h e l l r s t p c r i r . , col 1 ' t i r n eo 1 ' c r o u n l i r r n t a t i o t r n a s
lts
rlot
l)c
srlcll
it
rvoulcl
r'rrrnrcl clors not secnr to ltc ltlest'nt tn P. atthiopicl,r'atrclperhitlts
T
h
c
\
l
a
r
t
i
n
i
l
9
t
]
8
a
.
ô
r
.
r : \ n a l ) ( ) n r o r ' y ; l l r rl i r l t l r c [ t a r u n l h r o l a c. rl a c l ca s p r o p o s e c lb r ' ( i l i n t ' &
\atullillr
ï ' . r t t l l r i t t l i r ' t tIi ) u t l r \ \ r r \i n t o o t h c l c v c l o p m e n t i s s h u l c c ll r v o t l r c l P a r a n ! l t r o p u . ; 1 t e t ' i e s l t r t c l t ' a n l r t '
l9fltlû \cvelthelt'ss il this
:('cn ir: s\nill)onroll)hr. us suggcstcdl)\' (irirrt' & \lartin
: \ n u l ) ( ) n r ( ) r ' l ) h ra n c l t l r c p r o p o s i t i o r to f ' : r s e l e c t i o nt o l i r r m t e e t h c l L r i c k l r''l l t ' r ' t r o t t & \ \ ' r l o c l ,
. o i . r r rs, i n c c t h c l i r l m c r u i t h a
l ! ) 8 7 l l t ' r ' c r u i r r e c l .P . a t l h i o p i t u sc : l n n o t l r e a n a r r c c s t o ro 1 - 1 ' ô
l i L ' r t ' rc' l i l l i ' r ' t ' n t i u t i o rrt: r t c \ \ ' o r i l d b c m o r e s p e ti a l i z c d t h a n t l r c s c c o n d .
Acknowledgements
J r L l r . a ; u t r : l i rtlo P . P i c k a n d ( 1 . l ) c a n l o r i n s t l u c t i v r i i c ' l v i c ea n d s u g g e s t i t ) nosl l t h i s p t t p c r ' .r \ .
alrout
attcl t:t-,t'tttttt'ttts
-\lrrrrr. -\L Lurnpl:ind.J. \longe arc thallkccl lbr interesting clist:ussions
r l r i . \ \ ( ) r k . [ ' l r l t i c r r l : r rt h a n k s l n u s t l ) e c r p r e s s e dt o \ ' . ( i o p p e n s f o r c n a b l i r ] g m c t o s t u d v t l i c
r , r ' i q i r r ririlr s s i rl n u t e r i a li n h i s c a l c . I t h a n k a l l t h o s en ' h o h e l p e c ln r e u ' i t h t l i e l i n g l i s h , e s p e c i a l l v
. \ . - \ 1 r ' l 1 . s r r g . ' l ' h i s t u c l r ' ' " v alsu n d c d b r ' : r q ' r n n t l i t - , n rt h c l ' \ ' S S E N l " r t u t t c l i t t i o r t .
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( i t r 1 1 1 r c t t s . \ - . , l 9 l l 9 . H o r n i r tr ri rol l L r l i o r i r r r rlcl rl t c r o i u t i o n o l t h t l r r r i r o n n r t r r t . O t v l 4 r l : t 7
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l 62r.l . r l
Dcarr. -\1.
I ) , , l u l i t r t u t t l l i t l u n , , / l l u R l h u , l . l u t l r u h t l i l l m i n t ' . p i r . { l } 5 1 3 .\ o r \ - o r k : . \ l t l i n r r l t ( ; r L l \ t ( r .
I ) t a r r . - \ [ . ( ] . l 9 t t ! ) I I r c r l c r t l o p i r r g r l c r r t i l i o n; r n c ll o o t l r \ t l r r ( t u r ( i r r h o r r r i r r i r l sI .' r , l t ul t r i n u t . 5 3 , I { j 0 I 7 t j .
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