New evidences of Silurian Phyllocarid Crustaceans from SW Sardinia

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Bollettino della Società Paleontologica Italiana, 44 (3), 2005, 255-262. Modena, 30 novembre 2005
New evidences of Silurian Phyllocarid Crustaceans from SW Sardinia
Maurizio GNOLI & Paolo SERVENTI
M. Gnoli, Dipartimento del Museo di Paleobiologia e dell’Orto Botanico, Università di Modena e Reggio Emilia, Via Università 4, I41100 Modena, Italy; [email protected]
P. Serventi, Dipartimento del Museo di Paleobiologia e dell’Orto Botanico, Università di Modena e Reggio Emilia, Via Università 4, I41100 Modena, Italy; [email protected]
KEY-WORDS - Crustacea, Phyllocarida, Silurian, Abdominal somites, Telson, Mandibles, SW Sardinia, Italy.
ABSTRACT - Phyllocarid remains consisting of abdominal somites, caudal parts and secondarily phosphatized mandibles, from
Silurian of SW Sardinia are described and illustrated. Some material described and left in open nomenclature by Gnoli & Serpagli
(1984) is also reconsidered under Warneticaris cenomanensis (Tromelin, 1874). Other taxa like Ceratiocaris (Bohemicaris) bohemica
(Barrande, 1872), C.? (B.) sp. ind. cf. bohemica Barrande, 1872, C. (C.?) cf. cornwallisensis damesi Chlupáè, 1963, and Warneticaris
sp. ind. cf. W. cenomanensis (Tromelin, 1874) are also documented.
RIASSUNTO - [Nuovi resti di fillocaridi (Crustacea, Artropoda) nel Siluriano della Sardegna sudoccidentale] - Dopo la prima
descrizione e illustrazione di resti di fillocaridi provenienti dalla Sardegna sudoccidentale al limite Siluriano/Devoniano, avvenuta nella
prima metà degli anni ottanta, ne viene presentata una ulteriore. Tutti gli esemplari esaminati provengono dalla Formazione di
Fluminimaggiore e mostrano un eccellente stato di conservazione in quanto si presentano in tre dimensioni. Sulla base dei dati
sedimentologici è possibile dedurre un ambiente deposizionale di mare poco profondo, normalmente ossigenato e sottoposto a moto
ondoso nelle sue parti più elevate mentre era anossico nelle zone più profonde. Dallo studio dei nuovi campioni, costituiti da segmenti
addominali, parti caudali ed altre mandibole fosfatizzate, vengono documentati i seguenti taxa, Ceratiocaris (Bohemicaris) bohemica
(Barrande, 1872), C.? (B.) sp. ind. cf. bohemica Barrande, 1872, C. (C.?) cf. cornwallisensis damesi Chlupáè, 1963, e Warneticaris sp.
ind. cf. W. cenomanensis (Tromelin, 1874). A questi si aggiunge il materiale già descritto e lasciato in nomenclatura aperta da Gnoli &
Serpagli (1984), qui considerato appartenere a Warneticaris cenomanensis (Tromelin, 1874).
INTRODUCTION
During the past three decades paleontological
investigations and accurate sampling of Silurian
sections, carried out by a team of the Dipartimento del
Museo di Paleobiologia e dell’Orto Botanico (Università
di Modena e Reggio Emilia), have supplied a rich
collection of fossils including phyllocarid remains. Some
of these specimens were illustrated twenty years ago
by Gnoli & Serpagli (1984). However, the most
important discovery on this topic is due to Hamman et
al. (1990) who demonstrated that the “phyllocarids”
of the so called «phyllocarid beds of Taricco (1922)»
actually belong to «an unusual trilobite-like arthropod»
named Tariccoia arrusensis, later regarded as a true
trilobite of the Nectaspida Order (Hamman & Leone,
1997).
The new phyllocarid remains, all collected from the
Fluminimaggiore Formation, consist of three
fragmentary specimens with abdominal segments
(preserved in three dimensions), a dozen caudal parts
and several fragments and/or whole specimens of
secondarily phosphatized mandibles that commonly
occur in the acid-resistant residues of conodont
samples.
Information on Lithostratigraphic units of SW
Sardinian Silurian-early Devonian rocks, including the
phyllocarids-bearing beds, and biostratigraphy of the
key-section «Mason Porcus» can be found in Gnoli et
al. (1988, 1990) and in Ferretti & Serpagli (1996).
ISSN 0375-7633
Updated information on the lithology, palaeontology and
environment of the Fluminimaggiore and Mason Porcus
Formations in the locality Perd’e Fogu near
Fluminimaggiore and Argiola can be found in Serpagli
(1998), Ferretti et al. (1998a, b), and Corradini et al.
(1998a, b).
The Sardinian localities where phyllocarid remains
were found are summarised in Fig. 1. The Tab. 1 shows
the phyllocarid remains recovered in Silurian sections
or displaced blocks, with the age (biozones) and the
lithology related to the reported samples.
SOME REMARKS ON PHYLLOCARID
PALEOECOLOGY AND BIOSTRATIGRAPHY
The lithology of displaced blocks bearing phyllocarid
remains, deduced from investigations on sedimentary
structures and associated fauna (Ferretti, 1989)
indicates a shallow sea shelf normally oxygenated in
its upper parts and anoxic towards the bottom (Gnoli
et al., 1980).
This shelf, reworked by wave motion, developed in
a shallow basin, stirred by currents in its upper part
(Fluminimaggiore and Mason Porcus Formations (Gnoli
et al., 1990)), where, during Pøídolí-early Devonian
time, pelagic-type sediments were formed (Gnoli, 1985).
Apparently, Silurian phyllocarids do not characterize
a specific environment, being present either in the more
shallow marine facies (poorly washed biomicrite) or in
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Bollettino della Società Paleontologica Italiana, 44 (3), 2005
Fig. 1 - Location of the Sardinian fossiliferous localities in which
phyllocarid remains have been collected.
the relatively deeper ones. Telson parts - sometimes
with parallel orientation probably stirred up by current
- are the most common phyllocarid fragments. On the
contrary, abdominal somites are rare with only three
specimens recovered so far. This environmental setting
added to the good preservation of the majority of the
fossils would suggest short and slight transport on a
typically muddy bottom.
The paleoecological analysis of the associated fauna
does not help much in clarifing the paleoenvironmental
setting because it is mainly represented by orthoconic
nautiloids occurring only in some horizons of scattered
sequences (i.e. «Argiola» ARG-BK 15). Phyllocarid life
habits have been described in details (e.g. Chlupáè,
1994; Vannier et al., 1997) taking into account their
adaptation to dysaerobic bottom conditions.
The use of phyllocarids as stratigraphic tools is due
to Chlupáè (1994) who carried out a revision and a
general synthesis on the biostratigraphy of Bohemian
phyllocarid. The age of phyllocarid remains in SW
Sardinia, has been mainly deduced by means of the
associated conodonts (Tab. 1) found in the acidresistant residues of the blocks and/or sequence samples
by several authors (Serpagli, 1971; Serpagli &
Mastandrea, 1980; Olivieri & Serpagli, 1990; Olivieri
et al., 1981; Mastandrea, 1985; Gnoli et al., 1988;
Ferretti et al., 1998; Corradini et al., 1998; Corradini &
Serpagli, 1998, 1999; Serpagli & Corradini, 1999). Also
other index fossils, like graptolites, have been sometime
Tab. 1 - Distribution of taxa in the samples bearing phyllocarid remains: age (biozones) and lithology. Abbreviations: BK = displaced
block; ARG = «Argiola» section, MP = «Mason Porcus» (House of pigs) section, SF = Fluminimaggiore path section, GALE =
«Galemmu», PF = «Perd’e Fogu» (Fire Stone). Conodont biozonation according to Corradini & Serpagli (1998-99). * After Jaeger (pers.
comm., letter of July 20th, 1987).
M. Gnoli, P. Serventi - Silurian Phyllocarids from SW Sardinia
used. The Sardinian conodont biozones are those
defined by Corradini & Serpagli, (1998, 1999).
SYSTEMATIC DESCRIPTIONS
All the material studied is housed in Paleontological
Collection of the Dipartimento del Museo di
Paleobiologia e dell’Orto Botanico under the Cat. nos.
IPUM 19801, 19836, 24236-24246.
Order PHYLLOCARIDA Packard, 1879
Suborder CERATIOCARINA Clarke, 1900
Family CERATIOCARIDIDAE Salter, 1860
Genus Ceratiocaris Mc Coy, 1849
Type-species - Ceratiocaris solenoides Mc Coy,
1849; Miller, 1889 by subsequent designation.
Subgenus Ceratiocaris (Bohemicaris) Chlupáè, 1994
Type-species - Ceratiocaris bohemica Barrande,
1872, by original designation, Chlupáè, 1994, p. 14.
Ceratiocaris (Bohemicaris) bohemica (Barrande,
1872)
(Figs. 2a-i)
1984 Ceratiocaris cf. bohemica Barrande, 1872 - G NOLI &
SERPAGLI, p. 258, figs. 1, 15.
1994 Ceratiocaris (Bohemicaris) bohemica CHLUPÁ È , pp. 5,
14; Pl. 1, figs. 1-6.
1994 Ceratiocaris (Bohemicaris) bohemica Chlupáè RACHEBOEUF, pp. 289-291, text-figs. 3B, 5.
Material - Two specimens with fifth, sixth and
seventh abdominal somites with poorly preserved
caudal part (IPUM 24236 and unfigured 24246) plus
various fragments of telsonal part with furcal rami
(IPUM 24242, 24243, and unfigured 24244).
Description - All the abdominal somites preserved
were compacted; furthermore the fifth one preserves
only its terminal part, but unlike the sixth and seventh
ones that are apparently smooth, it bears an
ornamentation consisting of longitudinal ribs that run
roughly parallel to the axis of the segment and are distally
anatomised (see Barrande, 1872, pl. 19, fig. 2 and
present paper, Fig. 2a). In a small area of this
ornamentation it is possible to distinguish very thin,
small (0.27 to 0.12 mm in length) very characteristic,
slit-like or long comma-like depressions (Fig. 2b’)
slightly oblique to the ribs. Their length varies from
corresponding to about 1/3 to 1/2 of the distance
between ribs, that is 0.3 mm. The probable function of
these depressions is discussed in the following remarks.
The abdominal somites are 15, 26 and 34 mm long
respectively. Caudal parts are very fragmented.
One specimen (IPUM 24243) consists of a fragment
of telson and two fragments of the furcal rami arranged
sub-parallel to each other in the sediment. The telson
shows a sub-polygonal cross section in its middle part
where it corresponds to 5.5 mm in lateral width; as
257
can be seen in Fig. 2g, there are 9 longitudinal ridges
that run along its whole length: one on the dorsal side,
two orders of dorso-lateral, and two dorso-ventral
between which there are slightly concave depressed
areas. Between the dorso-lateral ridges, several subelliptic alveoli are present for bristle insertion. The alveoli
diameters are about 0.8 and 0.7 mm, the distance
between them is quite regular and they are placed about
2.2 mm apart. In the studied material the bristles are
never preserved. The furca rami are also polygonalrounded in cross-section, depressed and bearing 10
longitudinal ridges in their proximal part, whereas
distally the ridges become rounded so they probably
terminate with a fairly sub-elliptic or lens-shaped crosssection. Another specimen (IPUM 24242) from the
same displaced block (ARG-BK 15) bears three strongly
damaged fragments of caudal parts: two of telson and
a ramus of furca not preserved in anatomical position.
These caudal parts are 59, 27 and 9 mm long
respectively and show the same features belonging to
the same species as above. A further caudal fragment,
38 mm long in the counterpart, showing the same
morphology as above reported, is that from level 2b of
the Mason Porcus section (IPUM 24244).
Remarks - The ornamentation of the fifth abdominal
somite previously described and, in particular, the
presence of the very small depressions (Fig. 2b’) could
represent slits of probable sensory terminations below
the exoskeleton for possibly sensing environmental
variations (physical and/or biological). Their actual
function remains unknown. These morphological
peculiarities were never previously reported with the
exception of Vannier et al. (1997), who figured
something similar feature (Vannier et al., 1997, fig. 9B)
from the right pleural fold of the Devonian
archaeostracan phyllocarid Rhinocaris columbina
Clarke in Hall & Clarke 1888.
Ceratiocaris? (Bohemicaris) sp. ind. cf. bohemica
(Barrande, 1872)
(Figs. 3a-b)
Material - Sixth, seventh abdominal segment
exoskeletal parts and telson head (IPUM 24241).
Abdominal somites are shifted over each other rather
than squeezed and probably not anatomically jointed to
a telson head for a total length of 53 mm in a little
displaced block (probably coming from level 5 of the
Mason Porcus section).
Description - The specimen IPUM 24241 shows
the sixth and seventh abdominal somites displaced from
the anatomical position probably due to compaction of
the muddy sediment. However, these preserve a peculiar
ornamentation consisting of sub-parallel ribs oblique
to the axis of the somites (about 45 degrees). This can
be identified as the proximal part of the last abdominal
somite where the ribs form a concentric botroidal
pattern of ornamentation as shown in Fig. 3b. The
telson head, which is the largest one among all
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Bollettino della Società Paleontologica Italiana, 44 (3), 2005
specimens so far found in Sardinia (12.5 mm in width),
bears as ornamentation fine oblique ridges disappearing
posteriorly.
Remarks - This poorly preserved material does not
allow more detailed taxonomic studies. This sample
represents the third abdominal segment exoskeletal part
ever recovered from Sardinia.
Fig. 2 - Ceratiocaris (Bohemicaris) bohemica (Barrande, 1872).
a) Upper view of the whole specimen (No. 24236). Scale bar = 20 mm;
b) fifth segment showing sub-parallel wrinkled pattern of ornamentation of the same specimen. Scale bar = 10 mm;
b’) particular enlarged to show the very small slit-like structures between the ribs forming ornamentation of the same specimen. Scale
bar = 5 mm (see text for interpretation);
c) upper view of the sixth abdominal somite of the same specimen. Scale bar = 5 mm;
d) upper view of the seventh abdominal somite of the same specimen. Scale bar = 20 mm;
e) poorly preserved caudal part of the same specimen. Scale bar = 20 mm;
f) upper view a couple of telsons (T) and a furcal ramous (Fr) of No. 24242 specimen. Scale bar = 10 mm;
g, h) telson and furcal rami of another specimen (No. 24243) showing their polygonal cross-sections (pentagonal the telson, more
complex and rounded the (h) furcal rami). Scale bar = 15 mm;
i) the same specimen in perspective view (note the alveoli for bristle insertion). Scale bar = 5 mm;
Note: the left furcal ramus cross-section of Fig. 3h is figured reflecting the right one horizontally because specimen No. 24243 is not so
well preserved.
M. Gnoli, P. Serventi - Silurian Phyllocarids from SW Sardinia
259
Remarks - Since the surface of the lower part of
the telson, just after the telson head between the two
ventro-lateral ridges, is moderately concave, (Fig. 4d),
we prefer to leave this form in open nomenclature. This
species is reported here for the first time from Sardinia.
Genus Warneticaris Racheboeuf, 1994
Type species - Ceratiocaris cenomanense Tromelin,
1874 by subsequent designation, Racheboeuf, 1994.
Warneticaris cenomanensis (Tromelin, 1874)
(Figs. 5a-c)
Fig. 3 - Ceratiocaris? (Bohemicaris) sp. ind. cf. bohemica
(Barrande, 1872) (No. 24241).
a) Lateral view of the whole specimen, scale bar = 10 mm;
b) close-up of the same specimen to show ornamentation of the
seventh somite, scale bar = 5 mm.
Subgenus Ceratiocaris (Ceriatocaris) McCoy, 1849
1874 Ceratiocaris cenomanense T ROMELIN in Gullier &
Tromelin, p. 590.
1876 Ceratiocaris cenomanensis Tromelin - T ROMELIN &
LEBESCONTE, p. 651.
1886 Ceratiocaris cenomanensis Tromelin - GUILLIER, p. 54.
1935 Ceratiocaris cenomanense Tromelin - PÉNEAU, p. 551.
1984 Ceratiocaris sp., GNOLI & SERPAGLI, p. 260, figs. 2a-d.
1994 Warneticaris cenomanensis (Tromelin) - RACHEBOEUF, pp.
287-289; Pl. III, figs. 1-11; Pl. IV, figs. 1-2; text-figs. 3D,
4.
Material - Left side of the last (seventh) abdominal
somite and proximal part of telson (IPUM 19836) for a
total length of 31 mm (already published by Gnoli &
Serpagli (1984) and left in open nomenclature as
Ceratiocaris sp.).
Type-species - Ceriatocaris solenoides McCoy,
1849.
Ceratiocaris (Ceriatocaris?) cf. cornwallisensis
damesi Chlupáè, 1963
(Figs. 4a-d)
1886 Ceratiocaris damesi NOVÁK, p. 676 (nomen nudum).
1963 Ceratiocaris cornwallisensis damesi CHLUPÁè, pp. 104108; Pl. 12, figs. 9-10; Pl. 14, figs. 3-5; Pl. 15, figs. 1-4;
text-figs. 3-5.
Material - Telson (IPUM 24237) with 45 mm long
broken tip (reaching 53 mm in the counterpart) from
level 5 of the «Mason Porcus» section.
Description - The well preserved telson (Figs. 4ad) shows two rows of alveoli for the insertion of bristles
in the dorso-lateral ridge. Eleven symmetrical alveoli
are preserved on both sides, showing an elliptical shape;
they are regularly spaced 2.33 mm apart (Fig. 4c), the
axes of which are 0.66 mm and 0.4 mm. In crosssection, towards the lower part after the ridges bearing
alveoli there are two concave areas, followed by two
ventro-lateral ridges ending with a ventral platform. The
latter protects ventrally the articulation of the furca (Fig.
4b). The telson head is hemispherical in shape and bears
an ornamentation consisting of fine radiating lirae. In
its central part the cross-section is sub-pentagonal in
outline and from each corner originates five longitudinal
rounded ridges, which reduce to four towards its apical
part (as reported by Chlupáè, 1963, p. 106, text-fig. 4;
and Rolfe, 1963, p. 487, text-fig. 1; see also Fig. 4d in
this paper).
Fig. 4 - Ceratiocaris (Ceratiocaris?) cf. cornwallisensis damesi
Chlupaè, 1963 (No. 24237).
a) Dorsal view of the telson;
b) lateral view of the telson showing the ventral recumbent
protection to the articulation for the furcal rami movement;
c) close-up of dorso-lateral view for bristle insertion;
d) schematic proximal, distal, and terminal telson cross-sections.
All scale bars = 10 mm.
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Bollettino della Società Paleontologica Italiana, 44 (3), 2005
of this section had already been described by Gnoli et
al. (1988).
According to P. Racheboeuf (letter of February 25th,
2004), the specimen described by Gnoli & Serpagli
(1984), «… could probably belong to a new genus
because of the shape of the telson, with a sub halfrounded head in cross-section, becoming triangular
posteriorly, and also because the morphology of the
furca do not fit in with Ceratiocaris». Chlupáè (1985,
personal comm.) suggested that the Sardinia
Ceratiocaris sp. could be close to grata and perhaps
classified as C. cf. grata. In addition, Racheboeuf (1994,
p. 287) assigned the Bohemian Ceratiocaris grata
Chlupáè, 1984, to his new genus Warneticaris
suggesting that grata is the most closely allied to
cenomanensis.
On the basis of the aforementioned remarks and
after careful restudy of the 1984 specimen (previously
left in open nomenclature), we prefer to assign this
form to Warneticaris cenomanensis (Tromelin, 1874).
Warneticaris sp. ind. cf. cenomanensis (Tromelin,
1874)
(Figs. 6a-e)
Fig. 5 - Warneticaris cenomanensis (Tromelin, 1874) (No. 19836).
a) Dorsal view of the whole specimen. Scale bar = 10 mm;
b) enlargement of the last pleonite showing ornamentation by
triangular scales and the telson head of the same specimen in
dorso-lateral view with ornamentation represented by oblique
fine V-shaped short striae. Scale bar = 5 mm;
c) left lateral view of the telson of the same specimen showing
oblique lateral ridge and the left row of alveoli for bristle
insertion. Scale bar = 7.5 mm.
Description - The last abdominal segment bears a
characteristic ornamentation mainly consisting of
triangular, apparently imbricate scales (see comparable
features in Vannier et al., 1997, pp. 100-101, fig. 10)
like for the Palaeozoic archaeostracan phyllocarids. The
telson is triangular in cross-section and bears bilaterally
rows of sub-elliptic alveoli, just above the dorso-lateral
oblique ridges (about 0.2 mm wide, 0.6 mm long, and
distant 2.2 mm from each other) for bristles insertion.
Its ventral part shows longitudinal furrows, proximally
semicircular to rounded-triangular distally. The telson
head is sculptured by sub-triangular pattern of oblique
short lines. Posteriorly to its head, which is semicircular in cross-section, the telson bears ventro-lateral
apertures for the insertion and articulation of furcal
rami which are flattened, shorter than the telson and
lanceolate in shape. Unfortunately, only the left furcal
ramus is preserved in the specimen studied here.
Remarks - As for the abdominal segments (see
introductory part) - these exoskeletal parts are rather
rare, since only three have been so far recovered from
the «Mason Porcus» section. The lithology and fauna
Material - A triangular telson and furca, 73 mm
long in cross-section (IPUM 24238), from level 5 of
the Mason Porcus section.
Fig. 6 - Warneticaris sp. ind. cf. cenomanensis (Tromelin, 1874)
(No. 24238).
Figs. a-c, scale bar = 15 mm.
a) Dorsal view of the telson;
a’) schematic middle telson sub-triangular cross sections;
b) the same telson in lateral view;
c) the same in ventral view;
d) furcal rami of the same telson in upper view. Scale bar = 25
mm;
e) close up of the left ventral ridge counterpart showing the row
of very little alveoli close to each other for fine bristle insertion.
Scale bar = 25 mm.
M. Gnoli, P. Serventi - Silurian Phyllocarids from SW Sardinia
Description - The 62 mm long telson (with
incomplete tip), reaching 73 mm in the counterpart and
13 mm in width, shows the typical features of W.
cenomanensis. However, in lateral view the telson is
not straight, but gently curved upwards distally (Fig.
6b). Size and ornament are also completely different in
the two forms.
The dorso-lateral ridges are not clearly preserved
as well as the ventral platform recumbent posteriorly
to protect the furcal rami articulation. The alveoli for
bristle insertion are clearly visible only in the
counterpart of one of the two ventral ridges that run
symmetrically along the whole ventral part of the telson
The alveoli are very small (about 0.15 mm of diameter),
close to each other and circular in shape (Fig. 6e).
Remarks - The large size of the Sardinian telson
implies that it probably belonged to either an adult or a
gerontic specimen.
This form is compared in its general shape to W.
cenomanensis, but lateral and ventral ridges are sharp
and not rounded as it appears in the reconstruction of
Racheboeuf (1994, fig. 4B). Furthermore, the
incomplete preservation of the material studied also lead
us to leave this form in open nomenclature.
ACKNOWLEDGEMENTS
Thanks are due to the late Dr. Ivo Chlupá è (Charles
University, Prague, Czech Republic), for useful discussion and
suggestions on the first proofs of the paper. This work benefits
also by from the expertise of Prof. Patrick R. Racheboeuf
(Université de la Bretagne occidentale, Brest, France) and his
profitable experience on the topic. Many thanks to Prof. E.
Serpagli and Prof. C. Corradini for their help on updated conodont
biostratigraphy. We thank also Prof. J. Vannier (Université Claude
Bernard, Lyon, France) for his valuable help in improving our
manuscript.
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Manuscript received 18 March 2005
Revised manuscript accepted 10 November 2005