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The rediscovery and redescription of the
holotype of the Late Jurassic turtle
Plesiochelys etalloni
Submitted 19 December 2013
Accepted 13 January 2014
Published 6 February 2014
Corresponding author
Jérémy Anquetin,
j.anquetin@gmail.com
Academic editor
Andrew Farke
Additional Information and
Declarations can be found on
page 14
DOI 10.7717/peerj.258
Copyright
2014 Anquetin et al.
Distributed under
Creative-Commons CC-BY 3.0
OPEN ACCESS
Jérémy Anquetin1,2, Sylvie Deschamps3and Julien Claude4
1Section d’archéologie et paléontologie, Office de la culture, République et Canton du Jura, Porrentruy,
Switzerland
2UMR CNRS 7207 MNHN UPMC, Muséum national d’Histoire naturelle, Paris, France
3Musée d’Archéologie du Jura, CCE René Rémond, Lons-le-Saunier, France
4Institut des Sciences de l’Evolution de Montpellier, UMR 5554 CNRS, Montpellier, France
ABSTRACT
Plesiochelyidae are a major component of Late Jurassic shallow marine environ-
ments throughout Europe. However, the taxonomy of plesiochelyid turtles is rather
confused. Over the years, many taxa have been synonymized with Plesiochelys
etalloni, one of the first described species. However, the holotype of P. etalloni (and
only specimen known from Lect, the type locality) was lost for more than 150 years.
This specimen has been recently rediscovered in the collections of the Musée
d’archéologie du Jura in Lons-le-Saunier, France. For the first time since its origi-
nal description in 1857, the holotype of P. etalloni is redescribed and compared to
relevant material. The taxonomic status of this taxon is revised accordingly. Based on
the morphology of the newly rediscovered holotype and on a reassessment of speci-
mens from Solothurn (Switzerland), the species P. solodurensis,P. sanctaeverenae and
P. langii are synonymized with P. etalloni. Known skull-shell associations for P. etal-
loni are re-evaluated in light of the new morphological information available since
the rediscovery of this holotype specimen. Finally, we confirm that Plesiochelys is
represented by a single species in the Late Jurassic of the Jura Mountains.
Subjects Evolutionary Studies, Paleontology, Taxonomy
Keywords Plesiochelys, Plesiochelyidae, Testudines, Kimmeridgian, Tithonian, Late Jurassic, Switzerland,
France
INTRODUCTION
Despite numerous historical discoveries dating from as early as the beginning of the
nineteenth century (e.g., Cuvier, 1824;Pictet & Humbert, 1857;von Meyer, 1860;Pictet,
1860;Wagner, 1861;Maack, 1869;Rütimeyer, 1873), the diversity of Late Jurassic
European turtles still eludes our understanding. Traditionally referred to the families
Plesiochelyidae Baur, 1888, Thalassemydidae Zittel, 1889, and Eurysternidae Dollo, 1886,
these forms are generally considered to be basal eucryptodires, but their exact
relationships with one another and with other turtle groups remain largely unclear and
usually vary among authors (e.g., Gaffney & Meylan, 1988;Hirayama, Brinkman &
Danilov, 2000;Gaffney et al., 2007 ;Joyce, 2007;Sterli, 2010;Rabi et al., 2013). A number
of reasons may be invoked to explain this situation, but at least two of these are the much
How to cite this article Anquetin et al. (2014), The rediscovery and redescription of the holotype of the Late Jurassic turtle Plesiochelys
etalloni.PeerJ 2:e258; DOI 10.7717/peerj.258
needed revision of the rich historical material and the limited number of skull-shell
associations. Cranial characters are important for turtle systematics, yet many Late
Jurassic turtles from Europe are known from postcranial or cranial material only. There
are few exceptions however, for which both the skull and the shell are well known: notably
Solnhofia parsonsi Gaffney (1975b) and Plesiochelys etalloni (Pictet & Humbert, 1857).
Emys etalloni Pictet & Humbert (1857) was described based on a single shell found in
the French Jura Mountains (see below). A few years later, Rütimeyer (1873) reassigned
this species to his newly created genus Plesiochelys. The type species of Plesiochelys is P.
solodurensis Rütimeyer (1873), a species typified based on material from the prolific
quarries near Solothurn in the Swiss Jura Mountains. Rütimeyer (1873) and Bräm (1965)
afterwards both recognized the presence of P. solodurensis and P. etalloni in the Solothurn
deposits. Although turtle skulls were known in Solothurn since as early as the 1820s
(Cuvier, 1824; see Bräm, 1965 for an historical account), they were not fully prepared until
the 1970s (Gaffney, 1975a). Based on this material, Gaffney (1975a) concluded that Emys
etalloni Pictet & Humbert (1857),Emys jaccardi Pictet (1860) from the Late Jurassic of Les
Hauts-Geneveys (Canton of Neuchâtel, Switzerland), Stylemys lindenensis Maack (1869)
from the Kimmeridgian of Hanover (Germany), as well as Plesiochelys solodurensis
Rütimeyer (1873),Plesiochelys sanctaeverenae Rütimeyer (1873),Craspedochelys picteti
Rütimeyer (1873), and Craspedochelys crassa Rütimeyer (1873) from the late
Kimmeridgian of Solothurn (Canton of Solothurn, Switzerland) represented a single
species, which should be named Plesiochelys etalloni (Pictet & Humbert, 1857) in
application of the Principle of Priority. The immediate effect was that P. etalloni was
henceforth included into phylogenetic analyses, which helped to improve our
understanding of the systematics and relationships of Late Jurassic and Early Cretaceous
turtles from Europe and Asia (e.g., Gaffney & Meylan, 1988;Hirayama, Brinkman &
Danilov, 2000;Joyce, 2007). However, this relatively inclusive synonymy list was not
generally accepted among specialists (including ourselves). For example, several
subsequent authors still considered C. picteti,C. jaccardi,P. etalloni, and P. solodurensis as
different species (e.g., Antunes, Becquart & de Broin, 1988;Lapparent de Broin,
Lange-Badré & Dutrieux, 1996).
This extremely confusing situation is in part due to the fact that the holotype of
Plesiochelys etalloni was considered to be lost since the 1860s and was therefore
unavailable notably to Rütimeyer (1873),Bräm (1965),Gaffney (1975a), and Lapparent de
Broin, Lange-Badré & Dutrieux (1996). These authors based their conclusions on the
original description (Pictet & Humbert, 1857) and on plaster casts of the type specimen.
These casts are available in several European museums, notably in Paris, Geneva,
Lons-le-Saunier, Montbéliard, and Besançon, but they differ among each other regarding
quality and completeness. Some of these casts lack the pygal region of the carapace (e.g.,
the Geneva copy), whereas others only consist of a cast of the carapace (e.g., the
Montbéliard copy). They do not allow a precise examination of sutures and sulci,
especially on the carapace where some sutures must be determined from their imprints
on the sediment. In contrast, we have been fortunate to locate this historical specimen in
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 2/17
the collections of the Musée d’archéologie du Jura in Lons-le-Saunier, France. We have
also been able to retrace the history of this specimen as it passed from one owner to the
other. This material is redescribed herein and the taxonomic status of Plesiochelys etalloni
is revised accordingly. This specimen also gives us the opportunity to reassess the validity
of several species from the Late Jurassic of the Jura Mountains. Finally, this rediscovery
allow us to re-evaluate the known skull-shell associations for P. etalloni.
Institutional abbreviations: MAJ, Musée d’archéologie du Jura, Lons-le-Saunier,
France; MH, Naturhistorisches Museum, Basel, Switzerland; NMS, Naturmuseum
Solothurn, Switzerland.
HISTORICAL BACKGROUND
Pictet & Humbert (1857) explained that the holotype of Plesiochelys etalloni was collected
by a local priest in the forest close to the village of Lect, near Moirans-en-Montagne (Jura,
France). When they studied the specimen, it was in possession of Joseph Célestin Girod,
vicar general of the Saint-Claude diocese (France). Neither Rütimeyer (1873) nor Bräm
(1965) gave indication relative to the repository of this specimen. Gaffney (1975a)
indicated that H. Bräm told him the specimen was lost. Lapparent de Broin, Lange-Badré
& Dutrieux (1996) explained that they actively looked for the type without success, but
they figured the plaster cast housed in the Natural History Museum in Geneva,
Switzerland. Finally, without further explanation, Lapparent de Broin (2001) stated that
the holotype of P. etalloni had been located in the Natural History Museum of Besançon,
France. After verification, it appears that this information is incorrect.
One of us (SD) rediscovered the original specimen a few years ago in the collections of
the Musée d’archéologie du Jura in Lons-le-Saunier, France. Examination leaves no doubt
whatsoever on the identity of this specimen (Figs. 1 and 2). This specimen (MAJ
2005-11-1) was not always housed at the MAJ: it was donated to the museum by a private
owner in 1994. The MAJ also houses a plaster copy of the fossil, which was offered by C-A
Etallon, the renowned geologist, on March 30th, 1857. After a careful investigation, we
were able to uncover most of the history of the fossil shell before it was finally donated to
the MAJ.
The claim that the holotype of P. etalloni was housed in the Natural History Museum of
Besançon (Lapparent de Broin, 2001) is not entirely incorrect. We have found evidence
that the specimen was actually part of the Besançon Museum collection, if only for a
short time. This part of the story can be followed in the Mémoires de la Société d’émulation
du département du Doubs dated from 1859 and 1860. Bishop Mabile, Vicar Girod’s
superior, offered the specimen to Mr Thiébaud, a member of the Société d’émulation du
Doubs (a French scientific society), who gave it to the Besançon Museum. The exact date
is unclear, but it was sometime between 1857 and 1859. In 1859, Vicar Girod wrote to the
French Minister of Public Education and Cults, who turned him down, then to the Rector
explaining that he had never agreed for the fossil to be given for free to the Besançon
Museum and claimed property on the specimen. The Rector abided and the holotype of
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 3/17
Figure 1 Specimen mounted on a wooden pedestal. MAJ 2005-11-1, holotype of Plesiochelys etalloni
(Pictet & Humbert, 1857 ). Specimen mounted on a wooden pedestal with the old label ‘‘Emys etalloni,
(Pictet et Humbert) - Portland - Moirans (Jura)’’. (A) carapace; (B) plastron. Note that the specimen is
upside down.
P. etalloni was sent back to Saint-Claude (Jura, France). Joseph Célestin Girod died in
1863 and the track of the specimen was lost.
The last piece of the puzzle was revealed when Mr and Mrs Lacroix donated the
specimen to the MAJ in 1994. After claiming the fossil as his own, the Vicar sold it to a
private party, the ancestor of Mr and Mrs Lacroix, in order to finance the renovation of
his church. The transaction must have occurred between 1859 and 1863. Until 1994, the
holotype of P. etalloni remained in this family and was passed from one generation to
another (Fig. 1).
SYSTEMATIC PALEONTOLOGY
TESTUDINES Batsch, 1788
EUCRYPTODIRA Gaffney, 1975c
PLESIOCHELYIDAE Baur, 1888
Remarks.—Late Jurassic eucryptodires from Europe are traditionally referred to one of
the three following families: Plesiochelyidae, Eurysternidae, and Thalassemydidae. These
names have been inconsistently, but regularly, used since the nineteenth century. Bräm
(1965) conceptualized these families as follows. Plesiochelyids were considered to be
characterized by a completely ossified carapace, an osseous bridge, and the absence of
lateral plastral fontanelles. Eurysternids were characterized by an incompletely ossified
carapace (presence of costo-peripheral fontanelles), a ligamentous bridge, and the
presence of both lateral and central plastral fontanelles. Finally, thalassemydids were
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 4/17
considered to retain costo-peripheral fontanelles and to lack lateral plastral fontanelles. In
addition to these characters, the presence of three cervical scales has been regularly
mentioned as a distinctive feature of plesiochelyids (e.g., Lapparent de Broin, Lange-Badré
& Dutrieux, 1996;Danilov, 2005;Pérez-García, in press), although some eurysternids are
known to share this characteristic (Bräm, 1965;Joyce, 2003;Anquetin & Joyce, in press).
This and other accumulating evidence (J Anquetin, unpublished data) suggest that the
three aforementioned families may actually form a monophyletic group. As such, the
definition of Plesiochelyidae is likely to change in the near future. That being said, we will
continue to use the traditional definition of Plesiochelyidae (sensu Gaffney, 1975a;
Lapparent de Broin, Lange-Badré & Dutrieux, 1996;Danilov, 2005) for the purpose of the
present study. Consequently, Plesiochelys etalloni is considered a member of the
Plesiochelyidae based on the presence of three cervical scales and the absence of
carapacial and lateral plastral fontanelles.
Plesiochelys Rütimeyer, 1873
Plesiochelys etalloni Pictet & Humbert, 1857
Emys Etalloni Pictet & Humbert, 1857 (original description)
Plesiochelys solodurensis Rütimeyer, 1873 (subjective synonymy)
Plesiochelys sanctaeverenae Rütimeyer, 1873 (subjective synonymy)
Plesiochelys langii Rütimeyer, 1873 (subjective synonymy)
Type material.—MAJ 2005-11-1, a shell missing a large part of the carapace medially.
Holotype by monotypy.
Type horizon and locality.—‘‘Forêt de Lect’’ (Lect is a small village) near
Moirans-en-Montagne (Department of Jura, France), Late Jurassic. The exact horizon is
uncertain, but most outcrops in the vicinity of Lect are either Kimmeridgian or early
Tithonian in age. According to Etallon (1857), the specimen was found in the ‘‘calcaires
portlandiens’’. Gravesia gigas was also found in these limestones (Etallon, 1857), which
led Lapparent de Broin, Lange-Badré & Dutrieux (1996) to conclude that MAJ 2005-11-1
was probably from the early Tithonian.
Illustrations of type.—(Pictet & Humbert, 1857: plates I-III); Figs. 1 and 2.
Referred specimens.—See Bräm (1965): specimens referred to P. etalloni,P.
solodurensis,P. sanctaeverenae. For cranial material, see Gaffney (1975a).
Revised diagnosis.—Species of Plesiochelyidae (sensu Gaffney, 1975a;Lapparent de
Broin, Lange-Badré & Dutrieux, 1996;Danilov, 2005) known from most of the skeleton.
Differing from P. planiceps (Owen, 1842) in the following features (see Gaffney, 1975a):
lingual ridge of maxilla usually lower than in P. planiceps; anterior portion of lingual ridge
on the lower jaw curving anteriorly (as opposed to medially in P. planiceps); at level of
vomer-premaxilla suture the distance between lingual ridges of maxillae is narrower than
in P. planiceps. Differing from all other Plesiochelys species in the following combination
of features: relatively large carapace (up to 550 mm in length); shell bones relatively thick;
carapace oval in outline; wide and shallow nuchal notch; additional trapezoidal element
often present between the neural series and first suprapygal; wide vertebral scales, usually
extending approximately half the length of the costals; anterior marginal scales very
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 5/17
Figure 2 Morphology of the holotype. MAJ 2005-11-1, holotype of Plesiochelys etalloni (Pictet & Humbert, 1857). (A) photograph of the carapace;
(B) interpretative drawing of the carapace; (C) 3D surface reconstruction of the carapace; (D) photograph of the plastron; (E) interpretative drawing
of the plastron; (F) 3D surface reconstruction of the plastron. Bones are white; stripped lines indicate internal bone layers; green solid lines indicate
scale sulci; matrix is gray. Abbreviations: ab, abdominal; an, anal; ce, cervical; co, costal; eg, extragular; epi, epiplastron; ento, entoplastron; fem,
femoral; gu, gular; hyo, hyoplastron; hypo, hypoplastron; hum, humeral; m, marginal; n, neural; nu, nuchal; p, peripheral; pect, pectoral; pl; pleural;
py, pygal; sp, suprapygal; v, vertebral; xi, xiphiplastron.
short and not extending onto costals; relatively long plastron (85–90% of carapace length)
sutured to the carapace along a long osseous bridge; entoplastron variable in size, usually
diamond-shaped with a more or less extended posterior part; hyoplastron and xiphiplas-
tron longer than wide; central plastral fontanelle retained in some adults; short gular
and extragular scales; gular-humeral sulcus reaching the anterior part of the entoplastron;
long humeral scale; four inframarginal scales mostly covering the plastral elements.
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 6/17
Remarks.—The synonymy list is intentionally restricted to the Plesiochelys species
described by Rütimeyer (1873) and later revised by Bräm (1965). The synonymy list
proposed by Gaffney (1975a) is more inclusive, but testing it would require an extensive
revision of historical material at the European scale, something that was done neither by
Gaffney (1975a),1976 nor any subsequent author (see Discussion) and that is beyond the
scope of the present study as well.
DESCRIPTION
General description
The holotype of Plesiochelys etalloni (MAJ 2005-11-1) is a large, oval shell with carapace
and plastron still articulated (Fig. 2 and Video S1). The specimen may have been slightly
flattened during fossilization, but there are no indications of severe deformation. The
specimen is fairly complete, although part of the left bridge and central part of the
carapace are missing. The part of the carapace that is missing reveals the steinkern, which
probably explains why the locals regarded this specimen as the imprint of a human torso
(Pictet & Humbert, 1857). There are some indications in the right axillary and inguinal
notches that some elements of the appendicular skeleton are preserved within the matrix,
but as it stands these elements are undetermined.
Carapace
As preserved, the length of the carapace is 471 mm, but most of the pygal is missing
(Figs. 2A–2C and S2). The carapace is evenly oval in outline, except anteriorly where
there is a broad, shallow nuchal notch. A large part of the carapace is missing centrally. As
a result, the neural series and the medial half of most costals are only visible as imprints
on the steinkern.
The nuchal is a wide and trapezoidal element. The nuchal notch is shallow, but it
extends laterally on the medial part of the first peripheral. Only the anterior part of the
first neural is preserved. This element was apparently longer than wide and rectangular.
Neurals 2–6 are preserved as imprints on the steinkern. They are elongate, hexagonal
elements with their shorter sides facing anteriorly. The sixth neural is shorter than the
previous elements in the series. Behind the sixth neural, the imprint of the anterior part of
the seventh neural is also preserved. Posteriorly, the steinkern is covered by the bony
carapace, but the sutures is this area are hardly visible and it is uncertain whether or not
there are additional elements to the neural series. Although it is impossible to be certain,
the eighth costals may contact one another in the midline. Most specimens from
Solothurn referred to P. etalloni (sensu this study) have an eighth neural and an additional
trapezoidal element of uncertain identity (additional neural, additional suprapygal, or
neomorphic bone) between the seventh neural and the first suprapygal. This area is
however relatively variable in plesiochelyids and other basal eucryptodires, and neurals 7
and or 8 may be reduced or lost allowing a medial contact of costals 7 and/or 8 (Bräm,
1965;Pérez-García, 2012; J Anquetin, unpublished data). There are eight pairs of costals.
The first costal is relatively short compared to the following ones. Anteriorly, it contacts
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 7/17
the nuchal and the three first peripherals. Costals 2–4 are wider and longer elements, with
costal 3 being notably wide distally. Costals 5–8 decrease progressively in length and
width. There were certainly 11 pairs of peripherals, even if they cannot be clearly all
observed on the fossil. The sutures between peripherals 4, 5 and 6 are not preserved
dorsally, but they are visible ventrally. Posteromedially, the suture between the tenth and
eleventh peripherals is not preserved. Peripherals are longer than wide, rectangular
elements. Most of peripheral 11 is missing on both sides. The posteromedial region of the
carapace is rather poorly preserved. There are two large suprapygals. The first suprapygal
is a broad element that contacts the eighth costals anteriorly along a long, anteriorly
concave suture and the second suprapygal posteriorly along a more or less straight suture
(poorly preserved). Laterally, the first suprapygal appears to contact only the eleventh
peripheral. The exact outline of the second suprapygal is uncertain, because most of its
sutures with surrounding elements are effaced. Posteriorly, just in front of the broken
margin of the carapace, the suture with the pygal is barely discernible.
Three cervical scales are clearly visible on the nuchal. Plesiochelyids have long been
thought to be characterized by this character, but its distribution is actually wider. For
example, several eurysternids are known to have three cervical scales (Bräm, 1965;Joyce,
2003;Anquetin & Joyce, in press). Scale sulci are clearly apparent on the carapace, but very
little can be said about the vertebral scales because a large part of the carapace is missing.
The first vertebral scale is a broad element, wider anteriorly than posteriorly. Its lateral
margins extends on the first costal and first peripheral, but not on the nuchal. Laterally,
the first vertebral scale reaches the lateral part of the first marginal. Nothing can be said
about the second and third vertebral scales. The fourth vertebral scale is a broad element
extending laterally about two-thirds of the length of the sixth and seventh costals. The
outline of the fourth vertebral scale is somewhat unusual. Posterolaterally, its lateral
margin extends abruptly onto the tenth peripheral. This unusual shape is symmetrical,
but, based on our experience of the intraspecific variability in plesiochelyids, we grant it
no systematic value. The fifth vertebral scale is a wide, pentagonal element extending
onto costals 8, suprapygals 1 and 2, and peripherals 10 and 11. There are four pleural
scales. The outlines of pleurals 1–3 are uncertain. The first pleural scale contacts
marginals 1–4 and maybe also the fifth marginal scale. The first pleural scale is slightly
shorter than pleurals 2 and 3. The second pleural scale reaches the seventh marginal scale
posteriorly on the sixth peripheral. The fourth pleural scale is a reduced element covering
only a small portion of the sixth and seventh costals and the medial part of the ninth and
tenth peripherals. Marginals are only partly preserved. Marginals 1–6 are still partly
visible on the right anterolateral part of the carapace. When preserved, the
pleuro-marginal sulci are always on the peripherals and never extend onto the costals. It
should also be noted that the last marginal scales (probably the twelfth pair, although it is
impossible to be sure) extend anteriorly onto the second suprapygal.
Plastron
The plastron of MAJ 2005-11-1 is mostly complete (Figs. 2D–2F and S3). The anterior
margin of the left epiplastron, the bridge area on the left hand side, and posterior tip of
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the xiphiplastra are broken. The matrix preserved the imprints of the broken parts of the
bridge and xiphiplastra. The total length of the plastron is 431 mm, measuring from the
epiplastra anteriorly to the imprint of the xiphiplastra posteriorly. As such, the plastron
represents 91.5% of the length of the preserved carapace (the true ratio would be slightly
lower if the pygal had been preserved). The plastron is strongly sutured to the carapace.
The bridge extends from the posterior part of the third peripheral to the anterior part of
the eighth. The axillary and inguinal notches are deep. A small central fontanelle is
present between the hyo- and hypoplastra. The anterior lobe is shorter than the posterior
lobe, which is itself shorter than the bridge measured between the axillary and inguinal
notches. The anterior lobe is trapezoidal in outline with a nearly straight anterior margin.
The posterior lobe has a triangular outline with a slightly rounded posterior tip (no anal
notch). The central part of the plastron is slightly concave. This concavity may have been
natural.
None of the two epiplastra is complete. The left one is missing its anterior margin,
whereas the lateral part of the right one is partly covered by matrix. As preserved, the
epiplastra are relatively short, wider than long elements. They contact one another
medially, the hyoplastra posteriorly, and the entoplastron posteromedially. The
epi-hyoplastron suture is straight and transverse. The entoplastron is a diamond-shaped,
slightly longer than wide element with its posterior faces slightly more elongated than the
anterior. The hyoplastron is a large, longer than wide element. Posteromedially, the
hyoplastron forms the anterior third of the central plastral fontanelle. The
hyo-hypoplastral suture is slightly concave anteriorly, more so medially. The hypoplastron
is shorter than the hyoplastron. It forms the remaining two-thirds of the central
fontanelle. The suture between the hypoplastron and the xiphiplastron is mostly straight
and transverse medially. Laterally, its bends suddenly backwards, as it is so often seen in
turtles. The xiphiplastron is a triangular, longer than wide element with a slight
broadening where the femoro-anal sulcus meets its lateral margin, as correctly noted by
Pictet & Humbert (1857). The midline contacts between the different plastral elements are
partly disarticulated (Fig. S3), so that the exact position of the sutures is difficult to assess.
Probably as a result, Pictet & Humbert (1857) erroneously described and depicted a very
small fontanelle between the hypo- and xiphiplastra. Direct examination of the specimen
and observation of the 3D surface reconstruction (Video S1 and Fig. S3) both suggest that
there is no such fontanelle in MAJ 2005-11-1.
Gular and extragular scales are relatively small. The gular scales extend only a little
onto the anteromedial part of the entoplastron. The extragular scales are restricted to the
epiplastra. The long humeral scales cover the rest of the anterior plastral lobe. The
pectoral scale is nearly as long as the abdominal scale on the midline, but both are shorter
than the humeral scale. The abdominal-femoral sulcus is oblique and extends from the
inguinal notch to the posterior third of the central plastral fontanelle. The femoral is the
longest scale of the plastron. The femoral-anal sulcus is deeply concave posteriorly in its
medial part. The anal scales are restricted to the xiphiplastra. The medial sulcus between
paired scales is unusually irregular. The median sulcus diverges strongly from the midline
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between the humeral and pectoral scales, being notably sinusoidal between the latter. The
median sulcus is more poorly preserved between the femoral and anal scales, but
observation of the 3D surface reconstruction (Video S1) suggests that it might also have
been slightly sinusoidal, at least in the posterior part of the femoral scales. The bridge area
is covered by four inframarginal scales increasing in length posteriorly. The two first and
the last are restricted to the hyoplastron and hypoplastron, respectively. The third
inframarginal scale covers the hyoplastron anteriorly, the hypoplastron posteriorly, and a
small portion of the fifth peripheral laterally.
DISCUSSION
Skull-shell associations
Despite a profusion of material collected from the Late Jurassic of Europe, relatively few
species are known from both skull and shell material. European lithographic limestone
localities (especially Solnhofen, Kelheim, and Cerin) have produced a fair number of
relatively complete, articulated specimens with shell, skull, and various elements of the
skeleton (e.g., von Meyer, 1860), but the cranial material is always badly crushed and very
difficult to interpret. Hence, the skull is ‘known’ in some eurysternids, such as
Eurysternum wagleri,Idiochelys fitzingeri, and Palaeomedusa testa (e.g., Jourdan, 1862;
Joyce, 2003;Anquetin & Joyce, in press), but only scarce information can be gathered from
these examples.
Among European Late Jurassic turtles, only Solnhofia parsonsi and Plesiochelys etalloni
are sufficiently known from both skull and shell material. Solnhofia parsonsi was
described by Gaffney (1975b) based on two isolated skulls, one from the Solnhofen region
(Germany), one from Solothurn (Switzerland). Later, Joyce (2000) described a nearly
complete skeleton that can be confidently referred to S. parsonsi. Additional skull and
associated fragmentary shell remains were described by Rieppel (1980) and assigned to
Thalassemys moseri Bräm (1965), but the validity of both this taxon and this referral was
questioned by subsequent authors (e.g., Gaffney & Meylan, 1988;Lapparent de Broin,
Lange-Badré & Dutrieux, 1996). This material should therefore be revised.
Skulls of P. etalloni are known since the early nineteenth century (e.g., Cuvier, 1824;
Rütimeyer, 1873;Bräm, 1965), although they were not necessarily assigned to this species
in those times. The Solothurn Turtle Limestone has produced four Plesiochelys skulls,
which Gaffney (1975a) identified as belonging to a single species. Among these four
skulls, only one (NMS 594) is associated with significant shell material (few disarticulated
costals and peripherals and partial posterior half of a plastron). Bräm (1965) identified
this specimen as P. etalloni based on the probable presence of a central plastral fontanelle.
However, this material is too fragmentary to allow a definitive specific identification.
Only one other skull-shell association exists for P. etalloni. It is a specimen (MH 435) that
was found in the Kimmeridgian near Glovelier (Canton of Jura, Switzerland). Bräm
(1965) referred this material to P. etalloni without further description and depicted the
skull and a humerus (ibid.: plate 4, Figs. 1–4). The skull, one of the best for P. etalloni, was
subsequently prepared and Gaffney (1975a) followed the identification of Bräm (1965).
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 10/17
Figure 3 Shell of specimen MH 435. MH 435, Plesiochelys etalloni (Pictet & Humbert, 1857). (A) pho-
tograph of the carapace; (B) interpretative drawing of the carapace; (C) photograph of the plastron; (D)
interpretative drawing of the plastron. Bones are white; stripped lines indicate internal bone layers; green
solid lines indicate scale sulci; dotted areas indicate reconstructed parts; matrix is gray. Abbreviations:
ab, abdominal; co, costal; eg, extragular; epi, epiplastron; ento, entoplastron; fem, femoral; gu, gular; hyo,
hyoplastron; hypo, hypoplastron; hum, humeral; n, neural; nu, nuchal; p, peripheral; pect, pectoral; pl;
pleural; v, vertebral.
Gaffney (1975a;7) examined the associated, incompletely prepared shell material and
concluded that ‘‘the shell features as determinable at this time are consistent with [his]
concept of Plesiochelys etalloni’’. Because Gaffney (1975a)’s concept of P. etalloni is
inclusive and not necessarily accepted among fossil turtle specialists, it was important to
reassess the shell material of MH 435 and compare it with the newly rediscovered
holotype specimen of P. etalloni.
If the skull of MH 435 has been extensively studied (Gaffney, 1975a,1976;Sterli, 2010;
Carabajal et al., 2013), the associated shell material has never been described or
illustrated. This material (Fig. 3) consists of the anterior half of a shell with carapace and
plastron still in articulation. Everything posterior to the fifth costal on the carapace and
inguinal notch on the plastron is missing. Both the carapace and the plastron are greatly
fractured. Many fragments of the costals are missing. The carapace is oval in outline with
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 11/17
a broad, shallow nuchal notch (Figs. 3A–3B). The nuchal is a wide and trapezoidal
element. The first neural is rectangular, whereas neurals 2–4 are hexagonal with their
shorter sides anteriorly. Cervical scale sulci are not preserved. The first vertebral scale is a
broad, trapezoidal element that extends laterally onto the first peripheral and contacts the
lateral border of the first marginal scale. The second and third vertebral scales are wide
and hexagonal. Their sulci are moderately sinuous, as it is common in Solothurn
specimens referred to P. etalloni (Bräm, 1965). The anterior margin of the anterior lobe of
the plastron is rounded (Figs. 3C–3D). The epiplastron is separated from the hyoplastron
by a straight, transverse suture. The hyoplastron is longer than wide. There is an oval
central fontanelle between the hyo- and hypoplastron. The hyo-hyoplastral suture is
relatively straight and slightly oblique defining a small concavity toward the anterior. The
bridge is long and osseous. It extends from the posterior half of the third peripheral to the
anterior part of the eighth peripheral. The scale arrangement on the plastron is similar to
that of MAJ 2005-11-1. The median sulcus between the humeral and pectoral scales
diverges strongly from the midline, although it is not sinusoidal as in the holotype of P.
etalloni. There are four inframarginal scales increasing in length posteriorly. The above
description indicates that the shell of MH 435 does not significantly differ from that of
MAJ 2005-11-1. Therefore, MH 435 can be confidently referred to P. etalloni (sensu this
study, not Gaffney, 1975a). This confirms the importance of this specimen, especially for
phylogenetic reconstructions.
Alpha taxonomy
As mentioned above, comparisons for the present study are restricted to the Plesiochelys
species described by Rütimeyer (1873) and later revised by Bräm (1965), i.e., forms first
described from the Late Jurassic of the Swiss and French Jura Mountains. Many
specimens from the Late Jurassic of France, Germany, England, Spain and Portugal have
afterwards been either referred to P. etalloni and P. solodurensis or assigned to new or
indeterminate species, but these need to be revised thoroughly. Kuhn (1964) listed 22
species of Plesiochelys typified based on European material. It is far beyond the scope of
the present study to revise the taxonomy of the genus Plesiochelys.
Another issue is the relatively inclusive synonymy list proposed by Gaffney (1975a),
who synonymized the following species with P. etalloni:Emys jaccardi,Stylemys
lindenensis,P. solodurensis,P. sanctaeverenae,Craspedochelys picteti, and C. crassa.
Stylemys lindenensis is a form from the Late Jurassic of Hanover, Germany, and, along
with many other specimens from the same region, it has never been properly revised
since Oertel (1924). All other species but E. jaccardi were described based on material
from Solothurn, Switzerland. Emys jaccardi was referred to Plesiochelys by Rütimeyer
(1873) and Bräm (1965). In contrast, Antunes, Becquart & de Broin (1988) and Lapparent
de Broin, Lange-Badré & Dutrieux (1996) referred this species to the genus Craspedochelys
Rütimeyer (1873), which they distinguished from Plesiochelys by a shell as wide as long
and a shortened plastron. Gaffney (1975a) argued that variation in shell shape, especially
relative width (as used to differentiate E. jaccardi and C. picteti from P. etalloni), was
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 12/17
probably the result of postmortem deformation and should not be considered for
systematic purposes. The objective of the present paper is not to settle this argument. The
fact is that Bräm (1965) is the last author to have thoroughly reassessed the shell
morphology of these forms. Gaffney (1975a) focused essentially on skull description and
did not describe shell morphology in detail. Lapparent de Broin, Lange-Badré & Dutrieux
(1996) studied some of the Solothurn material, but they did not clearly formalized their
views, instead proposing a general discussion as part of the description of new material
from France. For the purpose of the present paper, we restrict our comparisons to P.
solodurensis,P. sanctaeverenae and P. langii.
According to Rütimeyer (1873) and Bräm (1965), both P. etalloni and P. solodurensis are
present in Solothurn, the type locality of P. solodurensis. However, Bräm (1965) himself
admitted that differentiating the two species was not easy. Plesiochelys etalloni was
supposed to produce slightly larger individuals than P. solodurensis and to retain a small
central plastral fontanelle in the adults (Bräm, 1965). The proposed difference in size is
minor (about 10%) and is not interpreted as being significant. We have scrutinized all
fairly complete specimens from Solothurn referred to both P. etalloni and P. solodurensis,
representing about 30 individuals. We have extensively looked for additional characters
that would confirm the presence of two species (one with a central plastral fontanelle and
one without), but have found none. For example, a close comparison between MAJ
2005-11-1 (holotype of P. etalloni) and NMS 59 (lectotype of P. solodurensis) reveals only
little differences: the shape of the posterolateral sulcus of the fourth vertebral (probably
anomalous in MAJ 2005-11-1); the very minute extension of the fourth marginal onto
costal 2 in NMS 59; the central plastral fontanelle in MAJ 2005-11-1; and the extension of
the anal scale onto the hypoplastron in NMS 59. Anomalous scale shape is relatively
common among Solothurn turtles, especially for vertebral scales. Similarly, both the
extension of the fourth marginal onto costals and the extension of the anal scale onto the
hypoplastron, characters that are otherwise diagnostic for Xinjiangchelyidae (e.g., Tong
et al., 2012;Rabi et al., 2013;Pérez-García, Gasulla & Ortega, in press), are variable in P.
etalloni and other plesiochelyids (e.g., Pérez-García, in press). Hence, the retention of a
central plastral fontanelle in adults is interpreted as an intraspecific variation of P. etalloni,
and P. solodurensis is considered a subjective junior synonym of this species.
Bräm (1965) found no significant difference between NMS 123 and NMS 126, two
carapaces referred to P. langii, and NMS 59, and therefore synonymized P. langii with P.
solodurensis. We agree and similarly find no significant difference between these
specimens and MAJ 2005-11-1. Consequently, P. langii is synonymized with P. etalloni.
Plesiochelys sanctaeverenae was defined by Rütimeyer (1873) mainly based on NMS 118, a
large, incomplete carapace. Bräm (1965) designated this specimen as the lectotype and
considered this species as valid based on its larger size (carapace length =565 mm) and
elongate outline. However, observable characteristics do not allow to differentiate NMS
118 from others specimens we refer here to P. etalloni, especially neither from MAJ
2005-11-1 nor NMS 59. Concerning the outline of this specimen, Bräm (1965) was
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 13/17
probably misled by the fact that the lateral parts of the carapace are largely missing.
Consequently, P. sanctaeverenae is also considered a subjective synonym of P. etalloni.
From the above, we recognize only one species of Plesiochelys in the Jura Mountains:
Plesiochelys etalloni. Although this conclusion may appear superficially similar to that of
Gaffney (1975a), we reached it through an extensive re-evaluation of the Solothurn
material and a redescription of the type material of P. etalloni, which was unavailable for
these past 150 years. Since Gaffney (1975a),Gaffney (1976), we have an excellent
knowledge of the cranial morphology of P. etalloni. Thanks to the present study, we now
have a better understanding of the shell morphology and intraspecific variability of this
species.
ACKNOWLEDGEMENTS
The Lacroix family is warmly thanked for the donation of this specimen to the MAJ. We
thank Silvan Thüring (NMS) and Loïc Costeur (MH) for providing access to specimens in
their care. The 3D surface scanning of MAJ 2005-11-1 was realized by Vincent Lacombe
(DiGiScan3D). The high quality 3D surface reconstructions presented in Figs. S2 and S3
were produced by David Vuillermoz (MAJ). Thanks are extended to Christian Püntener
for sharing his considerations on Plesiochelys, as well as Thierry Malvesy (Muséum
Cuvier, Montbéliard, France) and Pascal Leblanc (Muséum d’histoire naturelle, Besançon,
France) for their assistance during an earlier phase of this study. Comments from Andrew
Farke, Walter Joyce and Adán Pérez-García greatly improved the manuscript.
ADDITIONAL INFORMATION AND DECLARATIONS
Funding
JA’s visits to NMS and MH were funded as part of a postdoctoral grant from the Simone
and Cino del Duca Foundation (2008 Foundation Prize awarded to Philippe Janvier,
MNHN, Paris). The funders had no role in study design, data collection and analysis,
decision to publish, or preparation of the manuscript.
Grant Disclosures
The following grant information was disclosed by the authors:
Simone and Cino del Duca Foundation (2008 Foundation Prize awarded to Philippe
Janvier, MNHN, Paris).
Competing Interests
The authors declare that they have no competing interests.
Author Contributions
•Jérémy Anquetin, Sylvie Deschamps and Julien Claude analyzed the data, wrote the
paper.
Supplemental Information
Supplemental information for this article can be found online at
http://dx.doi.org/10.7717/peerj.258.
Anquetin et al. (2014), PeerJ, 10.7717/peerj.258 14/17
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