Cearachelys, a New Side-Necked Turtle (Pelomedusoides: Bothremydidae) from the Early Cretaceous of Brazil

20 Pages·2001·0.56 MB·English

by  Eugene S. Gaffney

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number3319,20pp.,9figures,1table February 27,2001
Cearachelys, a New Side-Necked Turtle
(Pelomedusoides: Bothremydidae) from the Early
Cretaceous of Brazil
EUGENE S. GAFFNEY,1 DIOGENES DE ALMEIDA CAMPOS,2 AND
REN HIRAYAMA3
ABSTRACT
The early Cretaceous Santana Formation exposed on the Chapada do Araripe in Ceara´ State,
northeastern Brazil, hasyielded remains of a side-necked turtle,Cearachelysplacidoi,newgenus
andspecies.Cearachelysisbasedontwoskeletons,eachconsistingofarticulatedshell,associated
skull,andpostcraniainvaryingdegreesofcompleteness.Cearachelysisapelomedusoidpleurodire
belonging to the family Bothremydidae Baur, 1891, based on these bothremydid characters: (1)
precolumellar fossa absent, (2) occipital condyle consisting only of exoccipitals, (3) foramen sta-
pedio-temporaleanteriorlyfacing,and(4)exoccipitalcontactsquadrate.WithintheBothremydidae,
Cearachelys is best resolved as the sister group of Bothremys, Rosasia, Foxemys, Zolhafah, and
Polysternon. Cearachelys differs from the other two pleurodires in the Santana Formation in the
bothremydidcharacterslistedaboveandinhavingaquadrate-basioccipitalcontact,aprooticcom-
pletely covered in ventral view, and a high lingual ridge on the lower jaw.
INTRODUCTION thought to consist of more than a dozen
First recognized as a group of extinct skull-based genera, more than half still un-
side-necked turtles in 1891 by George Baur described. The purpose of this paper is to
on the basis of the skull of Bothremys cooki name and describe a new bothremydid that
Leidy, 1865, the Bothremydidae is now is represented by two nearly complete skel-
1Curator,Divisionof Paleontology,AmericanMuseumofNaturalHistory.
2Departamento Nacional da Produc¸ao Mineral, Divisao de Minerac¸ao, Av. Pasteur 404, Rio de Janeiro 22290–
240, Brazil.
3TeikyoHeiseiUniversity,2289 Uruido,Ichihara,Chiba 290–01,Japan.
2 AMERICAN MUSEUM NOVITATES NO. 3319
etons. It is one of the oldest members of the and Nigeremys (Bergounioux and Crouzel,
family. 1968;LapparentdeBroinandWerner,1998).
The Bothremydidae extend from the early Other pelomedusoid skulls are Araripemys
Cretaceous to the Miocene and are found on (Meylan, 1996), Hamadachelys (Tong and
all the continents except AntarcticaandAus- Buffetaut, 1996), and an unnamed Santana
tralia.Adultbothremydidsrangeinsizefrom genus (represented by FR 4922, Gaffneyand
less than 25 cm to more than 150 cm in Meylan, 1991). A general treatment and de-
length. Throughout their record, bothremy- scription of pleurodire skulls, turtle-skull
dids occur as fossils in near-shore marine morphologyandterminology,andaliterature
sediments as well as terrestrial freshwater review is in Gaffney (1979).
units. Bothremydid cranial diversity also We use Lapparent de Broin and Werner’s
suggests a reinterpretation of pleurodire his- (1998) reference to a Bothremys Group and
tory. This family was a widespread,relative- a Nigeremys Group (which includes Taph-
ly diverse group adapted to many habitats, rosphys in our usage), as these continue to
rather than a conservative group occupying form monophyletic taxa in most of our cur-
a few restricted niches. The original miscon- rent analyses. Our contents of these groups
ception arose from the fact that the more are as follows: Bothremys Group—Bothre-
commonly preserved shells are unusually mys,Rosasia,Zolhafah,Foxemys;Nigeremys
conservative in pelomedusoids when com- Group—Nigeremys, Arenila, and Taphros-
pared with the skull; the diversity of this phys.
group has gone unappreciated. TheSantanaFormationismostfamousfor
Although the Bothremydidae was named its early Cretaceous fishes (Maisey 1991),
as early as 1891 by George Baur, the term but it also has a very important turtle fauna
fell into disuse for most of this century, and consisting of the following:
thefewincludedtaxa,particularlyBothremys
Cryptodira
and Taphrosphys, were simply included in
Protostegidae
the Pelomedusidae. Broin in Antunes and Santanachelys gaffneyi (Hirayama, 1998)
Broin(1988)andBroin(1988)revivedBoth-
Pleurodira
remydidae, provided a new diagnosis, and
Araripemydidae
added taxa, such as Rosasia, based on skulls
Araripemys barretoi (Meylan, 1996)
and shells. Recent papers on fossil pleuro-
Unnamed family
dires, such as Meylan (1996), Lapparent de
Unnamed genus, FR 4922 (Gaffney and
Broin and Werner (1998), and Tong et al.
Meylan, 1991)
(1998), use the Antunes and Broin (1988)
terminology, in which Bothremydidae, Po- Bothremydidae
Cearachelysplacidoi(newgenusandspecies
docnemididae,andPelomedusidae(restricted
described here)
to Pelusios and Pelomedusa) are contained
in the Pelomedusoides (which equals Pelo-
medusidae in the classic sense). Bothremy- Institutional Abbreviations
dids are now recognized as a far more wide-
MPSC Museu Paleontolgico de Santana do
spread and diverse group than previously
Cariri, Ceara´ State, Brazil
considered.
TUTg Teikyo Heisei University, Chiba,Japan
Useful reviews of the literature on both-
FR Forschungsinstitut Senckenburg, Frank-
remydids can be found in Broin (1988) and
furt, Germany
Antunes and Broin (1988). Information in YPM Yale Peabody Museum, New Haven,
varying degrees of completeness on previ- CT, USA
ously described bothremydid skulls are as USNM UnitedStatesNationalMuseum,Wash-
follows: Bothremys (Gaffney and Zangerl, ington DC, USA
1968; Gaffney, 1977), Taphrosphys (Gaff-
ney, 1975), Rosasia (Antunes and Broin, Anatomical Abbreviations
1988),Foxemys(Tongetal.,1998),Zolhafah
(Lapparent de Broin and Werner, 1998), Ar- bo basioccipital
enila(LapparentdeBroinandWerner,1998), bs basisphenoid
2001 GAFFNEY ET AL.: CEARACHELYS 3
ex exoccipital present as in Bothremys, Rosasia, and Foxe-
fpcci foramen posterius canalis carotici interni mys; condylus occipitalis formed only by ex-
fr frontal occipitals as in Zolhafah; foramen stapedio-
ju jugal
temporale facing anteriorly.
mx maxilla
Carapace moderately domed as in Pelome-
na nasal
dusa, oval in outline, with eight neurals com-
op opisthotic
pletely separating all eight costals in contrast
pa parietal
pal palatine to at least one pair of costals meeting in mid-
pf prefrontal line as in most other bothremydids; second
pm premaxilla neural does not contact first costals. Plastron
po postorbital withanteriorloberoundedandbroaderthanin
pr prootic other Santana pelomedusoids; pectoral scales
pt pterygoid do not extend anteriorly onto entoplastron,but
qj quadratojugal
do extend posteriorly onto mesoplastra; me-
qu quadrate
soplastron small and laterally placed as inPo-
so supraoccipital
docnemis.
sq squamosal
vo vomer
Cearachelys placidoi, new species
SYSTEMATICS TYPE SPECIMEN: MPSC (figs. 2, 3, 6, 7), a
partial skull, shell, cervicals, and limb ele-
ORDERTESTUDINESLINNAEUS,1758
ments.
MEGAORDERPLEURODIRACOPE,1864(FIDE TYPELOCALITY:ProbablySantanadoCariri,
GAFFNEYANDMEYLAN,1988)
Ceara´, Brazil.
HYPERFAMILYPELOMEDUSOIDESCOPE,1868 HORIZON:(?)RomualdoMemberoftheSan-
FAMILYBOTHREMYDIDAEBAUR,1891 tana Formation, probably Albian in age (ca.
110 mya; Maisey, 1990, 1991).
Cearachelys, new genus
DIAGNOSIS: Same as for genus.
TYPE SPECIES: Cearachelys placidoi, new ETYMOLOGY: In honor of Dr. Placido Nu-
genus and new species. vens, DirectoroftheMuseuPaleontologicode
DISTRIBUTION: Aptian or Albian (early Cre- Santana do Cariri, Ceara´, Brazil; and chelys,
taceous) of Brazil. turtle.
ETYMOLOGY: In allusion to the type locality REFERRED MATERIAL: TUTg 1798—Nearly
thatisinCeara´ State,Brazil;andchelys,turtle. complete skeleton with skull, lower jaw,shell,
cervicals, and limb elements (figs. 4, 5, 8, 9),
DIAGNOSIS near Santana do Cariri, Romualdo Member,
SantanaFormation.PurchasedfromvonLeon-
Skull triangular, orbitsdorsolaterallyplaced,
hardt, 1993.
not dorsally as in Bothremysand Foxemys;ju-
gal separated from orbital margin in contrast
tomostbothremydids;jugalenteringtriturating DESCRIPTION
surface, but not to the extent seen in Bothre-
PREFRONTAL
mys;trituratingsurfacestriangularandexpand-
ed posteriorly, but not to the extent seen in The prefrontal is preserved on both sidesof
Bothremys and Foxemys; triturating surfaces TUTg 1798. It is similar to that bone in living
smooth, no pits as in Bothremys and Rosasia; Pelomedusidae, but differs from species such
broad maxilla-quadratojugal contact; antrum asPelomedusasubrufainprojectinganteriorly
postoticum moderate as in Podocnemis, not to a greater extent, so that the dorsal margin
smallasinBothremys;eustachiantubeandsta- oftheaperturanariumexternaismoreanterior
pes not separated by bone in incisura colu- than the ventral margin. The prefrontal in
mellae auris; quadrate-basioccipital contact Cearachelysisdorsallyconvex,ratherthanflat
present; foramen posterius canalis carotici in- as in some Pelomedusidae. The resultantmor-
terni formed by basisphenoidandpterygoidas phology gives Cearachelys a prominent and
in Rosasia; supraoccipital-quadrate contact projecting preorbital aspect comparable to
4 AMERICAN MUSEUM NOVITATES NO. 3319
Fig.1. Cearachelysplacidoi,n.gen.&sp.,SantanaFormation,earlyCretaceous,Ceara´State,Brazil.
Restoration ofskullbased on MPSCspecimen andTUTg1798.Dorsal(left),ventral(right),andlateral
(center) views.
some Pelomedusidae, such as Pelusios subni- FRONTAL
ger.
The prefrontal in Cearachelys has the usual The frontal of Cearachelys is preserved on
pelomedusoidcontacts:maxillaanterolaterally, both sides in TUTg 1798. It is similar in size,
frontal posteriorly. It borders theorbitlaterally shape, and contacts to living Pelomedusidae.
andtheaperturanariumexternaanteriorly.The Thefrontalcontactsarewiththeprefrontalan-
ventralsurfaceoftheprefrontalinCearachelys teriorly, orbit laterally, postorbital posterolat-
issmooth,concaveventrallyinitsanteriorpor- erally,parietalposteriorly,andtheotherfrontal
tion, but bears the parasagittal ridge for the medially. Anteriorly thefrontalprojectsonthe
sulcus olfactorius more posteriorly. The pre- midline to a considerable extent on theventral
frontal sends a process ventrally along the an- surface,butonlyslightlyonthedorsalsurface.
terior margin of the fossa orbitaliscomparable The frontalformsthewell-developedsulcus
in size and extent to that in Recent Pelome- olfactorius on the ventral surface. In Cearach-
dusidae. It contacts the maxilla for most of its elys the sulcus is very similar tothelivingPe-
length and does not reach other elements. lomedusidae. The frontal in Cearachelys does
2001 GAFFNEY ET AL.: CEARACHELYS 5
not have a ventral process along the edge of In Cearachelys a very narrow process of the
the processus inferior parietalis, although the postorbitalrunsventrallyalongtheorbitalmar-
frontal does reach the processus as in recent gin to reach or nearly reach the maxilla and
Pelomedusidae. prevent jugal exposure. On the left side of the
MPSC specimen there issomebreakagealong
PARIETAL the orbital margin in this area, but it is clear
that the postorbital contacts the maxilla in a
The parietal is preserved on both sides in
narrowareaofsuturalinterdigitation.InTUTg
TUTg1798andtheMPSCspecimen,although
1798bothsidesshowthecontact.InLapparent
it is not entirely complete in either skull. The
deBroinandWerner(1998)anunnamedMor-
parietal of Cearachelys is nonetheless com-
occan skull is figured, which shows a broad
pletely known through both specimens.
contact of postorbital and maxilla, and this
The dorsal plate of the parietal in Cearach-
condition is similar to Cearachelys. No other
elys contacts the frontal anteriorly and is ex-
bothremydid shows this retraction of the jugal
cluded from the orbit as in other Bothremy-
from the orbit. Ventrally thejugalofCearach-
didaeandthePelomedusidae.Laterallythepa-
elys is exposed on the palate to a limited ex-
rietalcontactsthepostorbital,butnotthequad-
tent, not to as great an extent as seen in Both-
ratojugal, as in FR 4922. The temporal
remys and Rosasia.
emarginationinCearachelysismoreextensive
The jugal is exposed in the floor and pos-
than in living Podocnemididae and Foxemys,
terior wall of the orbit in Cearachelys as in
but not as extensive as in Pelomedusidae.The
most pelomedusoids. In the orbital floor the
otic chamber is completely uncovered, but
jugal contacts the postorbitaldorsallyandpos-
there is a relatively long suture between the
teriorly, the maxilla laterally and anteriorly,
parietalandthepostorbitalrelativetothatseen
and the palatine medially. The limited postor-
in the Pelomedusidae.
bital-maxilla contact barely separates the or-
The ventral process of the parietal, the pro-
bitalfloorexposureofthejugalfromthecheek
cessus inferior parietalis, is well preserved in
exposure of the jugal, a condition unique to
both skulls. It has relations similar to those in
Cearachelys. The postorbital wall of Ceara-
Pelomedusidae. Anteriorly it contacts the pter-
chelys shows the jugal forming the more ven-
ygoid and forms most of the side wall of the
tral portion, contacting the maxilla ventrolat-
braincase.Posteriorlytheparietalformsthean-
erally, the quadratojugal laterally, the postor-
terodorsalmarginoftheforamennervitrigem-
bital dorsally, and the pterygoid posteromedi-
ini (the ventral margin is formed by the pter-
ally.
ygoidandtheposterodorsalmarginbythepro-
otic). Posterior to the foramen nervi trigemini,
the parietal contacts the prootic and then the QUADRATOJUGAL
supraoccipital in a suture that rises dorsally to
The quadratojugal is preserved on the left
the skull roof.
side of the MPSC specimen and on both sides
of TUTg 1798.
JUGAL ThequadratojugalofCearachelysformsthe
Thejugalispreservedcompletelyontheleft posterior part of the cheek. There is only a
side and in part on the right sideoftheMPSC slight dorsal curve to the lower margin of the
specimen.InTUTg1798theleftjugaliscom- quadratojugaltosuggestacheekemargination;
plete, but only part of the right jugal is pre- nothing like the emargination seen in Pelo-
served. medusidae is present. The quadratojugal of
The jugal is a complex element that can be Cearachelys extends from the anterior limitof
describedashavingthreeareas:lateral,ventral, the upper temporal emarginationtotheventral
and posterior (with two exposure surfaces,an- margin of the cheek. In contrast to members
terior and posterior). The lateral exposure of of the Pelomedusidae, which have a well-de-
the jugal in Cearachelys is unusual among velopedcheekemarginationandnojugal-max-
bothremydids. The jugal lies just posterior to illa contact, Cearachelys has a broad maxilla-
the orbit as in all bothremydids; however, in quadratojugal contact, as in Foxemys, Nigere-
most bothremydids the jugal enters the orbit. mys,Polysternon,anunnamedMoroccanform
6 AMERICAN MUSEUM NOVITATES NO. 3319
Fig.2. Cearachelysplacidoi,n.gen.&sp.,MPSCspecimen,holotype,SantanaFormation,Santana
do Cariri, Brazil. A, dorsal; B, ventral; C, right lateral; D, anterior; E, left lateral; F, posterior. See fig.
3 for key.
(Lapparent de Broin and Werner, 1998), and curved contact with the quadrate. Posterodor-
Rosasia. It is likely that this is a Bothremydi- sally a very narrow process of the quadrato-
dae synapomorphy. jugal contacts the squamosal.
In Cearachelys the anterior contacts of the
quadratojugal are with the maxilla anteroven- SQUAMOSAL
trally, the jugal anterodorsally, and the post- The squamosal is preserved in both Cear-
orbital dorsally. Posteriorly there is a long achelys specimens.
2001 GAFFNEY ET AL.: CEARACHELYS 7
Fig. 3. Key to fig. 2.
The squamosal is a cone-shaped bone that antrum that is quite large. Cearachelys has an
sitsontheposterodorsalcornerofthequadrate antrum postoticum intermediate in size be-
and contains much of the antrum postoticum. tween these, comparable to that in Foxemys.
The antrum of Cearachelysismoderatelywell The complete squamosalisnotknownfor
developed relative to other pelomedusoids. other bothremydids, such as Arenila, Zol-
Bothremys and Taphrosphys have an antrum hafah, Rosasia, or Bothremys. But in Fox-
that is very small, merely an elongate canal, emys the posterior part of the squamosal is
while members of the Pelomedusidae have an developed into a flat plate. In Taphrosphys
8 AMERICAN MUSEUM NOVITATES NO. 3319
Fig. 4. Cearachelys placidoi, n. gen. & sp., TUTg 1798, Santana Formation, Santana do Cariri,
Brazil. A, dorsal; B, ventral; C, right lateral; D, anterior; E, left lateral; F, posterior. See fig. 5 for
key.
there is a more vertical flange extending POSTORBITAL
ventrally. Cearachelys lacks these posterior
processes and ends in a curved edge with Both postorbitals are preserved in TUTg
only a slight horizontal component contin- 1798, but there is some damage and sutures
uous with the posterior extension of the op- are not entirely clear. However, by using in-
isthotic. It is similar to the condition in Pe- formation from both sides, the postorbital in
lomedusidae. this specimen can be fully restored. The
2001 GAFFNEY ET AL.: CEARACHELYS 9
Fig. 5. Key to fig. 4.
MPSC specimen has only the left postorbital Anteroventrally the postorbital contacts the
and that is missing part of its anterior edge. jugal, and posteroventrally it contacts the
The postorbital in Cearachelys is a long quadratojugal. Anteromedially the postorbit-
element extending from the orbit to the tem- al contacts the frontal, and posteromedially
poralskullroofmargin,muchasinFoxemys. the parietal.
The postorbital of Cearachelys is larger than
in Araripemys, Pelomedusidae, and Podoc-
PREMAXILLA
nemididae. A very narrow ventral processof
the postorbital in Cearachelys contacts the Both premaxillae are present, but dam-
maxilla in the orbital margin, barely pre- aged, in TUTg 1798. They are absent in the
venting jugal exposure in the orbital margin. MPSC specimen.
10 AMERICAN MUSEUM NOVITATES NO. 3319
Fig. 7. Cearachelys placidoi, n. gen. & sp.,
MPSC specimen, holotype, shell in ventral view.
surface, the premaxilla rises in a shallow,
smooth arch to the vomer contact. In Foxe-
mys, Bothremys, Zolhafah, and Polysternon
there is a step on the triturating surface be-
tween the labial ridge and vomer. The pre-
maxilla of Cearachelys is triangular, being
broadest anteriorly and narrowing posterior-
ly. The lateral limits, however, are represent-
ed by broken edges and the precise position
of sutures is not clear.
The dorsal surfaceofthepremaxillaforms
the anterior floor of the fossa nasalis and the
marginoftheaperturanariumexterna.Ason
the ventral surface, the dorsal surface slopes
posterodorsally to meet the vomer. The ap-
ertura ventral margin is nearly straight in
Cearachelys, with only a slight dorsal curve
Fig. 6. Cearachelys placidoi, n. gen. & sp., on the midline, similar to Foxemys but in
MPSC specimen, holotype, shell in ventral (up- contrasttotheaperturamargininBothremys,
per) and dorsal (lower) views. (See fig. 7). which has a sharp dorsal curve at the mid-
line.Nuancesofshapeoftheaperturanarium
externa, however, are variable even among
ThepremaxillaofCearachelysbearsadis-
species of living Pelusios.
tinct labial ridge anteriorly with a flat plate
posteriorly. The labial ridge, however, is rel-
MAXILLA
atively thin in Cearachelys in anterior view,
in contrast to the deeper ridge of Foxemys. The posterior portion of the left maxilla is
Posterior to the labial ridge on the palatal preserved in the MPSC specimen. Most of