Redescription of the skull of Dacquemys Williams, 1954, a podocnemidid side-necked turtle from the late Eocene of Egypt

16 Pages·2002·2.4 MB·English

by  Gaffney, Eugene S.

AMERICAN MUSEUM
Novitates
PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3372, 16 pp., 5 figures, 2 tables June 21, 2002
Redescription of the Skull of Dacquemys
Williams, 1954, a Podocnemidid Side-Necked
Turtle from the Late Eocene of Egypt
EUGENE S. GAFFNEY,’ DONALD D. DEBLIEUX,”? ELWYN L. SIMONS,?
MARCELO R. SANCHEZ-VILLAGRA,* AND PETER A. MEYLAN>
ABSTRACT
The known material of the side-necked turtle Dacquemys paleomorpha Williams, 1954,
consists of the type skull and a new skull from the late Eocene of Egypt. Dacquemys is
reaffirmed as a member of the Podocnemididae because of its well-developed cavum ptery-
goideus. Within the Podocnemididae Dacquemys uniquely possesses a fully roofed temporal
region produced by a posteriorly extensive parietal and wide supraoccipital, a very wide in-
terorbital area, and two accessory maxillary ridges meeting anteriorly to form an enclosed
trough.
INTRODUCTION species Stereogenys libyca Andrews, 1906.
In 1954, Williams recognized that this attri-
The type skull of the taxon redescribed — bution was inconsistent with the type skull
here was first described by E. Dacqué in material of Stereogenys cromeri Andrews,
1912 and referred by him, doubtfully and for 1901, the type of the genus, and that the
reasons that are unclear, to the shell-based Dacqué skull was distinct from all other
' Curator, Division of Paleontology, American Museum of Natural History. e-mail: [email protected]
? Duke University Primate Center, Durham, NC 27705. Present address: Utah Geological Survey, Salt Lake City,
UT 84114.
3 James B. Duke Professor of Anthropology, Department of Biological Anthropology and Anatomy, and Primate
Center, Duke University, Durham, NC 27705.
4 Universitat Tiibingen, Zoologisches Institut, D-72076, Germany. e-mail: marcelo.@s unai-ntucebhingeenz.d e
> Eckerd College, St. Petersburg, FL 33733. e-mail: [email protected]
Copyright © American Museum of Natural History 2002 ISSN 0003-0082
2: AMERICAN MUSEUM NOVITATES NO. 3372
known Pleurodira. Williams named the form the classic sense). A useful compilation of
Dacquemys paleomorpha and provided a the pelomedusoid literature is found in Broin
brief description. Since 1954 there have been (1988) and in Lapparent de Broin (2000).
no further contributions to the understanding The only computer-generated cladogram of
of this genus. It is the purpose of this paper Podocnemididae available at present is Mey-
to describe the type skull, following repre- lan (1996), which shows the relationships of
paration and cleaning, and to describe a new these families and the included genera.
skull discovered by the Duke University Pri-
mate Lab during ongoing fieldwork in Egypt. Institutional Abbreviations
Despite many field seasons of paleontologi-
cal work in Egypt by a number of institu- AMNH~ American Museum of Natural History
tions, only these two skulls of Dacquemys DPC Duke Primate Center, Duke University,
have come to light. The new skull preserves North Carolina
SMNS Staatliches Museum fiir Naturkunde,
a number of areas unavailable in the type,
Stuttgart
and together they allow a complete recon-
struction of the skull. This paper limits de-
Anatomical Abbreviations
scription to comparisons with the well-
known forms, the living podocnemidids Po-
bo basioccipital
docnemis, Erymnochelys, and Peltocephalus.
bs basisphenoid
It is worth examining the basis for
ex exoccipital
Dacqué’s original assignment of the type fr frontal
skull to Stereogenys libyca, primarily to see ju jugal
why he associated a shell with the skull. In mx maxilla
Dacqué (1912: 337) we translate his argu- op opisthotic
ment as follows: ‘““The reasons why we as- pa parietal
pal palatine
sign the skull to Stereogenys libyca Andrews
pf prefrontal
are the following: 1) because it is particularly
pm premaxilla
similar to Podocnemis but it cannot belong
po postorbital
to this species, 2) because [the skull] is rather
pr prootic
convex so it was not retractable, a condition pt pterygoid
which is consistent with the epiplastral tu- qj quadratojugal
bercles [gular projections] of Stereogenys li- qu quadrate
byca, 3) it is consistent with the size of the SO supraoccipital
shell [of Stereogenys libyca], 4) [both shell sq squamosal
and skull] are found in the same stratigraphic
level’’. It does not seem that any shells were SYSTEMATICS
associated in site with the original skull. He
was probably wrong about gular projections ORDER TESTUDINES LINNAEUS, 1758
preventing head retraction; living tortoises
MEGAORDER PLEURODIRA COPE, 1864 (FIDE
have projections and retract with no problem.
GAFFNEY AND MEYLAN, 1988)
Therefore, as Williams (1954) implied, there
is no shell associated with the type skull of HYPERFAMILY PELOMEDUSOIDES COPE, 1868a
Dacquemys paleomorpha.
FAMILY PODOCNEMIDIDAE
We use the terminology for pleurodires
COPE, 1868b
previously developed in Broin (1988), An-
Dacquemys Williams, 1954
tunes and Broin (1988), and more recently in
Meylan (1996), Lapparent de Broin and Wer- TYPE SPECIES: Dacquemys paleomorpha
ner (1998), Tong et al. (1998), and Gaffney Williams, 1954.
et al. (200la, 2001b, 2001c). This usage DISTRIBUTION: Late Eocene of Egypt.
places the families Bothremydidae, Podoc- DIAGNOSIS: A genus of podocnemidid
nemididae, and Pelomedusidae (restricted to pleurodire known only from the skull; char-
Pelusios and Pelomedusa) in the Pelomedu- acterized by the unique possession of a fully
soides (which equals the Pelomedusidae in roofed temporal region with a posteriorly ex-
2002 GAFFNEY ET AL.: DACQUEMYS 3
tensive parietal and wide supraoccipital com- the Staatliches Musuem ftir Naturkunde,
pletely covering the otic chamber in dorsal Stuttgart, was presumably part of a collection
view; broad parietal-squamosal contact not obtained from German geologist and private
seen in other podocnemidids; prefrontal ex- collector Richard Markgraf who lived in
tends to anterior margin of apertura narium Egypt and made extensive collections in the
externa as in Peltocephalus but in contrast to Fayum region during the early 20th century.
Podocnemis, interorbital distance very wide During this early period of collecting in the
with orbits facing laterally in contrast to liv- Fayum, locality information was typically
ing Podocnemididae; maxillae meet broadly vague and lacked attention to precise strati-
behind premaxillae; premaxillae recessed graphic level (Simons, 1968; Simons and
and not visible laterally in contrast to all oth- Rasmussen, 1990). The locality given in
er Pelomedusoides; vomer absent; anterior Dacqué (1912) first in reference to the shell
part of triturating surface more extensive and then the skull is “‘Unteroligocane Flu-
than in living Podocnemididae but secondary viomarinestuffe n6érdlich der Birket Qarun;
palate as seen in Shweboemys group absent; nordlich non Tamieh; ostlich vom Schwein-
two accessory maxillary ridges meet anteri- forthplateau. Schadal: aus derselben stufe bei
orly to form enclosed trough unique to this Diméh. Alles Fayum”’ (Dacqué 1912: 310),
genus; antrum postoticum small as in Podoc- which we translate as “‘Early Oligocene flu-
nemis; precolumellar fossa shallow as in Po- viomarine sediment north of Birket Qarun;
docnemis expansa; pterygoid-jugal contact north of Tamieh; east of the Schweinfurth
absent. Plateau. Skull from the same level near Di-
méh. All specimens being from the Fayum
Dacquemys paleomorpha Williams, 1954 area’’. The beginning of this entry is similar
to that typically given for fossils found in the
TYPE SPECIMEN: SMNS 12645, a nearly Jebel Qatrani Formation during this period,
complete skull without lower jaws (figs. 2 which are “‘north of Birket Qarun”’ or ‘“‘flu-
and 3), lacking parts of the left side and the viomarine series north of Birket Qarun”’ (Si-
central basicranial region (Dacqué, 1912: pl. mons, 1968). Birket Qarun is the name of the
II, figs. 6-8; Gaffney, 1979: fig. 128; Wil- large lake in the north of the Fayum depres-
liams, 1954: pl. 1). Measurements in table 1. sion. The reference to early Oligocene is also
TYPE LOCALITY AND HORIZON: Dacqué consistent with the Jebel Qatrani Formation,
(1912) gave the locality at first in reference which was thought to be late Eocene by the
to a shell: “‘Unteroligocéne Fluviomarines- earliest workers (1.e., Beadnell, 1905; An-
tuffe nordlich der Birket Qerun; nordlich non drews, 1906) but by the time of Dacqué’s
Tamieh; ostlich vom Schweinforthplateau. study was interpreted to be early Oligocene
Schadel: aus derselben stufe bei Diméh. Al- (Stromer, 1907; Osborn, 1908), with the un-
les Fayum”’ (Dacqué, 1912: 310). Williams derlying Qasr el Sagha Formation considered
(1954; repeated in Gaffney, 1979) has the lo- to be late Eocene. The reference to the skull
cality as “‘Diieh’’, which seems to be a mis- ‘“‘from the same sediments near Diméh”’ is
spelling of ““Diméh’’. The reference to the more difficult to interpret. Diméh refers to
skull “‘from the same sediment near Diméh’’ the ruins of a Greco-Roman temple and set-
presumably means the Qasr el Sagha or Bir- tlement located on the north shore of Birket
ket Qarun formations of late Eocene age. Qarun. It is possible that this reference in-
REFERRED MATERIAL: DPC 5986, partial dicates information given by the collector to
skull lacking anterior part of palate and some more accurately place the locality of this
of left side (figs. 4 and 5). Field no. 86—292, specimen, or it may be a general reference to
collected by Alex van Nievelt. Measure- the region north of Birket Qarun. The sedi-
ments in table 1. ments surrounding Diméh include those of
LOCALITY AND HoRIZON: B-4 Uower Jebel the Umm Rigl Member of the Qasr el Sagha
Qatrani, %4 mile southeast of A). AMNH Formation (Gingerich, 1992) and of the un-
quarry B area, Eocene (Gagnon, 1997: fig. 1; derlying Birket Qarun Formation, both cov-
Kappelman et al., 1992). ered in part by Pleistocene and Holocene
DISCUSSION: The type specimen, housed in lake deposits from the once more extensive
AMERICAN MUSEUM NOVITATES NO. 3372
B
Fig. 1. Dacquemys paleomorpha, late Eocene, Fayum, Egypt, restorations based on SMNS 12645
and DPC 5986. A, Dorsal; B, ventral; C, lateral. Dotted lines indicate scale margins.
Birket Qarun (Bown and Kraus, 1988). The “east of Schweinfurth Plateau’’ may indicate
age and nature of the contact between these these lower sediments. We are not aware of
formations in the area around Diméh are the location of this plateau but the Qasr el
presently being investigated, but both marine Sagha temple was known as Schweinfurth’s
and continental vertebrate remains are found Temple, so it may be that his “‘plateau’’ is
in these sediments. This, along with the fau- located near the temple. Schweinfurth is
nal continuity that is a general feature of the known to have worked primarily in the area
Fayum sequence (Rasmussen et al., 1992), around Birket Qarun. At present, the Qasr el
makes it entirely possible that the type spec- Sagha Formation is generally thought to be
imen of Dacquemys was collected from ei- late Eocene (Priabonian) in age (Bown and
ther the Qasr el Sagha or Birket Qarun for- Kraus, 1988; Gingerich, 1992) with the pos-
mations. It is possible that the reference to sibility that the lower part of the Qasr el Sag-
2002 GAFFNEY ET AL.: DACQUEMYS 5
TABLE 1 many of the specimens collected by the
Measurements of Dacquemys Skulls American Museum of Natural History, with
the help of Richard Markgraf, were obtained
SMNS DPC (Bown and Kraus, 1988). These sediments
12645 5986 represent the second of four faunal zones that
are recognized in the Jebel Qatrani Forma-
A. Midline length as preserved 73.28 79.48
tion (Rasmussen and Simons, 1991; Gagnon,
B. Maximum width 67.3 76.84
1997). Quarry B is thought to lie just below
C. Width between orbits 28.8 34.0 the EoceneOligocene boundary (Kappleman
D1. Width of left orbit 14.2 — et al., 1992; Rasmussen et al., 1992; Simons
and Chatrath, 1998), although the lack of
D2. Width of right orbit 14,2» 16.0
substantial faunal turnover across this bound-
E. Width of external nares 19.0 —
ary in the Fayum region led to some debate
F. Width of internal nares 13.7 — as to the exact placement of this boundary
G. Maximum height at quadrate 38.2 — (Gingerich, 1992; Van Couvering and Harris,
BOS):
H. Maximum width of skull 33.7 34.0»
taken at middle of orbits
DESCRIPTION
Length, anterior margin of prefrontals 98.8 100.1
—
to posterior margin of parietals
PREFRONTAL
Ji. Height of left orbit 13.5 —
Both prefrontals are preserved on both
J2. Height of right orbit 12.3 —
sides of SMNS 12645 and DPC 5986, al-
K. Skull height at occipital condyle 33.5 27.3 though its ventral process is complete only
L. Anterior width of triturating surface 15.2 — on the left side of SMNS 12645. The pre-
frontal of Dacquemys is similar to that in Po-
M. Posterior width of triturating surface 14.9 —
docnemis except for its much larger size, be-
N . Width of palate across 23.96 29.9
ing longer and wider. Erymnochelys and Pel-
foramina palatinum posterius
tocephalus have wider prefrontals than does
O. Length, front of skull to posterior 53.6 —
Podocnemis, but not as wide as in Dacque-
edge of condylus articularis
mys. The anterior projection of the prefrontal
aEstimated. extends to the anterior margin of the apertura
bDamaged. narium externa, not posterior to it as in Po-
docnemis.
ha along with the Birket Qarun Formation
FRONTAL
are close to the middle Eocenelate Eocene
(Bartonian-Priabonian) boundary (Holroyd et Both frontals are preserved in SMNS
al., 1996). Because the only other known 12645 and DPC 5986. Their ventral surface
specimen of Dacquemys was collected from is visible in DPC 5986. The frontal in Dac-
the lower sequence of the Jebel Qatrani For- quemys has the same contacts as in the living
mation, and it is difficult to know how much podocnemidids, but it differs in its greater
credence should be given to the reference to width. The orbits are visible in dorsal view
Diméh, the assignment of this specimen to in Podocnemis, Erymnochelys, and Peltoce-
one of these earlier formations must remain Phalus but not in Dacquemys. In ventral
tentative until further specimens are recov- view, Dacquemys has a much more extensive
ered. roof to the fossa orbitalis than in the living
The second specimen of Dacquemys (DPC genera. The sulcus olfactorius and fossa na-
5986) was collected by a Duke University salis are about the same size in the living
expedition from AMNH Quarry B (B-4). genera and Dacquemys, but the roof of the
Quarry B is located in the middle gravelly fossa orbitalis is more extensive in Dacque-
sandstone unit of the lower sequence of the mys, due mostly to the lateral extension of
Jebel Qatrani Formation (the lower fossil the frontal, although both the prefrontal and
wood zone of early authors) from which postorbital contribute to this.
6 AMERICAN MUSEUM NOVITATES NO. 3372
Fig. 2. Dacquemys paleomorpha, SMNS 12645, holotype, probably Jebel Qatrani Formation, Fa-
yum, Egypt. A, Dorsal; B, ventral; C, right lateral; D, anterior; E, left lateral; F, posterior. See figure 3
for key.
2002 GAFFNEY ET AL.: DACQUEMYS 7
Fig. 3. Dacquemys paleomorpha, SMNS 12645. Key to figure 2. Dotted lines indicate scale margins,
shaded areas are plaster, and hatched areas are broken edges.
PARIETAL contacts the frontal anteriorly, the postorbital
anterolaterally, and the quadratojugal later-
Most of the right parietal is preserved in
SMNS 12645, and all of the right and most ally. In Podocnemis there is a jugal-parietal
of the left are present in DPC 5986. As in contact that is absent in Peltocephalus and
the living genera, the parietal in Dacquemys Erymnochelys, as well as in Dacquemys. In
8 AMERICAN MUSEUM NOVITATES NOs3372
Fig. 4. Dacquemys paleomorpha, DPC 5986, Jebel Qatrani Formation, Fayum, Egypt. A, Dorsal;
B, ventral; C, right lateral. See figure 5 for key.
Dacquemys, however, there is a broad pari- Dhalus, which are more roofed than is Po-
etal-squamosal contact not seen in other po- docnemis. Dacquemys has a posterolaterally
docnemidids. The parietal extends posteri- expanded parietal which results in contact to
orly to a greater extent than in any other de- the squamosal.
scribed podocnemidid, completely covering The processus inferior parietalis is not well
the otic chamber. Posteromedially the parie- preserved in either Dacquemys specimen, but
tal contacts an expanded supraoccipital when it is best seen on the right side of DPC 5986.
compared with Erymnochelys and Peltoce- The processus contacts the supraoccipital pos-
2002 GAFFNEY ET AL.: DACQUEMYS 9
Ries, Dacquemys paleomorpha, DPC 5986. Key to figure 4. Dotted lines indicate scale margins,
hatched areas are broken edges.
teriorly and the prootic posteroventrally, and the jugal enters the orbit anteriorly, contacts
probably the pterygoid ventrally, all as in the the maxilla anteroventrally, the postorbital
recent podocnemidids. The more anterior con- anterodorsally, and the quadratojugal poste-
tacts and the formation of the foramen nervi riorly. Ventrally the jugal forms the anterior
trigemini are not preserved. part of the shallow cheek emargination. The
degree of cheek emargination in Dacquemys
JUGAL is far greater than in Erymnochelys and Pel-
The jugal is preserved in part in both tocephalus, but less than in Podocnemis and
skulls, but neither shows the internal rela- Hamadachelys. It is most comparable to
tions of the bone clearly. The lateral plate of Neochelys and Bauruemys.
10 AMERICAN MUSEUM NOVITATES NOs3372
The jugal in Dacquemys is small in com- tacts seen in most other podocnemidids, such
parison to the much larger jugal of Erym- as Neochelys. The postorbital enters the pos-
nochelys and Peltocephalus, in which the ju- terodorsal margin of the orbit as in the other
gal extends posteriorly to meet the quadrate, podocnemidids. The medial process of the
and the cheek emargination is quite reduced. postorbital is visible in DPC 5986 and con-
The medial process of the jugal is present in tacts the frontal dorsomedially, the jugal ven-
SMNS 12645, but its contacts are not clearly trolaterally, and the palatine ventromedially.
visible. As in the living podocnemidids, the
jugal does not appear to form any of the trit- PREMAXILLA
urating surfaces.
Both premaxillae are preserved in SMNS
12645, but neither is present in DPC 5986.
QUADRATOJUGAL
The premaxilla of Dacquemys contacts the
A nearly complete right quadratojugal is maxilla laterally and the other premaxilla
preserved in DPC 5986 and a partial one is medially. There is no vomer contact, as that
present on the right side of SMNS 12645. In bone is absent and the maxillae meet on the
midline behind the premaxillae as in Podoc-
Dacquemys, the quadratojugal contacts the
parietal medially, the squamosal posteriorly, nemis. Dacquemys is unique among Pelo-
the quadrate laterally, the postorbital antero- medusoides because the premaxillae are re-
dorsally, and the jugal anteroventrally. The cessed and not visible laterally. There is a
quadratojugal forms the dorsalmost part of shallow, anteroventral trough on the anterior
the margin of the cheek emargination. surface of each premaxilla, another feature
found only in Dacquemys. As far as can be
determined, the foramen praepalatinum is ab-
SQUAMOSAL
sent. The midline concavity on the triturating
The right squamosal is nearly complete in surface in Dacquemys is very deep, deeper
DPC 5986, and in SMNS 12645 the bone is than in Peltocephalus, and much deeper than
complete on the right side and partial on the in Podocnemis and Erymnochelys.
left. In Dacquemys the squamosal has a long
medial contact with the parietal that is absent MAXILLA
in all other described podocnemidids, and an
Both maxillae are preserved in SMNS
anterior contact with the quadratojugal that
12645, and both are absent in DPC 5986.
is comparable in size to the contact seen in
The vertical plate of the maxilla in Dac-
Peltocephalus and wider than in Podocnem-
quemys is shallower than in Podocnemis and
is. Medially the squamosal contacts the op-
Bauruemys and is comparable to Peltoce-
isthotic and anteromedially the quadrate, as
in other podocnemidids. The squamosal Phalus and Erymnochelys. The contacts are
forms part of the antrum postoticum (see as in the living podocnemidids. The horizon-
tal plate of the maxilla in Dacquemys has the
Quadrate). The posterior margin of the squa-
mosal in podocnemidids is a flange oriented same contacts as in Podocnemis expansa:
premaxilla anteromedially, other maxilla on
dorsolaterally to ventromedially and reaching
midline, palatine posteromedially, and jugal
the opisthotic. In most podocnemidids this
flange is a continuous sheet, but in SMNS posterolaterally. The midline maxilla contact
is more extensive than in Podocnemis expan-
12645 (it is absent in DPC 5986) the sheet,
as seen on the right side, curves anteriorly sa and Podocnemis unifilis, the only other
Pelomedusoides that have this character.
before reaching the opisthotic.
The triturating surface of Dacquemys is
characterized by two well-developed acces-
POSTORBITAL
sory ridges parallel to the lingual and labial
The postorbital is present but incomplete ridges. Similar accessory ridges occur in
on both sides of SMNS 12645, and is com- some species of Podocnemis (expansa, uni-
plete on the right side of DPC 5986. The filis, lewyana, vogli), but only in Dacquemys
postorbital of Dacquemys is not reduced as are they curved anteriorly to join each other
in Podocnemis and has the shape and con- close to the premaxilla-maxilla border.