Acleistochelys, a New Side-Necked Turtle (Pelomedusoides: Bothremydidae) from the Paleocene of Mali

2007·2.8 MB·English

by  Eugene S. Gaffney

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3549, 24 pp., 9 figures, 2 tables January 15, 2007
Acleistochelys, a New Side-Necked Turtle
(Pelomedusoides: Bothremydidae) from the Paleocene
of Mali
EUGENE S. GAFFNEY,1 ERIC ROBERTS,2 FAMORY SISSOKO,3
MOHAMED L. BOUARE´,4 LEIF TAPANILA,5 AND MAUREEN A. O’LEARY6
ABSTRACT
The Paleocene Teberemt Formation south of the Adrar des Iforas Mountains, between
Saguirilidad and In Fargas, Mali, yielded a nearly complete skull of a new genus and species of
side-necked turtle, Acleistochelys maliensis. Acleistochelys is a member of the family
Bothremydidae Baur, 1891, because: (1) the fossa precolumellaris is absent, (2) the foramen
stapedio-temporalefacesanteriorly,(3)theeustachiantubeisseparatedfromthestapesbybone,
and (4) an exoccipital-quadrate contact is present. Within the Bothremydidae, Acleistochelys
belongstothetribeTaphrosphyinibecause:(1)themaxilla-quadratojugalcontactisabsent,(2)the
palate is dorsally arched, (3) there is only a small contribution of the palatine to the triturating
surfaces, and (4) the septum orbitotemporale is at least partially open. Acleistochelys is most
closelyrelatedtoAzabbaremysbecausebothshareanarrowvomerlackingaposteriorattachment
tothe palatines.
The specimen was found in a marine limestone associated with crocodiles, echinoids, and
mollusks.
1DivisionofPaleontology,AmericanMuseumofNaturalHistory([email protected]).
2School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa
([email protected]).
3InstitutdesSciencesHumaines,Bamako,Mali.
4E´coleNationaledesInge´nieurs,Bamako,Mali.
5DepartmentofGeosciences,IdahoStateUniversity,Pocatello,ID83209-8072([email protected]).
6Department of Anatomical Sciences, Health Sciences Center T8 (040), Stony Brook University, Stony Brook, New
York,11794-8081,USA([email protected]).
CopyrightEAmericanMuseumofNaturalHistory2007 ISSN0003-0082
2 AMERICAN MUSEUMNOVITATES NO. 3549
INTRODUCTION po postorbital
pr prootic
The Bothremydidae is an extinct group of pt pterygoid
side-necked turtles recently reviewed and qj quadratojugal
expanded in content by Gaffney et al. (2006). qu quadrate
The purpose of the present paper is to name so supraoccipital
and describe a new bothremydid, based on sq squamosal
CNRST SUNY 199 from the Paleocene of vo vomer
Mali (Tapanila et al., 2004). The skull de-
scription follows the outline in Gaffney et al. GEOLOGY
(2006: appendix 1) for ease of comparison
with other bothremydids. Based on the phy- GEOLOGICAL SETTING
logenetic analysis of Gaffney et al. (2006),
During the latest Cretaceous (Campanian–
Acleistochelys maliensis is a member of the
Maastrichtian) through middle Eocene, the
tribe Taphrosphyini as characterized in
Trans-Saharan Seaway inundated portions of
Gaffney et al. (2006). Figures, descriptions,
central West Africa (Petters, 1979). In north-
and references to all of the bothremydid taxa
ern Mali, three transgressive–regressive cycles
referred to in this paper can be found in
are recorded by a relatively thin (,100 m)
Gaffney et al. (2006). The taxonomy also
sequence of sedimentary strata dominated by
follows that reference. The skull here named
sandstones, shales, limestones, and phos-
Acleistochelys maliensis isincluded inthedata
phates (e.g., Radier, 1959; Bellion et al.,
set of Gaffney et al. (2006: appendix 3) and is
1989; Moody and Sutcliffe, 1993; Tapanila et
shown in cladograms in figs. 288–314 as
al., 2004). These units were deposited in
CNRST SUNY 199. The reader should see
terrestrial, marginal marine, and open marine
this work for further discussion of this
settings within and along the margins of the
phylogenetic analysis.
Trans-Saharan Seaway, and they preserve
a rich vertebrate and invertebrate fossil re-
Institutional Abbreviations cord.
The Late Cretaceous–Paleogene Malian
AMNH American Museum of Natural
outcrops that are the focus of this study
History,New York
(fig. 1) are located in a narrow, half-graben
CNRST SUNY
Centre National de la Recherche structure, known as the Gao Trench or
ScientifiqueetTechnologique,Bama- ‘‘Detroit Soudanais.’’ Paleontologic investiga-
ko, Mali–Stony Brook University, tions of invertebrate faunas demonstrate that
New York theTrans-SaharanSeawaymayhaveprovided
FMNH Field Museum of Natural History, at times a dispersal route via the Gao Trench
Chicago for marine fauna between the Tethys Sea and
South Atlantic Ocean (Kogbe, 1981; Moody
Anatomical Abbreviations and Sutcliffe, 1993). Today this vast, desolate
region is characterized by expansive low-relief
bo basioccipital
plateausthatarecappedbyresistantlimestone
bs basisphenoid
beds. Small shifting dune fields and vast
ex exoccipital
stretches of desert pavement cover this region
fpcci foramen posterius canalis carotici
and obscure regional stratigraphic correla-
interni
fr frontal tions.
ju jugal
mx maxilla SEDIMENTOLOGYOF MALI 17
na nasal
op opisthotic Description
pa parietal
pal palatine The turtle specimen described herein was
pf prefrontal recoveredfromlocalityMali17,locatedsouth
pm premaxilla of the Adrar des Iforas Mountains, between
2007 GAFFNEY ETAL.: NEW SIDE-NECKED TURTLEFROM MALI 3
Fig. 1. Stratigraphic section of locality Mali 17, showing position of type specimen of Acleistochelys
maliensis n.gen., n.sp.
SaguirilidadandInFargas.Mali17issituated chalky, micritic limestone with thin shale
within a 6–10 m thick sequence of richly partings (unit 3) overlies this unit and
fossiliferous phosphatic sandstones, shales, preserves multiple articulated and associated
and limestones. The sedimentology at Mali turtle remains, including the specimen de-
17 is characterized by a basal 1 m thick white scribed in this report. Other well-preserved
to pale yellow phosphatic sandstone (unit 1) vertebrate and invertebrate fossils were also
with nodular chert concretions that grades recovered from this laterally extensive bed,
upward into a thin (0.5 m), dark gray sandy includingtheremainsofcrocodiles,encrusting
shale (unit 2) containing ray tooth plates and oysters (Ostrea multicostata), nautiloids
abundant bioturbation (fig. 1b). A 3 m thick (Deltoidonautilus sp.), gastropods (Gistortia
4 AMERICAN MUSEUMNOVITATES NO. 3549
sp.), and echinoids (e.g., Linthia sudanensis, TRIBETAPHROSPHYINIGAFFNEY,TONG,AND
Oriolampasmichelini).Theentiresuccessionis MEYLAN,2006
capped by a distinctive 2 m thick, cliff- SUBTRIBETAPHROSPHYINAGAFFNEY,TONG,
forming, blocky, recrystallized limestone bed ANDMEYLAN,2006
(unit 4). This unit preserves rare, moldic
Acleistochelys, new genus
nautiloids and abundant trace fossils.
TYPE SPECIES: Acleistochelys maliensis,
new species.
Interpretation
DISTRIBUTION: Paleocene of Mali.
Mali 17 represents an upward fining, retro- ETYMOLOGY: Aklystos, Greek for ‘‘shel-
gradationalmarinesequence.Increasingwater tered’’, or ‘‘hollowed’’, in allusion to the
depth is interpreted based on reduction of small, paired pits on the triturating surface;
siliciclastics and increasing purity of carbo- chelys, Greek for ‘‘turtle’’.
nates upward through the sequence. The DIAGNOSIS: A bothremydid pleurodire
fauna recovered from Mali 17 are consistent with these unique characters among the tribe
with relatively low-energy, normal marine Taphrosphyini: small pit formed by jugal,
conditions. maxilla, and palatine on triturating surface;
StrataofMali17likelybelongtothemiddle jugalexposedontrituratingsurface;accessory
to upper portion of the Teberemt Formation ridge present on anterior triturating surface;
of Moody and Sutcliffe (1991, 1993), which wide palatine-basisphenoid contact separating
they interpreted as Paleocene. Paleogene pterygoids on midline; supraoccipital-quad-
echinoderms, such as Oriolampas michelini rate contact present; basioccipital narrowly
and Linthia sudanensis, recovered from the enterscondylusoccipitalis;palatine-jugalcon-
turtle-bearingunit3precludeaCretaceousage tact in small septum orbitotemporale. Other
assignment, while putative Eocene (Ypresian) distinguishing characters are: skull relatively
vertebratesdocumentedfromstratigraphically longandnarrow;fossapterygoideusdeepand
higher phosphate conglomerates (fig. 1A; narrow as in Nigeremys but in contrast to
,68 m level) at nearby Tamaguilelt (Pascal Taphrosphys; foramen posterius canalis caro-
andTraore,1989;PattersonandLongbottom, ticiinterniformedbypterygoid,basisphenoid,
1989; Moody and Sutcliffe, 1993; O’Leary et and quadrate in contrast to Phosphatochelys;
al., 2006) provide an upper age limit. Moody small remnant of septum orbitotemporale
and Sutcliffe (1993) also correlated the present consisting of ventral parietal process
Teberemt Formation with a similar strati- as in Phosphatochelys but in contrast to
graphic sequence on the west side of the Taphrosphys.
Tilemsivalley,nearTichet,whichBellionetal. DISCUSSION: See table 1 for a comparison
(1989) dated as late Paleocene using benthic of genera in the tribe Taphrosphyini.
foraminifera and ostracodes. Based on faunal
analysis and detailed outcrop correlation with
strata exposed below and above Mali 17, we Acleistochelys maliensis, new species
tentatively agree with the Paleocene age
TYPE SPECIMEN: CNRST SUNY 199
assignment of Moody and Sutcliffe (1991,
(figs. 2–5), partial skull including fragments
1993) for these deposits, although an early
of the lower jaw, lacking some of the left
Eocene age cannot necessarily be precluded.
temporal region, and both posterior parts of
the skull roof. Skull measurements are in
table 2.Associatedshellfragmentsincludethe
SYSTEMATICS
anterior margin of the nuchal (fig. 6), neurals
one and four (fig. 7), and peripheral two
(fig. 7). A partial cervical vertebra (figs. 8, 9)
ORDERTESTUDINESLINNEAUS1758OR
BATSCH1788 and some pelvic fragments are present.
TYPE LOCALITY: Mali 17, located south of
INFRAORDERPLEURODIRACOPE,1864
the Adrar des Iforas Mountains, between
FAMILYBOTHREMYDIDAEBAUR,1891 Saguirilidad and In Fargas, Mali.
2007 GAFFNEY ETAL.: NEW SIDE-NECKED TURTLEFROM MALI 5
HORIZON: Middle to upper portion of the Structures: The frontal in Acleistochelys
Teberemt Formation of Moody and Sutcliffe enters the orbital margin, similar to that seen
(1991, 1993). in Azabbaremys and Nigeremys.
DEPOSITIONAL ENVIRONMENT: Near shore
marine. PARIETAL
DIAGNOSIS: As for genus.
ETYMOLOGY: Named for the country of Preservation: Both parietals are present
discovery. butdamaged. Thedorsalplate ontheleftside
REFERRED MATERIAL: None. retains only its anteromedial portion. The
PREVIOUS WORK: CNRST SUNY 199 is right dorsal plate is more complete laterally,
included in the phylogenetic analysis of but it also lacks all of the temporal margin.
Gaffney et al. (2006). The processus inferior parietalis, however, is
nearly complete on both sides, the left one
having some breakage ventrally.
DESCRIPTION Contacts of dorsal plate: The dorsal plate
PREFRONTAL in CNRST SUNY 199 preserves the midline
parietal contact and the medial part of the
Preservation: Both prefrontals are present: frontal contact anteriorly. The right parietal
the right one is nearly complete, the left is has the anterolateral contact with the post-
missing some of its lateral edge. orbital preserved.
Contacts: The prefrontal in Acleistochelys Structures of dorsal plate: The degree of
has the same contacts as in Azabbaremys, temporal emargination in Acleistochelys, al-
Nigeremys,andArenila:prefrontalonmidline, though not determinable exactly, was proba-
maxilla anteroventrally, and frontal poste- bly not as extensive as in Nigeremys, because
riorly.Thereisnopalatineorparietalcontact. the remaining broken margin is relatively
Structures: The dorsal plate of the pre- thick and extends about as far as the natural
frontal in Acleistochelys is similar to that in margin in Nigeremys (and probably Arenila,
Azabbaremys, but not strongly convex dorsal- although that skull also lacks most of the
ly as in Azabbaremys. The dorsal margin of parietal dorsal plate).
the apertura narium externa in Acleistochelys Theseptumorbitotemporale(seeGaffneyet
is well posterior to the ventral margin in al., 2006: fig. 78) in the tribe Taphrosphyini,
contrast to Azabbaremys in which the dorsal may be reduced or absent (Gaffney et al.,
margin is almost directly above the ventral 2006: character 28). This is best seen in
margin. Phosphatochelys (Gaffney et al., 2006: fig.
The size of the fossa nasalis and sulcus 202). However, the group that lacks the
olfactorius are similar in both Acleistochelys septum (that is, Taphrosphys, Labrostochelys,
and Azabbaremys. The ventral process of the Rhothonemys, Ummulisani) also lacks the
prefrontal is narrow in Acleistochelys. ventral parietal process seen in Phospha-
tochelys (Gaffney et al., 2006: fig. 202). This
FRONTAL process is a remnant of the lateral wall of the
septum orbitotemporale and reaches the pal-
Preservation: The right frontal in CNRST atine above the base of the processus tro-
SUNY 199 is nearly complete; it is missing chlearis pterygoidei lateral to the sulcus
only its posterolateral corner. The left one is palatinopterygoideus.Thisprocessalsooccurs
missing most of its lateral half. in Acleistochelys, although there are differ-
Contacts: The frontal in Acleistochelys ences from Phosphatochelys: In Acleistochelys
contacts the prefrontal anteriorly, the other it is thinner and longer, and contacts the
frontal medially, the postorbital posterolater- palatine only, whereasinPhosphatochelys itis
ally, and the parietal posteriorly, all as in wider and shorter and contacts the palatine
Azabbaremys, Nigeremys, and Arenila, and in anteriorly and the pterygoid posteriorly. The
contrasttoPhosphatochelysandRhothonemys, entire ventral portion of the septum orbito-
which lack a postorbital contact. temporale remnant differs in Acleistochelys
6 AMERICAN MUSEUMNOVITATES NO. 3549
s
y
el
h
c
o
Acleist nono yesbroadnoyes?yesnonoyes smallnonoyesyes yes yesyes yesyesno nonono noabsentnowide
ni
a
s
Ummuli noyes no?yesnoabsentnoyesyesno largeyesyesno? ? nono nonono nonoyes yesabsentnowide
s
y
m
w
othone noyes yesbroadyes??nonoyes? largenono?? no no? ?nono ?no? ?smallnonarro
h
R
a
nil
Are nono yes????nono?no ?nononono no nono no?? nono? no??wide
mys no
yini Nigere nono yes??no?nonoyes? smallnonono? ? nono probably?no nono? ?absentnowide
h s
p y
hros ochel
BLE1ribeTap Phosphat nono nobroadyesnoabsentnoyesnono largenoyesnono yes nono nonono yesyesyes yessmallnowide
AT
The mys
t e
neraof Azabbar nono yesbroadnonopresentnoyesyesno smallnononono no nono nonoyes nonono noabsentnowide
e
G s
Labrostochely yesyes yesnarrowyesyespresentyesnoyesno smallnonono? ? nono nonono nonono nosmallnoverynarrow
s
y
Taphrosph nono yesnarrowyesnopresentnononono smallnononono no ?no nonono yes&nonono nosmallyesnarrow
PrefrontalextremelylongandnarrowAperturanariumexternaatleastpartiallydividedFrontalinorbitalmarginJugalSquamosalwithverticalflangeSquamosalelongatedposteriorlyQuadratojugal-jugalcontactSkulllongandnarrowSkullshortPremaxillaprojectspastlabialridgeBasioccipitalenterscondylusoccipitalisAperturanariumexternaPrefrontalhornPF-PARcontactJugalexposedontrituratingsurfacePalatine-jugalcontactinseptumorbitotemporaleParietalformingatleastpartofseptumorbitotemporalePitontrituratingsurfaceAccessoryridgeonanteriorpartoftrituratingsurfaceWidepalatine-basisphenoidcontactSQ-QUcontactPrefrontalextendstoanterioredgeofpremaxillaCheekemarginationPreorbitalregionveryshortVerylargequadratecoveringhalfofcheekForamennervitrigeminitroughAntrumpostoticumSulcuseustachiiopenmoreventrallyInterorbitalwidth
2007 GAFFNEY ETAL.: NEW SIDE-NECKED TURTLEFROM MALI 7
ys U al
Acleistochel no largeyeswideno nonoyesnoanterior present open no no ThicknoyesnarrowernonoPT,BS,Q morevertic no no yes
Ummulisani yesyes smallyesnarrowno noyesno?anterior absent open no no thin?nonarrowernoyesQU&QUPT+morehorizontalno no yes
s
y
m
e
hothon yesyes smallyes?? ????? ? open no no thick???yesno? ? ? ? yes
R
Arenila no? ?nonarrow? yesnonoyesposterior deep&narrowclosed no no verythickyesyes???BS,PT ? ? no no
w
Nigeremys no? ?nonarrowno yesnonoyesposterior deep&narro closed no no verythickyesyesnarrower??? morevertical no no no
s
TABLE1(Continued) AzabbaremysPhosphatochely noyesnoyes smallsmallyesyeswidewidenono nonononononono?anteriorposterior absentabsent openopen yesno nono thickthicknoIndetyesyesnarrowernarrowernoyesnonoPT,QUPT,QU moreverticalmorevertical nono nono yesyes
s
y
hel al
Labrostoc no? ?nowideyes nonoyesnoanterior absent ? no yes thinyesnowideryesnoPT,QU morehorizontyes yes no
Taphrosphys noyes ?no?yes noyesno?anterior absent open no yes thin?nowideryesyesPT,BS,QU morevertical yes ? ?
ParietalentersorbitalmarginParietalformspostorbitalwallandpocketMedialprocessofjugalMaxilladeepSulcuspalatinopterygoideusVentrallyopeningchannelatbackofskullBasisphenoidV-shapedBasisphenoidpentagonalBasisphenoidtriangularandelongateVomerrobustCondylusmandibularispositioninrelationtocondylusoccipitalisFossapterygoidei SeptumorbitotemporaleatleastpartiallyopenProminentcrenellationsontrituratingsurfaceTrituratingsurfaceonmaxillathincurvedtroughLabialridgeonmaxillaMaxilla-vomercontactDorsallyarchedpalateCavumtympaniSulcuseustachiiwithdorsalprocessSulcuseustachiiwithventralprocessForamenposteriuscanaliscaroticiinterniformedbyFenestrapostotica PosteroventrallyopeningconcavityonquadrateProcessustrochlearispterygoideiverysmallPostorbitallackingmedialprocess
8 AMERICAN MUSEUMNOVITATES NO. 3549
Fig. 2. Acleistochelys maliensis n.gen., n.sp. Partially restored skull based on CNRST SUNY 199. A,
dorsal; B, ventral;C, rightlateral.
and Phosphatochelys in the position of the damaged, the processus inferior parietalis in
jugal and palatine (see Jugal, Palatine). Acleistochelysseemstoberelativelythin,asin
Whether this structure should be considered Azabbaremys, but still seems to contact the
homologous in Acleistochelys and Phospha- palatine, a condition that is unclear in
tochelys is a fascinating question. Azabbaremys.
Contacts of processus inferior parietalis: Structures of processus inferior parieta-
In Acleistochelys the vertical wall of the lis: The foramen interorbitale is relatively
parietal contacts the pterygoid ventrally, large in Acleistochelys, as in Azabbaremys
the prootic posteroventrally, and the sup- and Phosphatochelys, and the processus in-
raoccipital posteriorly. Although somewhat ferior parietalis is narrow, also as in
2007 GAFFNEY ETAL.: NEW SIDE-NECKED TURTLEFROM MALI 9
Fig. 3. Acleistochelys maliensis n.gen., n.sp. Partially restoredventral viewof CNRST SUNY 199.
Azabbaremys. The foramen nervi trigemini, and the right preserves the anterodorsal
preservedonbothsides,isformedbytheusual margin. The medial process on both sides is
bones: parietal anterodorsally, prootic pos- present.
terodorsally, and pterygoid ventrally. Contacts of lateral plate: The jugal in
Acleistochelyshasalonganteroventralcontact
JUGAL with the maxilla as in Azabbaremys and at
least an anterodorsal contact with the post-
Preservation: Neither jugal is complete, orbital, but the length of the bone is in-
both are missing their posterodorsal margins. determinate. The jugal contacts the quadrate
The left jugal preserves the ventral margin, posteroventrally in a suture that is more
10 AMERICAN MUSEUMNOVITATES NO. 3549
Fig.4. Acleistochelysmaliensisn.gen.,n.sp.PhotographsofCNRSTSUNY199.A.dorsal;B,ventral;
C,anterior; D, rightlateral; E, posterior; F, leftlateral.