Sankuchemys

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    Copyright American Museum of Natural History 2003 ISSN 0003-0082

    P U B L I S H E D B Y T H E A M E R I C A N M U S E U M O F N A T U R A L H I S T O R Y

    CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024Number 3405, 10 pp., 3 figures, 1 table May 22, 2003

    Sankuchemys, a New Side-Necked Turtle

    (Pelomedusoides: Bothremydidae) from theLate Cretaceous of India

    EUGENE S. GAFFNEY,1 ASHOK SAHNI,2 HERMAN SCHLEICH,3

    SWARN DEEP SINGH,4 AND RAHUL SRIVASTAVA5

    ABSTRACT

    The Maastrichtian Deccan Intertrappean beds of Amboli Quarry, Bombay, yielded the skullof a new genus of side-necked turtle. Sankuchemys sethnai, new genus and species, is apelomedusoid pleurodire belonging to the family Bothremydidae Baur, 1891, based on thesecharacters: (1) exoccipital-quadrate contact, and (2) foramen stapedio-temporale not visible indorsal view. Sankuchemys is most closely related to Kurmademys from the Maastrichtian ofTamil Nadu, because among bothremydids they uniquely share a highly emarginated temporalroof and a small postorbital. Sankuchemys is unique among bothremydids in having an ac-cessory ridge on the triturating surface.

    INTRODUCTION

    Singh et al. (1998) announced the discov-ery of a bothremydid skull in a fauna dated

    1 Curator, Division of Paleontology, American Museum of Natural History. e-mail: [email protected] Centre of Advanced Studies in Geology, Panjab University, Chandigarh, India. e-mail: [email protected] Director, Fuhlrott-Museum and Forschungsinstitut, Auer Schulstrasse 20, D-42103 Wuppertal, Germany. e-mail:

    [email protected] Institute of Petroleum Exploration, Oil and Natural Gas Corporation, 9, Kaulagarh Road, Dehra Dun 248001,

    India. e-mail: [email protected] Department of Geology, Lucknow University, Lucknow-226007, India. e-mail: [email protected]

    as Maastrichtian from the fossiliferous in-tertrappean tuff of the Bombay region. Thepurpose of this paper is to name and de-scribe this specimen. Although the skull is

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    crushed nearly flat, it does retain enoughmorphology to diagnose it as a new taxon,and to make useful comparisons with relatedtaxa.

    Pleurodires are absent in the recent faunaof India, but they are known as fossils fromthe Late Cretaceous into the Neogene(Wood, 1970; Broin, 1987b, 1988; Jain,1986). Nonetheless, fossil pleurodires in In-dia are rare, and only two other Indian pleu-rodire taxa are known from skulls: a podoc-nemidid, Shweboemys pisdurensis (Jain,1977, 1986), and a bothremydid, Kurmade-mys kallamedensis (Gaffney et al., 2001b).

    The cranial morphology terms used hereare described in Gaffney (1979), which alsocontains a literature review to that date. Ref-erences to the higher categories used hereare in Gaffney et al. (2001a, 2001b). Otherrecent papers on bothremydids are Lappar-ent de Broin and Werner (1998), Gaffney etal. (2001c), and Tong and Gaffney (2000).

    INSTITUTIONAL ABBREVIATIONS

    SDS/VPL Vertebrate Paleontology Laboratory,Centre of Advanced Studies in Ge-

    ology, Panjab University, Chandi-garh, India

    ANATOMICAL ABBREVIATIONS

    bo basioccipitalbs basisphenoidex exoccipitalfnt foramen nervi trigeminifpcci foramen posterius canalis carotici inter-

    nifr frontal

    fst foramen stapedio-temporale ju jugal

    mx maxillaop opisthoticpa parietalpal palatinepf prefrontalpm premaxillapo postorbital

    pr prooticpt pterygoidqj quadratojugal

    qu quadrateso supraoccipitalsq squamosal

    SYSTEMATICS

    ORDER TESTUDINES LINNAEUS, 1758

    MEGAORDER PLEURODIRA COPE, 1864

    (FIDE GAFFNEY AND MEYLAN, 1988)

    HYPERFAMILY PELOMEDUSOIDES COPE, 1868

    FAMILY BOTHREMYDIDAE BAUR, 1891

    Sankuchemys, new genus

    TYPE SPECIES: Sankuchemys sethnai, newgenus and species.

    DISTRIBUTION: Maastrichtian of Bombay,India.

    ETYMOLOGY: Sankuch, compressed inSanskrit, in allusion to the remarkablycrushed type specimen.

    DIAGNOSIS: A genus of bothremydid pleu-rodire with triangular skull, orbits dorsolat-erally placed; extensive temporal emargina-tion and small postorbital as in Kurmademys(Gaffney et al., 2001b) and in contrast to allother bothremydids; triturating surfacesroughly parallel and without pits, but withaccessory ridge parallel to labial ridge uniqueamong bothremydids; foramen posterius ca-nalis carotici interni formed by pterygoid and

    basisphenoid in contrast to basisphenoid onlyin Kurmademys; foramen stapedio-temporalenot visible in dorsal view as in other both-remydids, but in contrast to Kurmademys;prootic and foramen nervi facialis exposed inventral view as in Kurmademys.

    DISCUSSION: Although many characters arevisible in the type skull of Sankuchemys, oneimportant area completely wrecked in SDS/VPL 1125 is the cavum tympani. This regionhas many characters important in bothremy-did systematics (Gaffney et al., 2001a,2001b) that are not determinable for this tax-on. The occiput is also reduced to two di-mensions completely obscuring foramina andfeatures in that area. Nonetheless, SDS/VPL1125 does preserve enough characters toshow its distinctness from all other taxa andto test its relationships using currently avail-able hypotheses.

    Sankuchemys sethnai, new species

    TYPE SPECIMEN: SDS/VPL 1125, a com-plete skull completely smashed flat.TYPE LOCALITY: Amboli Quarry, Jogesh-

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    Fig. 1. Sankuchemys sethnai, n. gen. and sp. SDS/VPL 1125. Maastrichtian green tuff of AmboliQuarry, Bombay. Partially restored views. A, Dorsal; B, ventral.

    wari, Bombay, India (map and faunal discus-sion in Singh et al., 1998).

    HORIZON: Green tuff bed of Amboli, Inter-trappean beds, late Maastrichtian (discussionin Singh et al., 1998).

    DIAGNOSIS: As for genus.ETYMOLOGY: In honor of the discoverer of

    the holotype skull, Prof. S.F. Sethna, knownfor his pioneering work on the geology ofthe Mumbai region.

    DESCRIPTION

    PREFRONTAL

    Both prefrontals are present but crushedventrally, disarticulated and overlain by thedorsal processes of the maxillae. There is noanterior projection as preserved.

    FRONTAL

    Both frontals are present, slightly fracturedbut complete. The frontal in Sankuchemys

    has the usual bothremydid contacts seen inKurmademys (Gaffney et al., 2001b) andCearachelys (Gaffney et al., 2001a).

    PARIETAL

    Both parietals are present, but they arecracked and crushed ventrally. Only the dor-sal surface is visible. There is an anteriorcontact with the frontal and anterolateralcontact with the postorbital as in Kurmade-mys and Galianemys (Gaffney et al., 2002b).In contrast to all other Bothremydidae exceptKurmademys, the parietal of Sankuchemysshows an extreme condition of the temporalemargination. The parietal in these two taxahas very little overhang onto the fossa tem-poralis, and its posterolateral portion is large-ly missing in comparison to other Bothre-mydidae.

    JUGAL

    Both jugals are present in Sankuchemys,but they are cracked and displaced from theiroriginal articulations so that the relations ofthe medial process are ambiguous. The jugalin Sankuchemys contacts the maxilla anteri-orly, the postorbital dorsomedially, and the

    quadratojugal posteriorly. It enters the pos-teroventral edge of the orbital margin. Aspreserved, it is very similar to the jugal in

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    Kurmademys, and differs from Cearachelysin its orbital exposure.

    The triturating surfaces and palate are wellenough preserved to show that the jugal doesnot form a significant part of the palate as inbothremydids like Bothremys (Gaffney andZangerl, 1968).

    QUADRATOJUGAL

    At least portions of both quadratojugalsare present in Sankuchemys, although theyare badly broken due to crushing and theirrelations are unclear in some areas. Thequadratojugal contacts the jugal anteriorlyand the postorbital anteromedially. As pre-

    served, the jugal, on both sides, completelyprevents a maxilla-quadratojugal or maxilla-quadrate contact. The absence of a goodquadratojugal (and good quadrate as well)makes it difficult to be sure that this was thecase originally. Quadrate and squamosal con-tacts with the quadratojugal are obscured bypreservational breakage. The formation of atleast part of the lateral margin of the fossatemporalis by the quadratojugal is clear andappears to be similar to the condition in Kur-mademys and Cearachelys.

    SQUAMOSAL

    At least part of both squamosals are pre-sent, but the bones are poorly preserved. Aspreserved, the squamosal in Sankuchemysshows the anteromedial quadrate contact onthe ventral surface, and the medial opisthoticcontact, both found in all other pelomedu-soides. The complete obliteration of the ca-vum tympani prevents any information beingavailable about the antrum postoticum and itsformation by the squamosal.

    POSTORBITAL

    The postorbital is preserved on both sidesof Sankuchemys; both are badly fractured,but the relations and contacts on its externalsurface can be determined. The postorbital inSankuchemys contacts the frontal anterome-dially, the parietal posteromedially, the jugalanterolaterally, and the quadratojugal pos-

    terolaterally. The postorbital widely entersthe orbit on its posterior margin, and it entersthe margin of the temporal emargination pos-

    teriorly. The size and relations of the post-orbital in Sankuchemys are very similar tothe postorbital in Kurmademys. AmongBothremydidae, the postorbital in Sankuche-mys and Kurmademys is shortest, being closeto the small size in Pelomedusidae. This isrelated to the extent of temporal emargina-tion.

    The presence of a medial postorbital pro-cess is not determinable in Sankuchemys dueto crushing; however, the skull is thicker inthis area and there are bone fragments in thecorrect place.

    PREMAXILLA

    Both premaxillae are present and relativelywell preserved. The contacts of the premax-illa in Sankuchemys in ventral view are withthe maxilla laterally, the other premaxillamedially, and the vomer posteromedially.Contacts on the dorsal surface are not visible.The labial ridge is acute with a sharp ridgeas in Kurmademys, but it is thicker dorsally.The size of the premaxillary posterior shelfbearing the triturating surface is nearly thesame in both genera, but Kurmademys has adeep median concavity that is absent in Sank-

    uchemys.

    MAXILLA

    Most of both maxillae are preserved inSankuchemys, but there is considerable dam-age due to crushing. The dorsal surface con-tacts are the premaxilla anteriorly, the pre-frontal anterodorsally, and the jugal posteri-orly. The posterior limits of the maxilla aredamaged, and it is possible that a quadrato- jugal contact was present beneath the jugal.

    The ventral contacts are the premaxilla an-teromedially, the palatine posteromedially,and the jugal posteriorly. As preserved, themaxilla does not contact the vomer and thisseems to be original. The region of the pal-atine-pterygoid-jugal contact is a mush onboth sides, so these relations are unclear.

    The maxilla of Sankuchemys differs fromKurmademys, Cearachelys, and Bothremysin having a more parallel-sided trituratingsurface rather than a triangular one, expand-

    ed posteriorly. The labial ridge is acute andsharp as in Kurmademys and Cearachelys,but may be thicker dorsally, although this

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    may have been caused by crushing. The me-dial edge of the triturating surface is not par-ticularly well preserved, but the posterior ex-pansion seen in Kurmademys and Cearach-elys seems to be absent. It is possible thatthis is a consequence of the poor preserva-tion, as the lingual ridge marking the tritu-rating surface edge is very low. However,Sankuchemys does have a more expanded an-terior part of the triturating surface than doother bothremydids, and this is not preser-vational. The triturating surface of Sankuche-mys is unique among bothremydids in havingan accessory ridge parallel to the labial ridgeand extending the complete length of themaxilla. This ridge is much lower than the

    labial ridge, and its height is constant alongits length. It seems to begin on the premaxillain a rugose area, and runs to the maxilla- jugal suture. No other bothremydid has anaccessory ridge on the triturating surface, al-though such ridges do occur in podocnemi-dids (Dacquemys, Gaffney et al., 2002a).

    VOMER

    Sankuchemys has a well-preserved, al-though fractured, vomer. It contacts the pre-

    maxillae anteriorly and the palatines poste-riorly. In available Kurmademys specimensthe vomer is not preserved. In Cearachelysit has the same contacts and is similar to thevomer in Sankuchemys. The vomer separatesthe paired apertura narium interna, which, inSankuchemys is oval and about the same sizeas in Kurmademys and Cearachelys.

    PALATINE

    At least some of both palatines are pre-

    served in Sankuchemys, but these thin bonesare badly fractured due to crushing. The pal-atine in Sankuchemys has the usual bothre-mydid contacts: vomer anteromedially, pal-atine medially, pterygoid posteriorly, andmaxilla anterolaterally.

    As preserved, the palatine in Sankuchemysagrees with that bone in Kurmademys exceptfor one feature. The palatine in Sankuchemysdoes not extend anterolaterally to form partof the triturating surface as in Kurmademys

    and Cearachelys.Only a small part of the dorsal surface ofthe palatine is visible in the orbital opening

    in Sankuchemys. The complete crushing ofthe skull precludes information on the sulcuspalatinopterygoideus and foramen orbito-na-sale.

    A small part of the foramen palatinumposterius is present on the left palatine. It isconsistent in size and position with that inKurmademys.

    QUADRATE

    Both quadrates are present, but they are socrushed dorsoventrally that the presence of acavum tympani can only be inferred, not ob-served. The ventral surface of the quadrateis better preserved than the dorsal surface,

    which is badly fractured.In dorsal view the quadrate of Sankuche-

    mys contacts the prootic anteromedially andthe opisthotic posteromedially. Many of thesutures in this area are obscured by breakage,but it seems that there is no quadrate-supra-occipital contact as in Kurmademys andCearachelys; however, one could be present(see Supraoccipital). As preserved, the quad-rate lacks an anterior process contacting themaxilla, and the size of the jugal suggests

    that this was the case originally.In ventral view, the quadrate contacts thepterygoid anteromedially, the basisphenoidand prootic medially, and the basioccipitalposteromedially, with all contacts beingfound in Kurmademys and Galianemys em-ringeri as well. The quadrate also contactsthe exoccipital as in all other bothremydids.The opisthotic contact is visible but is badlyobscured by crushing. Posterolaterally thesquamosal contact is also visible but badlydamaged.

    On the left side in lateral view there is athin layer of matrix representing the crushedcavum tympani. All its associated featuresincisura columellae auris, antrum postoticumand suchare not determinable. On the dor-sal surface, the position of the foramen sta-pedio-temporale in the prootic suture is alsonot determinable. Some of the quadrate-pro-otic suture is visible, enough to determinethat the foramen stapedio-temporale is notpresent dorsally. The condylus mandibularis

    has been crushed, but it does not seem tohave been moved significantly from its orig-inal position. The condylus mandibularis is

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    Fig. 2. Sankuchemys sethnai, n. gen. and sp. SDS/VPL 1125. Maastrichtian green tuff of AmboliQuarry, Bombay. A, Ventral; B, dorsal; C, right lateral; D, anterior; E, left lateral; F, posterior.

    well anterior to the condylus occipitalis as inKurmademys, and it is not as far posterior asin Cearachelys.

    PTERYGOID

    Both pterygoids are present but badly frac-tured. Only the ventral surface is visible. Thepterygoid in Sankuchemys contacts the pal-atine anteriorly, the quadrate posterolaterally,the other pterygoid medially, and the basi-sphenoid posteromedially, as in both Kur-mademys and Cearachelys. There is alsocontact with the prootic posteriorly betweenthe quadrate and basisphenoid (see Prootic)

    as in Kurmademys.The processus trochlearis pterygoidei ispartially preserved on both sides and appears

    to be directed laterally at nearly right anglesto the midline, much as in Kurmademys andCearachelys. The quadrate ramus is defined

    by sutures on both pterygoids but is badlyfractured. The question of a deep M. ptery-goideus attachment concavity as found inKurmademys cannot be answered definitelyfor Sankuchemys due to poor preservation;however, there is some evidence that one waspresent. The prootic surface on the right side(see Prootic) is crushed, and the quadrate ra-mus of the pterygoid that is continuous withthe prootic here forms a curved surface that,if restored, seems to be the lateral wall of a

    depression similar in depth to that in Kur-mademys. Even though in its present condi-tion, there is no M. pterygoideus concavity

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    Fig. 3. Key to figure 2.

    in Sankuchemys, it is likely that one was pre-sent.

    The position of the foramen posterius ca-nalis carotici interni is also not definite inSankuchemys, although the damaged rem-nants of both can be seen. The foramen ap-pears to be formed by pterygoid anteriorlyand basisphenoid posteriorly. On the betterpreserved right side, the foramen posteriuscanalis carotici interni lies at the edge of adistinct dorsally curved surface of the pter-ygoid, further evidence of an M. pterygoi-deus depression with the foramen in its an-

    terior wall. On the right side the posterior ordorsal margin of the foramen seems to beformed by the basisphenoid, but the area is

    badly fractured and it could be prootic. How-ever, on the left side, there seems to be a

    posterodorsal margin for the foramen that isbasisphenoid. The pterygoid portion of theforamen posterius canalis carotici interni ismore damaged here, unfortunately. Due tocrushing, the left pterygoid has little evi-dence of a depression, and the pterygoidmargin of the foramen posterius canalis car-otici interni is damaged.

    The area where the foramen palatinumposterius would be expected is badly brokenon both sides; however, a margin of the fo-

    ramen is present on the right palatine, andthe pterygoid margin as preserved is consis-tent with this.

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    SUPRAOCCIPITAL

    The supraoccipital is present in Sankuche-mys and relatively well preserved comparedwith the rest of the awful mess. The crista

    supraoccipitalis is partially preserved with itsmain surface still vertical. Its dorsal and pos-terior edges are broken. The laterally ex-panded base of the supraoccipital shows aclear anterior suture with the parietal on bothsides. Posterolaterally the exoccipital sutureis present on the left side. Laterally on bothsides the more anterior prootic and more pos-terior opisthotic sutures are discernable butnot definitive. There are a number of brokenareas that could represent these sutures. The

    systematically important lateral lappet of thesupraoccipital that contacts the quadrate isquestionable. Given the state of preservationit could be present or absent. There areenough cracks that could be sutures to sup-port either interpretation.

    EXOCCIPITAL

    Both exoccipitals are present but crushed,although they retain enough three-dimen-sionality to allow some definition of the fo-

    ramen magnum. On the dorsal surface theexoccipital has the usual contacts: supraoc-cipital dorsally, opisthotic laterally, quadrateventrolaterally, and basioccipital ventrome-dially.

    The foramen magnum margins are visibleand, although broken, the base of the con-dylus occipitalis is present on both sides. Thecondylus occipitalis is formed only by theexoccipitals. Parts of the medial margins ofthe foramen jugulare posterius are identifi-able, but whether it was closed is not deter-minable. No foramen nervi hypoglossi is vis-ible.

    BASIOCCIPITAL

    The basioccipital in Sankuchemys contactsthe basisphenoid anteriorly, the quadrate lat-erally, and the exoccipitals posterolaterally,all as in Kurmademys and other bothremy-dids. The condylus occipitalis is not well pre-served, but the posterior end of the basioc-

    cipital pinches out before entering whatseems to be the articular surface of the con-dylus occipitalis. There is evidence of a low

    tuberculum basioccipitale, possibly devel-oped to the extent seen in Kurmademys.There is no evidence of a median concavity,but one could have been present. As pre-served, the basioccipital in Sankuchemys isslightly longer relative to its width than inKurmademys.

    PROOTIC

    The exposure of the prootic in Sankuche-mys is in an area of broken bone, but suturesand sutural surfaces are visible on both sides.As exposed in ventral view the prootic inSankuchemys is a narrow, oval bone con-tacting the pterygoid anterolaterally, the ba-

    sisphenoid medially, and the quadrate pos-terolaterally. The prootic exposure in Sank-uchemys is similar to that in Kurmademys inits position, shape, and amount of exposure.In Kurmademys this exposure seems to berelated to the development of a deep fossapterygoideus, but there is no evidence of afossa in Sankuchemys. The extensive crush-ing has probably obscured this depression.

    In the center of the prootic in Sankuche-mys is a foramen, the foramen nervi facialis,for the facial nerve (VII). This foramen is

    also exposed in the center of the prootic inKurmademys and Galianemys emringeri.

    On the dorsal surface both prootics arepoorly preserved, but they are well enoughpreserved to show that a foramen stapedio-temporale is not visible. The anterior surfaceof the prootic where this foramen and theforamen nervi trigemini would be expectedis not preserved. On the dorsal surface theprootic contacts the supraoccipital postero-medially and the quadrate laterally. The

    question of a prootic-opisthotic contact can-not be determined confidently, but it is likelythat one was present.

    OPISTHOTIC

    Although both opisthotics are present inSankuchemys, transforming a complex three-dimensional element into two dimensionswas not very kind to its morphology. On theventral surface of both sides these contactsare visible: quadrate anterolaterally, squa-

    mosal posterolaterally, and exoccipital pos-teromedially. The opisthotic contacts the su-praoccipital anteriorly and the quadrate lat-

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    TABLE 1

    Measurements of Sankuchemys sethnai SDS/VPL 1125 (in millimeters)

    A. Midline length as preserved

    B. Maximum width

    C. Width between orbitsD1. Width of left orbit

    D2. Width of right orbit

    48.8

    49.3

    9.013.1

    11.5

    E. Width of external nares

    F. Width of internal nares

    G. Maximum height at quadrate

    H. Width of skull at middle of orbits

    I. Length from anterior margin of prefrontals to posterior margin of supraoccipital

    11.2

    11.9a

    9.7a

    30.3a

    44.5a

    J1. Height of left orbit

    J2. Height of right orbit

    K. Skull height at occipital condyle

    L. Anterior width of triturating surface

    M. Posterior width of triturating surface

    N. Width of palate across foramina palatinum posterius

    O. Length from front of skull to posterior edge of condylus articularis

    5.5a

    6.7a

    9.4a

    5.5

    7.0

    14.1a

    33.2a

    a Damaged.

    erally in dorsal view. The probable prooticcontact is discussed under Prootic and Su-praoccipital.

    Few of the occipital structures and foram-ina can be made out in Sankuchemys. On the

    left side there is an opening that could beinterpreted as what is left of the fenestrapostotica.

    BASISPHENOID

    The basisphenoid is present in Sankuche-mys but it is fractured. It has the usual both-remydid contacts: pterygoid anterolaterally,quadrate posterolaterally, and basioccipitalposteriorly. In addition there is the short, lat-eral contact with the prootic, also found in

    Kurmademys and Galianemys emringeri. Thepterygoid contact includes a short anterolat-eral projection, presumed to be basioccipital,forming the posterior margin of the foramenposterius canalis carotici interni (see Ptery-goid).

    RELATIONSHIPS

    Sankuchemys is missing some importantmorphologic areas, particularly the cavumtympani, that would help test its relation-

    ships. However, enough characters are pre-sent to provide some idea of its systematicposition. It is a bothremydid because it has

    an exoccipital-quadrate contact and a fora-men stapedio-temporale not visible in dorsalview. The foramen stapedio-temporale is notvisible at all, but the dorsal surface of theprootic-quadrate suture is well enough pre-

    served to show that it is not present there andwas most likely on the anterior surface, as inother bothremydids.

    Within the Bothremydidae, Sankuchemyshas unique characters in common with theonly other Indian bothremydid known fromskulls, Kurmademys. Both taxa have an ex-tensively emarginated temporal roof withvery similarly shaped postorbitals, parietals,and squamosals, a condition so far unknownamong other bothremydids. At present, Sank-

    uchemys can best be hypothesized as a sistertaxon to Kurmademys within the Bothremy-didae.

    ACKNOWLEDGMENTS

    We thank our associates in pleurodiranstudies, P. Meylan and H. Tong, for their sup-port and counsel; Ed Heck did the photog-raphy and Alice Meredith Phillips did thedrawings. We appreciate the help of Judy

    Galkin in the preparation of the paper andthe care of the wildlife. We are grateful forthe help of our two anonymous reviewers,

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    Don Brinkman and Howard Hutchison, inimproving the quality of the paper.

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