Tacuarembemys kusterae, gen. et sp. nov., a new Late Jurassic–?earliest Cretaceous continental...

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Tacuarembemys kusterae, gen. et sp. nov., a new LateJurassic–?earliest Cretaceous continental turtle fromwestern GondwanaDaniel Pereaa, Matías Sotoa, Juliana Sterlib, Valeria Mesaa, Pablo Toriñoa, Guillermo Rolanda

& Jorge Da Silvac

a Departamento de Evolución de Cuencas, Facultad de Ciencias, Universidad de la República.Iguá 4225, Montevideo, Uruguayb Museo Egidio Feruglio. Av. Fontana 140, 9100 Trelew, Chubut, Argentinac Museo de Geociencias de Tacuarembó. Gral. Artigas 191, Tacuarembó, UruguayPublished online: 04 Nov 2014.

To cite this article: Daniel Perea, Matías Soto, Juliana Sterli, Valeria Mesa, Pablo Toriño, Guillermo Roland & Jorge Da Silva(2014) Tacuarembemys kusterae, gen. et sp. nov., a new Late Jurassic–?earliest Cretaceous continental turtle from westernGondwana, Journal of Vertebrate Paleontology, 34:6, 1329-1341, DOI: 10.1080/02724634.2014.859620

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ARTICLE

TACUAREMBEMYS KUSTERAE, GEN. ET SP. NOV., A NEW LATE JURASSIC–?EARLIESTCRETACEOUS CONTINENTAL TURTLE FROMWESTERNGONDWANA

DANIEL PEREA,1 MAT�IAS SOTO,*,1 JULIANA STERLI,2 VALERIAMESA,1 PABLO TORIeNO,1

GUILLERMOROLAND,1 and JORGE DA SILVA3

1Departamento de Evoluci�on de Cuencas, Facultad de Ciencias, Universidad de la Rep�ublica. Igu�a 4225, Montevideo, Uruguay,[email protected]; [email protected]; [email protected]; [email protected]; [email protected];

2Museo Egidio Feruglio. Av. Fontana 140, 9100 Trelew, Chubut, Argentina, [email protected];3Museo de Geociencias de Tacuaremb�o. Gral. Artigas 191, Tacuaremb�o, Uruguay, [email protected]

ABSTRACT—A new continental turtle, Tacuarembemys kusterae, gen. et sp. nov., is described on the basis of a partialexternal mold of the carapace and associated shell bone fragments recovered from the Batov�ı Member (Late Jurassic–?earliest Cretaceous) of the Tacuaremb�o Formation, Paran�a Basin, Uruguay. The estimated length of the carapace is 18 cm.This new genus and species shows a unique combination of characters: a large nuchal notch, a pair of anterior supernumeraryscales, the absence of a cervical scale, and an external surface ornamentation that is macroscopically smooth with some thinlinear ridges perpendicular to the margins of the plates and microscopically composed of small, randomly distributed pits.The first two characters resemble those seen in the solemydid Naomichelys speciosa from the Cretaceous of North America,although the ornamentation is markedly different. Although this combination of characters—some shared with other taxa(including cryptodires and pleurodires) and some others that are autapomorphic—allows the recognition of a new genus andspecies, additional remains are yet needed in order to clarify its phylogenetic relationships. Tacuarembemys kusterae is partof the Priohybodus arambourgi Assemblage Zone, which is of Late Jurassic–?earliest Cretaceous age. This is the first turtleto be discovered in South American continental deposits of that age and thus increases the knowledge on the regionalevolution of Mesozoic turtles. The paleoenvironment for this species includes lakes and permanent and ephemeral rivers inarid-to-semiarid climatic conditions.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

INTRODUCTION

Although turtles from Upper Jurassic–Neocomian continentaldeposits are common in Asia, Europe, and North America (e.g.,Gaffney, 1979; Hirayama et al., 2000; Joyce, 2000; Sukhanov,2000; Milner, 2004; Rabi et al., 2010; Joyce et al., 2011; P�erez-Garc�ıa and Ortega, 2011), they are virtually unknown in Gond-wana. In South America, only the Early–Middle Jurassic Con-dorchelys antiqua Sterli, 2008, and an Aptian–Albian turtlefauna from Cerro Barcino, Argentina, and the Araripe Basin ofBrazil are known (Gaffney et al., 2006, 2007; de la Fuente et al.,2011; Sterli et al., 2013).Here we describe a new genus and species of turtle from the

Tacuaremb�o Formation (Late Jurassic–earliest Cretaceous),which represents the oldest known turtle from Uruguay. Further-more, this discovery begins to fill in the fossil record gap of conti-nental turtles from the Jurassic to the Cretaceous in SouthAmerica. Although the preserved remains of this new turtle arefragmentary, we considered that its significance regarding time,environment, anatomy, and taxonomy are worth exploring. Con-sequently, the main goals of this paper are to present, describe,and illustrate this new turtle, to explore its phylogenetic relation-ships in a global turtle data set, and to discuss the importance ofthis finding in the global context of turtle evolution.Institutional Abbreviations—FC-DPV, Colecci�on de Verte-

brados F�osiles, Facultad de Ciencias, Montevideo, Uruguay;

MGT, Museo de Geociencias de Tacuaremb�o, Tacuaremb�o,Uruguay.Anatomical Abbreviations—ASN, anterior supernumerary

scale; CB, cancellous bone; co, costal plate; EC, external cortex;IC, internal cortex; MA, marginal scale; ne, neural plate; nu,nuchal plate; pe, peripheral plate; PL, pleural scale; r, ridges(perpendicular to the plate margins); sf, possible Sharpey’sfibers; su, scale sulci; VE, vertebral scale.

GEOLOGIC SETTING

The sandstones that form the Tacuaremb�o Formation, whichcrops out in the southern region of the Paran�a Basin (called theNorte Basin in Uruguay), were first described by Walther (1911).Bossi (1966) gave formational rank to these sedimentary depos-its, and Bossi et al. (1975) further recognized lower and uppermembers. Perea et al. (2009) formalized this nomenclature bynaming them Batov�ı and Rivera members, respectively. Pereaet al. (2009) reviewed the paleontologic and chronostratigraphicknowledge of the Tacuaremb�o Formation, proposed a LateJurassic–Early Cretaceous age for it, and identified the Priohy-bodus arambourgi Assemblage Zone. Based on radiometricdates from the overlying basalts, the Tacuaremb�o Formationcannot be younger than the Hauterivian (Perea et al., 2001,2009, and references therein).Intensive field work carried out over the last couple of years in

the Batov�ı Member (the only fossiliferous member of the unit)yielded abundant body fossils of bivalves, gastropods, conchos-tracans, hybodontids, ‘semionotids,’ actinistians, dipnoans, croc-odyliforms, and theropod dinosaurs (see Perea et al., 2009).*Corresponding author.

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Moreover, ichnofossils attributed to sauropod dinosaurs havebeen described recently (Mesa and Perea, 2010). Of particularinterest are body fossils indicative of a Late Jurassic–Early Cre-taceous age (Perea et al., 2001; Shen et al., 2004; Soto and Perea,2008, 2010; Soto et al., 2012a, 2012b).One of the most recent discoveries in the Batov�ı Member is an

external partial mold of a carapace and associated shell bonefragments, described herein, that represent a new genus and spe-cies of turtle. The remains were recovered from fine-grained,pink-yellowish sandstones of mainly quartz composition. Biotur-bation is common in the vicinity of the outcrop.

MATERIALS ANDMETHODS

The specimen is housed in the MGT. A sandstone block con-taining the fossil was isolated from the rock and protected by aplaster jacket. Then, the mold was prepared under a binocularmicroscope and completely reinforced with cyanoacrylate. Acomputed tomography analysis was made so as to reject or con-firm the presence of bones potentially included in the sandstoneblock. Standard petrographic thin-sections of shell bone sampleswere prepared for histological analysis. The shell surface patternwas analyzed using a JSM-5900 LV scanning electron microscope(SEM). Taxonomic nomenclature in this paper follows Joyceet al. (2004), measurements and carapace terminology mainlyfollow Lyson et al. (2011), and histological terminology followsScheyer and Sander (2004) and Scheyer (2007). The stratigraphicframework follows Perea et al. (2009).The phylogenetic analysis is based on Sterli and de la Fuente

(2013). We added Tacuarembemys kusterae and a character(anterior supernumerary scale) to the Sterli and de la Fuente(2013) data set, resulting in an augmented data matrix of 102taxa and 241 characters, which was constructed in Mesquite(Appendix S1; Maddison and Maddison, 2007). All charactersshowing a clear morphocline were considered additive (22 intotal; see Appendix S2). All characters were weighted equally.All cladistic analyses were performed in TNT (Goloboff et al.,2008a, 2008b). Two rounds of tree bisection reconnection (TBR)were performed. In the first round, the original Wagner tree isreplicated and perturbed 1000 times using the TBR algorithm.All of the most parsimonious trees (MPTs) found in the firstround were subjected to a second round of TBR to find allMPTs. Consistency (CI) and retention (RI) indices were calcu-lated. Branch support is measured using Bremer support, jack-knife, and bootstrap resamplings. Jackknife and bootstrapresamplings were obtained after 1000 replicates, and the valuesare shown as the difference in the frequency of a clade and thefrequency when it is contradicted (GC values of Goloboff et al.,2003). If more than one MPT was found, a strict consensus wascalculated. If the strict consensus was highly collapsed, the scriptwritten by Pol and Escapa (2009) was run in TNT to identify the

rogue taxa and the precise causes (e.g., conflict of characters,lack of information, or both) for this behavior. To explore theevolution of certain characters, we mapped those charactersusing the TNT option of Optimize/Characters/Common map-ping. Character numbers as in TNT (i.e., starting from 0). InMesquite, character numbers are given as TNT number C1(i.e., starting from 1).

SYSTEMATIC PALEONTOLOGY

TESTUDINES Batsch, 1788, sensu Joyce, Parham, andGauthier, 2004

TACUAREMBEMYS, gen. nov.

Etymology—From Tacuaremb�o Province, the area where thespecimen was collected, and ‘emys,’ Greek for turtle.Type Species—Tacuarembemys kusterae, sp. nov.Diagnosis—As for type and only species.Distribution—Upper Jurassic–?lowermost Cretaceous,

Tacuaremb�o Province, northern Uruguay.

TACUAREMBEMYS KUSTERAE, sp. nov.(Figs. 2–6)

Etymology—AfterMrs. Selva Kuster, who found the specimen.Holotype—MGT-1185, which consists of an external partial

mold of carapace that preserves the morphology of some scales:vertebrals 1–3 and the anterior part of vertebral 4; marginals1–3; one pair of supernumerary anterior scutes; and medial por-tion of pleurals 1–3. It also preserves the morphology of someplates: the nuchal, peripherals 1–4 (partially), neurals 1–6, andcostals 1–5. Holotype also includes two partial costal plates, oneneural plate, and several shell bone fragments. Positive and neg-ative casts of the holotype are deposited at Facultad de Ciencias,Uruguay, as FC-DPV-2761.Type Locality and Horizon—Lane to Rinc�on de Giloca, 500 m

south of Road 26, Tacuaremb�o Province, Uruguay (Fig. 1).Batov�ı Member (Upper Jurassic–?lowermost Cretaceous) of theTacuaremb�o Formation.Diagnosis—Tacuarembemys kusterae differs from Con-

dorchelys antiqua Sterli, 2008, and Chubutemys copelloi Gaffney,Rich, Vickers-Rich, Constantine, Vacca, and Kool, 2007, in thesmaller size of the shell, type of ornamentation, having narrow ver-tebral scales, and having the sulcus between vertebrals 3 and 4 onneural 5. It also differs fromChubutemys copelloi in the absence ofpreneural bone and in the presence of anterior supernumeraryscales. It shares with Sinemydidae, crown Pleurodira, and crownCryptodira the presence of vertebrals narrower than pleural scalesand sulcus between vertebrals 3 and 4 placed on neural 5. It shareswith Araripemys barretoi Price, 1973, and Laganemys tenerensisSereno and ElShafie, 2013, the absence of cervical scale and the

FIGURE 1. Map showing the locality fromwhich MGT-1185, the holotype of Tacuarem-bemys kusterae, gen. et sp. nov., was collected.

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presence of a deep nuchal notch, allowing vertebral 1 reaching theanterior rim of the carapace; it differs from those taxa, however, inthe absence of highly ornamented shells, contact between neural 2and costal 3, the presence of anterior supernumerary scales, andthe shape of costal 1. It also differs fromA. barretoi in the shape ofthe nuchal and from L. tenerensis in the shape of peripherals. It isdifferent from Prochelidella cerrobarcinae in the presence ofnuchal notch, absence of cervical scale, presence of anterior super-numerary scale, and shape of vertebral 1. It differs from SinemyslensWiman, 1930, in the presence of marginal sulci on the periph-erals only (at least in the anterior region of the carapace) and inthe shape of the nuchal.Autapomorphic characters of Tacuarembemys kusterae

include carapace vaulted but not strongly convex, with awide and well-developed nuchal notch (length/width D 0.30);a pair of triangular anterior supernumerary scales placedbetween marginal 1, vertebral 1, and pleural 1; wide nuchalplate with curved anterior and posterior borders; and narrowneural plates, with neurals 1 and 3–6 hexagonal and neural 2rectangular in outline.

DESCRIPTION

The shell is represented by an external mold preserved in fine-grained sandstone, which reflects the morphology of the majorpart of the carapace (ca. two-thirds of it; see Fig. 2), as well asseveral disarticulated, mostly fragmentary carapace bones. Someof the most complete bones, such as costal 2 and neural 4(Fig. 3), match the correlated regions of the mold. The estimatedtotal shell length (straight sagittal length) is 180 mm (additionalmeasurements in Table 1). The mold preserves the limits ofscales and plates, but not the subtle shell surface ornamentation.This can be seen on the external surface of the bone fragmentsusing a stereoscopic lens or a microscope (see below). The por-tion of the carapace mold posterior to neural plate 6 and theexternal borders posterior to peripheral 2 are not preserved(Fig. 2). Contrary to other continental Jurassic turtles (e.g.,Kayentachelys aprix, Eileanchelys waldmani, Heckerochelysromani, xinjiangchelyids, sinemydids; Gaffney et al., 1987;Sukhanov, 2000, 2006; Matzke et al., 2004; Anquetin et al.,2009), the anterior border of Tacuarembemys kusterae is incisedby a pronounced and deep nuchal notch. The deep nuchal notchresembles the one observed in Mongolochelys efremovi from theUpper Cretaceous of Mongolia and Naomichelys speciosa fromthe mid-Upper Cretaceous of North America (Khozatsky, 1997;Hirayama et al., 2000).Macroscopically, the plates appear devoid of ornamenta-

tion (Figs. 3, 4A), except for small ridges that develop nearthe limits of the plates and are perpendicular to them. Theexternal surface of a costal plate fragment was examined andsmall, randomly distributed pits are observed both microscop-ically (Fig. 4A) and using the SEM (Fig. 5). In thin-section,small, randomly distributed vascular canals were observed(Fig. 6). Although the general morphology of T. kusteraeresembles that of N. speciosa, the lack of any remarkableornamentation in the former differs notably from the pustu-late ornamentation found in solemydids (Lapparent de Broinand Murelaga, 1999; Joyce et al., 2011).

Plates

The nuchal plate is arch-shaped and wider rather than long. Itsanterior margin is concave (due to a deep nuchal notch) and itsposterior margin convex. It articulates with the first neural plate,the first pair of costal plates, and the first pair of peripheralplates. Half of its lateral sutures are not clear, and perhaps they

were approximately coincident with the lateral borders of thefirst vertebral and first marginal scales.The neural series is preserved from neural 1 to neural 6. Neu-

ral 1 is hexagonal and contacts with the nuchal, costals 1 and 2,and neural 2. Neural 2 is the smallest of the preserved neuralsand is almost quadrangular, being slightly longer than wide. Itcontacts neurals 1 and 3 and costal 2 only. Neurals 3–6 are hexag-onal. All are in contact with the previous and following neuraland two costals (the corresponding costal and the anterior). Neu-rals 1 and 3–6 are subequal in size, with neural 3 slightly longerthan the remaining neurals. The morphology and contacts of theneural series of T. kusterae is similar to those of Siamochelys pen-insularis, a Middle Jurassic turtle from Thailand (Tong et al.,2002), but differ from those of stem turtles andN. speciosa (Gaff-ney et al., 1987; Hirayama et al., 2000).The first pair of costal plates is wing-shaped and contacts

peripherals 1–4. Costals 2–6 are roughly rectangular and much

TABLE 1. Selected measurements (in mm) of MGT-1185.

L 133W 133D 31NNL 16.5NNW 54WVE1 38.5LVE1 20.5WVE2 50.5LVE2 35.5WVE3 51LVE3 39WM1 12LM1 13WM2 14.5LM2 9.5WM3 16.5LM3 10.5Wnu 31.5Lnu 17.5Wco1 49.5Lco1 24Wco2 58Lco2 20Lco3 20Lco4 18.5Lco5 18.5Wne1 11Lne1 16.5Wne2 12Lne2 14.5Wne3 13Lne3 19.5Wne4 12Lne4 13Wne5 11Lne5 18Wpe1 23.5Lpe1 20.5LPL1 39

Abbreviations: D, maximum mold depth; L, maximummold length; LASN, maximum length of anterior super-numerary scale; Lco, maximum length of costal plate;LM, maximum length of marginal scale; Lne, maximumlength of neural plate; Lnu, maximum length of nuchalplate; Lpe, maximum length of peripheral plate; LPL,maximum length of pleural scale; LVE, maximum lengthof vertebral scale; W, maximum mold width (in straightline); WASN, maximum width of anterior supernumer-ary scale; Wco, maximum width of costal plate; WM,maximum width of marginal scale; Wne, maximumwidth of neural plate; Wnu, maximum width of nuchalplate; Wpe, maximum width of peripheral plate; WVE,maximum width of vertebral scale.

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wider than long. The contacts with the neurals are describedabove. Due to the preservation of the specimen, contacts amongcostals 2–6 with the peripherals are missing. The presence orabsence of costoperipheral fontanelles cannot be determined.Whereas most of the peripheral plates are quite poorly pre-

served, the anterior ones (1–4) can be reconstructed on the basis ofsome sutures and the anterior morphology of the first costal plate(Fig. 2).Peripheral 1 is part of the nuchal notch. It contacts with the

nuchal, costal 1, and peripheral 2. Peripheral 2 contacts withperipherals 1 and 3 and costal 1, whereas peripheral 3 contactswith peripherals 2 and 4 and costal 1. The shell bone fragments(thickness up to 5.25 mm) represent mostly carapace remains,including the left costal 2 and the neural 4, whereas a few othersprobably belong to the bridge region of the plastron.

Scales

The cervical scale is absent in T. kusterae, which seems to bedue to the deep nuchal notch and the short marginal scales. Thecervical scale has been lost independently in different clades ofturtles (e.g., pelomedusoids and testudinids). However, in a few(e.g., the pleurodiran turtle Araripemys barretoi from Aptian–Albian of Brazil; Meylan, 1996) the absence of the cervical scalecorrelates with the presence of a deep nuchal notch. In bothpelomedusoids and testudinids, the absence of the cervical scaleallows medial contact between the first marginals. This medialcontact is absent in T. kusterae and A. barretoi, where vertebral 1reaches the anterior border of the carapace at the level of thenuchal notch.Vertebral 1 is trapezoid and covers the major part of the

nuchal plate, the first half of neural 1, and part of costal 1. Verte-bral 1 is the narrowest of the preserved series. Vertebrals 2–4 ofT. kusterae are as wide as the pleurals (as in S. peninsularis andcrown Testudines), differing from the wide vertebrals of stemTestudines (e.g., Kayentachelys aprix, Condorchelys antiqua, andIndochelys spatulata) andN. speciosa (Gaffney et al., 1987; Dattaet al., 2000; Hirayama et al., 2000; Sterli, 2008). Vertebral 2 is

larger than the first, hexagonal, and broader than long. It coversthe posterior half of neurals 1 and 2, the anterior part of neural3, and parts of costals 1–3. Vertebral 3 is similar in shape andsize to the preceding vertebral; it includes posterior half of neu-rals 3 and 4, the anterior half of neural 5, and parts of costals 4–6.The contact between vertebrals 1 and 2, vertebrals 2 and 3, andvertebrals 3 and 4 is located in the first, third, and fifth neuralplates, respectively. The presence of the sulcus between verte-brals 3 and 4 and crossing neural 5 is also present in N. speciosaand crown Testudines. In some stem Testudines (e.g., K. aprix,I. spatulata, C. antiqua, and Eileanchelys waldmani), this sulcuscrosses neural 6 (Gaffney et al., 1987; Datta et al., 2000; Sterli,2008; Anquetin et al., 2009).A pair of subtriangular anterior supernumerary scales (sensu

Lyson et al., 2011) is placed between vertebral 1, pleural 1, andmarginal 1. We regard them neither as primarily homologous tothe supramarginal scales, which are present in large numbers insome stem Testudines (e.g., Proganochelys quenstedti and Pro-terochersis robusta; Joyce, 2007), nor to the supramarginalsfound in certain baenids along with anterior and posterior super-numerary scales (Brinkman and Nicholls, 1991; Lyson et al.,2011). A pair of anterior supernumerary scales was also docu-mented for N. speciosa, Boremys sp., Solnhofia parsonsi, and Ple-siochelys solodurensis, among others (Br€am, 1965; Hirayamaet al., 2000; Joyce, 2000; Lyson et al., 2011).Pleural scales are as wide as long, and they cover much of the

peripheral bones. Pleural 1 covers costals 1 and 2 and peripherals2–4. Pleural 2 covers part of costals 2–4, and pleural 3 covers partof costals 4–6. The sulci between pleurals 1 and 2, 2 and 3, and 3and 4 are located in costals 2, 4, and 6, respectively.The anterior marginal scales are entirely included in the

peripheral bones. Marginal scale 1 is small and roughly rectangu-lar in shape, making contact with vertebral 1, the anterior super-numerary scale, and marginal scale 2. Although the cervicalscale is absent, marginal scales do not contact each other in themidline, probably due to the deep nuchal notch present in T. kus-terae. The left (right in the mold) marginal 1 and part of the mar-ginals 2 and 3 are preserved, whereas the remaining marginal

FIGURE 2. MGT-1185, external mold of the carapace of Tacuarembemys kusterae, gen. et sp. nov.A, photograph of the specimen; B, reconstructionof the carapace. See text for anatomical abbreviations. Scale bar equals 50 mm.


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scales do not show their internal limits, nor do the pleural scalesshow their limits with them.

Plate Histology

Thin-sections of a costal plate allowed the assessment of thehistological structure of T. kusterae (Figs. 4B, 6). The platesshow a thick layer of cancellous bone framed by external andinternal cortices of compact bone.The external cortex is thick (thickness about 1.60 mm;

Figs. 4B, 6) and well vascularized with primary vascular canals,which are roughly perpendicular to the plate surface and seldombranching. The external end of these vascular canals could berelated to the pits observed in the SEM (Fig. 5). Conspicuousgrowth marks are not observed, although there may be a fewfaint ones. Possible Sharpey’s fibers can be observed (Fig. 6).

FIGURE 4. Binocular lens photographs of costal plates of Tacuarem-bemys kusterae, gen. et sp. nov. A, external ornamentation pattern of acostal plate; B, natural transverse section of a costal plate. See text foranatomical abbreviations. Scale bars equal 1 mm.

FIGURE 3. MGT-1185, shell bones of Tacuarembemys kusterae, gen. etsp. nov. A, B, paired neural plates; A, external and B, internal views. C,D, paired costal plate fragments; C, external and D, internal views. Seetext for anatomical abbreviations. Scale bars equal 10 mm.


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The cancellous bone is thick (thickness about 1.68 mm;Figs. 4B, 6) and strongly vascularized. Primary osteons withlamellae and bone cell lacunae are concentrically arranged andwidespread.

The internal cortex is thin (thickness about 0.88 mm;Figs. 4B, 6) and vascularized with scattered single primary vas-cular canals, and it is composed of parallel-fibered bone. Bonecell lacunae are arranged parallel to the plate surface. Theboundary between the cancellous bone and the internal cortexis sharply demarcated.

PHYLOGENETIC RESULTS

After two rounds of TBR, 240 most parsimonious trees(MPTs) of length 905 steps were found (Fig. S1), with a CI of0.335 and a RI of 0.763. A list of synapomorphies common to allMPTs is shown in Appendix S2. The strict consensus of all MPTs

FIGURE 6. Histological structure of Tacuarembemys kusterae, gen. etsp. nov., based on standard petrographic thin-sections of costal carapaceplates. See text for anatomical abbreviations. Scale bar equals 500 mm.

FIGURE 5. SEM micrograph showing the external ornamentation pat-tern of a costal plate of Tacuarembemys kusterae, gen. et sp. nov. A, gen-eral view; B, C, details of sectors highlighted in A. See text foranatomical abbreviations.


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shows a poorly resolved topology at the base of Testudines, butin all MPTs T. kusterae is recovered inside Testudines (Figs. S1,S2). A big polytomy could be caused by the absence of informa-tion or by a wildcard taxon (see below) jumping between differ-ent positions in the MPTs. Consequently, we ran the scriptwritten by Pol and Escapa (2009), which identified T. kusterae asthe most unstable taxon, jumping between two positions: (1) asthe sister taxon of crown Pleurodira and (2) as the sister clade ofSinemys lens (see reduced consensus in Fig. 7). Following thescript, contradictory characters do not cause the alternate posi-tion of T. kusterae and the scoring of several characters will helpto solve its phylogenetic position (see Fig. S3).

DISCUSSION

Phylogenetic Position of Tacuarembemys kusterae

Although Tacuarembemys kusterae behaves as a wildcardtaxon, the preserved characters allow us to place it insideTestudines. Testudines is supported in this analysis by twosynapomophies common to all MPTs: only one suprapygal

and small first thoracic rib, which are characters 136(0) and200(2), respectively. These two characters are not preservedin T. kusterae, but other scored characters preclude T. kus-terae from being a basal stem Testudines. The presence ofthe sulcus between vertebrals 3 and 4 on neural 5 (character142) is a synapomorphy of the clade crownward to Che-nyungchelys, whereas the presence of narrow vertebral scales(character 141) is a synapomorphy of the clade crownward toSiamochelys peninsularis. In stem Testudines (e.g., Kayen-tachelys aprix, Condorchelys antiqua, and Mongolochelys efre-movi), vertebral scales are wider than pleural scales and thesulcus between vertebrals 3 and 4 is located on neural 6. Theabsence of shell sculpturing (character 123) positions T. kus-terae in the clade crownward to Plesiochelys etalloni.Although only 7.5% (18 of 241 characters) of the charactersare known for T. kusterae, those characters support referralto Testudines. More specimens will hopefully bring moreinformation, in order to stabilize its phylogenetic positionamong Testudines and thus permit a better understanding ofthe evolution of this clade in Gondwana.

FIGURE 7. Simplified reduced strict consensus of 240 most parsimonious trees of length 905 steps showing the alternative position of Tacuarem-bemys kusterae (stars) inside crown Testudines. Black circle: synapomorphy based definition of Testudinata (see Joyce et al., 2004). Open circle: crowngroup definition of Testudines (see Joyce et al., 2004). Gray circles: clades discussed in the text.


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Character Evolution

MGT-1185 shows a combination of characters that are presentin a variety of turtles, but there is no other turtle that exhibits allof them together, which justifies the recognition of a new taxon.The characters discussed below are characters that have beenused for systematic purposes and that we consider worthdiscussing.Wide and Deep Nuchal Notch—Although several taxa belong-

ing to different clades show nuchal notches (Table 2, Fig. 8),only the cryptodiran Chitracephalus dumonii (Hauterivian–Aptian of Belgium and Spain; P�erez-Garc�ıa, 2012; Fig. 8A), thesolemydid Naomichelys speciosa (Aptian–Campanian of NorthAmerica; Hirayama et al., 2000; Joyce et al., 2011; Fig. 8B), andthe nanhsiungchelyids Nanhsiungchelys wuchingiensis and Zan-gerlia dzamunchondi (Upper Cretaceous of China and Mongolia,respectively; e.g., Sukhanov, 2000, and references therein;Fig. 8C) show a nuchal notch as pronounced as the one observedin Tacuarembemys kusterae (Fig. 8D). Other continental Jurassicturtles (e.g., Kayentachelys aprix, Heckerochelys romani, Indo-chelys spatulata, and Siamochelys peninsularis) have a straight ornearly straight anterior border of the carapace. Although thisfeature has been excluded from recent (including the present)cladistic analyses, it is worth exploring in future analyses (seevariation in Fig. S4).Ornamentation (Character 123)—The T. kusterae material

described does not show the diagnostic characters that wouldallow it to be reliably included in a specific clade within Tes-tudines. Although there are two characters shared with Nao-michelys speciosa, the ornamentation of the latter consists of“raised tubercles that easily dislocate from the surface”(Joyce et al., 2011:83), which is markedly different from thesmall pits observed in T. kusterae. Scale sulci are of differentshape as well (Hirayama et al., 2000:fig. 3). In our cladisticanalysis, the absence of evident shell sculpturing is synapo-mophy of the clade crownward from Plesiochelys etalloni (seeFig. S5).Absence of Cervical Scale (Character 137)—The absence of a

cervical scale is a characteristic of T. kusterae, but it is not the

only species in which this element has been lost (see Fig. S6).Although the cervical scale has been lost independently in sev-eral clades of turtles (e.g., pelomedusoids, testudinids, andSinemys sp.), the morphology resulting from that loss is not thesame in all cases. In testudinids and crown pelomedusoids, thecervical scale is absent but the anterior region of the carapace isnot notched, resulting in the medial contact of both first margin-als. In contrast, in T. kusterae, A. barretoi (Meylan, 1996;Fig. 8H), and Sinemys sp. (Brinkman and Peng, 1993), the ante-rior border is notched, the cervical is missing, but marginals 1make no contact at the midline.Anterior Supernumerary Scales (Character 138)—The pres-

ence of a pair of small, triangular anterior supernumerary scales,placed between marginal 1, vertebral 1, and pleural 1, is a rarefeature in turtles, but present in T. kusterae. Comparable scaleshave also been observed in the baenids Boremys pulchra and B.grandis (Brinkman and Nicholls, 1991; Lyson et al., 2011), Sty-giochelys sp. (Upper Cretaceous of North America; Brinkmanand Nicholls, 1991; Lyson et al., 2011), and Eubaena sp. (UpperCretaceous–Eocene of North America; Brinkman and Nicholls,1991; Lyson et al., 2011), in Plesiochelys solodurensis (LateJurassic of Europe; Br€am, 1965), and in the solemydid Nao-michelys speciosa (Hirayama et al., 2000: fig. 3; see Fig. 8G).Boremys pulchra additionally preserves supramarginal and pos-terior supernumerary scales (Brinkman and Nicholls, 1991;Lyson et al., 2011). In some taxa (e.g., Solnhofia parsonsi; Joyce,2000), there is only one (odd) supernumerary scale in the sameposition as the anterior supernumerary scale mentioned here.The presence of only one scale on one side of the shell isregarded as a shield abnormality (Zangerl, 1969; Pritchard,2007). On the contrary, the presence of paired (bilaterally sym-metric) anterior supernumerary scales seems to be relativelyconstant in some taxa (e.g., baenids) and seems not to be causedby shield abnormalities. The presence/absence of paired anteriorsupernumerary scales has been included in the present cladisticanalysis, which shows (see Fig. S7) that the presence of anteriorsupernumerary scales appeared independently several times dur-ing turtle evolution.

TABLE 2. Comparison of taxa with conspicuous nuchal notches.

Classification Taxon NNL/NNW Distribution Epoch

Xinjiangchelyidae Xinjiangchelys latimarginalis 0.17 China Middle JurassicXinjiangchelys tianshanensis 0.19 Kyrgyzstan Middle Jurassic (Cal)Annemys latiens 0.08 Mongolia Late Jurassic

Macrobaenidae Ordosemys leios 0.17* China Early Cretaceous?Adocidae (or Eucryptodira i.s.) Shachemys baibolatica 0.08 Uzbekistan Late Cretaceous (Tur–San)CryptodiraNanhsiungchelyidae Hanbogdemys orientalis 0.18 Mongolia Late Cretaceous (Tur–San)

Bulganemys jaganchobili 0.12 Mongolia Late Cretaceous (San)Zangerlia dzamynchondi 0.34 Mongolia Late Cretaceous (San)Nanhsiungchelys 0.29 China Late Cretaceous (Maa)Jiangxichelys ganzhouensis 0.24 China Late Cretaceous

Mongolochelyidae Mongolochelys efremovi 0.22 Mongolia Late Cretaceous (Maa)Lindholmemydidae Gravemys barsboldi 0.08 Mongolia Late Cretaceous (Maa)Solemydidae Naomichelys speciosa 0.34 U.S.A., Canada Early Cretaceous (Alb)

Solemys vermiculata 0.23 Spain Late Cretaceous (Cam)ParacryptodiraPleurosternidae ‘Glyptops’ typocardium 0.18 England Early Cretaceous (Ber)Cryptodira i.s. Chitracephalus dumonii 0.39 Spain, Belgium Early Cretaceous (Hau–Apt)PleurodiraBothremydidae Chupacabrachelys complexus 0.17 U.S.A. Late Cretaceous (Cam)Araripemydidae Araripemys barretoi 0.24 Brazil Early Cretaceous (Alb)Chelidae Yaminuechelys maior 0.23 Argentina Cenozoic (Pal)Testudines i.s. Tacuarembemys kusteri, gen. and sp. nov. 0.30 Uruguay Late Jurassic–?earliest Cretaceous

Nuchal notch length/nuchal notch width measured from Meylan and Gaffney (1991), Lapparent de Broin and Murelaga (1999), Hirayama et al.(2000), Sukhanov (2000), Milner (2004), Bona and de la Fuente (2005), Lehman andWick (2010), Tong and Mo (2010), and P�erez-Garc�ıa (2012). Esti-mated measurements indicated with *.Abbreviations: Alb, Albian;Apt, Aptian; Ber, Berriasian; Cal, Callovian; Cam, Campanian;Hau, Hauterivian;Maa, Maastrichtian; NNL, Nuchal notch length;NNW, Nuchal notch width; Pal, Paleocene; San, Santonian; Tur, Turonian.


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Vertebral/Pleural Scale Relationships (Character 141)—Thepresence of vertebral scales 2–4 that are wider than pleural scalesis well known to be plesiomorphic for Testudines because it ispresent in basal turtles such as Proganochelys quenstedti, K.aprix, I. spatulata, and Condorchelys antiqua (Gaffney et al.,1987; Gaffney, 1990; Datta et al., 2000; Hirayama et al., 2000;Sterli, 2008). Contrary to the condition present in basal turtles,T. kusterae has narrow vertebral scales (condition present crown-ward to Chengyunchelys; see Fig. S8).Sulcus Between Vertebrals 3 and 4 (Character 142)—In stem

turtles such as K. aprix, C. antiqua, and Eileanchelys waldmani(Gaffney et al., 1987; Sterli, 2008; Anquetin et al., 2009), thesulcus between vertebrals 3 and 4 is located on neural 6. In con-trast, the sulcus between vertebrals 3 and 4 crosses neural 5in crown Testudines, N. speciosa (Fig. 9G), and T. kusterae(Hirayama et al., 2000; Sterli and de la Fuente, 2013). This char-acter was recovered in the present cladistic analysis as synapo-morphic for the clade crownward to Siamochelys peninsularis(see Fig. S9).

Paleoecology

Histology can help infer the degree of aquatic adaptation inrecent and fossil turtles (e.g., Ernst et al., 2006; Scheyer, 2007).Four categories were recognized by Scheyer (2007): I (terrestrialturtles), II (semiaquatic and mainly aquatic), III (fully aquatic),and IV (extreme adaptation to marine/aquatic environments).Plates of Tacuarembemys kusterae show a diploe structure(external cortex, cancellous bone, and internal cortex) that isindicative of categories I and II. The internal cortex is reduced inthickness, as in categories II and III. However, it represents half

the thickness of the external cortex; i.e., disparity is not as greatas in turtles of categories III and IV. Thus, this turtle is morelikely to belong to category II (semiaquatic and mainly aquatic).Further evidence for the aquatic lifestyle is that the shell isdorsoventrally low; i.e., not strongly convex (e.g., see Sukhanov,2000). All the preceding evidence agrees with the paleoenviron-ment proposed for the Tacuaremb�o Formation: permanent andtemporary streams and lakes (Perea et al., 2001, 2009). However,doubts have been cast concerning the reliability of several meanstraditionally used to infer extinct turtle paleoecology (Bensonet al., 2011).Given the absence of cranial remains, nothing can be inferred

about diet. If T. kusterae was durophagous, potential prey wouldhave included some of the aquatic invertebrates (e.g., bivalvesand gastropods) also found in the Batov�ı Member (see Mart�ınezet al., 1993; Mart�ınez and Figueiras, 1993; Shen et al., 2004).Abundant mollusk molds have been found close to the typelocality.

The Continental Jurassic–Early Cretaceous Fossil Recordof South American Turtles

Until the Middle Jurassic, the worldwide turtle record wasdominated by stem Testudines of cosmopolitan distributionacross Pangaea (e.g., Kayentachelys aprix, Condorchelys antiqua,Indochelys spatulata, Heckerochelys romani, and Eileanchelyswaldmani). In accordance with the breakup of continental land-masses, the paleobiogeography of turtles increased in complex-ity, and the cosmopolitan distribution that had been dominantuntil the Middle Jurassic was replaced with Laurasian and Gond-wanan distributions. Moreover, between the Middle Jurassic and

FIGURE 8. Carapaces of turtles with well-developed nuchal notches (not to scale). A, Chitracephalus dumonii (re-drawn from P�erez-Garc�ıa, 2012);B, Naomichelys speciosa (redrawn from Hirayama et al., 2000); C, Zangerlia dzamunchondi (redrawn from Sukhanov, 2000);D, Tacuarembemys kus-terae (this work); E, Mongolochelys efremovi (redrawn from Sukhanov, 2000); F, Solemys vermiculata (redrawn from Lapparent de Broin and Mure-laga, 1999); G, Jiangxichelys ganzhouensis (redrawn from Tong and Mo, 2010); H, Araripemys barretoi (re-drawn from Meylan and Gaffney, 1991).Thin lines represent sutures; thick lines represent sulci.


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FIGURE 9. Distribution of Late Jurassic and earliest Cretaceous turtle taxa discussed in the text.A, Oxfordian–Tithonian; B, Berriasian–Barremian.Based mainly on Hirayama et al. (2000), Lapparent de Broin (2000), and Sukhanov (2000). Paleogeographic maps after Ronald Blakey, Colorado Pla-teau Geosystems.


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Late Jurassic, several (extant and extinct) clades originatedand diversified (e.g., Cryptodira, Pleurodira, and Meiolani-formes; Sterli et al., 2012). However, Upper Jurassic conti-nental deposits with vertebrates are scarce in Gondwana, andparticularly in South America (Fig. 9A). For all of theabove-mentioned reasons, this new turtle from Uruguay,though fragmentary, preserves valuable information from akey time in turtle evolution.The components of the continental Upper Jurassic and

Lower Cretaceous record of turtles in Gondwana and Laura-sia are notably different from one another. The Upper Juras-sic record of continental turtles of Gondwana is virtuallynonexistent, because the Ca~nad�on Asfalto Formation (whereCondorchelys antiqua Sterli, 2008, was found) has recentlybeen radiometrically dated as Early–Middle Jurassic (C�uneoand Bowring, 2010). Fragmentary turtle remains from theUpper Jurassic of Ethiopia (labeled ‘Testudinata indet.’ inFig. 9A) have been reported by Goodwin et al. (1999). If theproposed affinities with pelomedusids, plesiochelyids, and/orsolemydids (termed ‘pleurosternids’ by Goodwin et al., 1999)is confirmed, it would provide interesting paleobiogeographicimplications. On the contrary, a large number of Early Creta-ceous taxa have been described from Gondwana. The oldestrecords of identified Cretaceous continental turtles fromGondwana come from the Barremian of Brazil (Gallo et al.,2009) and Morocco (Lapparent de Broin, 2000), the Aptian–Albian of Argentina (de la Fuente et al., 2007, 2011; Gaffneyet al., 2007), and the Albian of Australia (Gaffney et al.,1998; Smith, 2010; Smith and Kear, 2013). Early Cretaceouschelonian faunas from Africa were dominated by panpelome-dusoid pleurodiran turtles (Lapparent de Broin, 2000),Recent taxa of which are restricted to South America andAfrica (Bonin et al., 2006). In contrast, the Early Cretaceouschelonians from continental South America and Australiawere dominated by the extinct meiolaniforms (Gaffney et al.,2007; Smith and Kear, 2013) and by panchelid pleurodiranturtles (de la Fuente et al., 2007, 2011; Smith, 2010), of whichthe latter are now restricted to South America and Austral-asia (Bonin et al., 2006). The list of Early Cretaceous SouthAmerican turtles is completed with the Aptian–Albian San-tana fossils. However, the paleoenvironment of the Araripebasin is still debated due to the existence of both freshwaterand saline deposits (Gaffney et al., 2006).The Late Jurassic and Early Cretaceous continental turtle

fauna from Laurasia was very different from that found inGondwana (Fig. 9). Contrary to Gondwana, in Laurasia thereis no evidence of the presence of crown Pleurodira and/orMeiolaniformes in the Upper Jurassic to Early Cretaceous.Besides, most of the components of the Early Cretaceous con-tinental turtle fauna from Laurasia were already present fromthe Late Jurassic. That was not the case in Gondwana, possi-bly because of the scarcity of Upper Jurassic continentaldeposits. Continental environments from North America andEurope were dominated by pleurosternids, ‘macrobaenids,’and solemydids (Gaffney, 1979; Brinkman et al., 2000; Joyceet al., 2011; P�erez-Garc�ıa and Ortega, 2011). A different sce-nario occurred in Asia, where one of the most diverse recordsof Late Jurassic to Early Cretaceous turtles can be found(Fig. 9). The Asian record was dominated by‘xinjiangchelyids,’ ‘sinemydids,’ sinochelyids, pantrionychians,pantestudinoids, and the stem-testudine Sichuanchelys sp.(Sukhanov, 2000, and references therein; Danilov and Parham,2007; Rabi et al., 2010, and references therein). In the presentcladistic analysis, T. kusterae behaves as a wildcard taxon, andone of its alternative positions is as a sister clade of Sinemyslens. We are cautious in recognizing this position, and we pre-fer to wait for more complete specimens before regarding T.kusterae as a sinemydid.

ACKNOWLEDGMENTS

We thank V. Tonto Mu~noz and M. Garc�ıa Fontes for theirvaluable help in the computer tomography analysis. T. M.Scheyer is acknowledged for helpful comments. X. Murelaga, A.P�erez-Garc�ıa, and F. Montenegro provided important referen-ces. J. Gonz�alez made the drawings from Figures 2, 3, and 9. Weare indebted to the authors and editors who provided permissionfor the redrawing of the figures that compose Figure 9. Carefulreviews by two anonymous reviewers greatly improved an origi-nal draft of the manuscript. This work was partially supported byCSIC/UdelaR-C028-348/2011 and ANII/FCE-2007-110.

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Submitted April 22, 2013; revisions received October 14, 2013;accepted October 22, 2013.Handling editor: Sean Modesto.


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