A new species of the snake Madtsoia from the Upper Cretaceous of India and its paleobiogeographic...

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A new species of the snake Madtsoia from the Upper Cretaceous of Indiaand its paleobiogeographic implicationsDhananjay M. Mohabeya; Jason J. Headb; Jeffrey A. Wilsonc

a Palaeontology Division, Geological Survey of India (Central Region), Nagpur, India b Department ofBiology, University of Toronto at Mississauga, Mississauga, Ontario, Canada c Museum ofPaleontology and Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan,U.S.A.

Online publication date: 09 May 2011

To cite this Article Mohabey, Dhananjay M. , Head, Jason J. and Wilson, Jeffrey A.(2011) 'A new species of the snakeMadtsoia from the Upper Cretaceous of India and its paleobiogeographic implications', Journal of VertebratePaleontology, 31: 3, 588 — 595To link to this Article: DOI: 10.1080/02724634.2011.560220URL: http://dx.doi.org/10.1080/02724634.2011.560220

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Journal of Vertebrate Paleontology 31(3):588–595, May 2011© 2011 by the Society of Vertebrate Paleontology

ARTICLE

A NEW SPECIES OF THE SNAKE MADTSOIA FROM THE UPPER CRETACEOUS OF INDIAAND ITS PALEOBIOGEOGRAPHIC IMPLICATIONS

DHANANJAY M. MOHABEY,1 JASON J. HEAD,2

and JEFFREY A. WILSON*,3

1Geological Survey of India (Central Region), Palaeontology Division, Seminary Hills, Nagpur 440 006, India,[email protected];

2Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6,[email protected];

3Museum of Paleontology and Department of Geological Sciences, University of Michigan, 1109 Geddes Avenue, Ann Arbor,Michigan 48109-1079, U.S.A., [email protected]

ABSTRACT—We report the discovery of a new species of the snake Madtsoia from infratrappean horizons of Late Creta-ceous age in Pisdura, central India. Recovered vertebrae are large (1.83 cm long; 4.35 cm tall) and pertain to a snake that wasca. 5 m long. Discovery of Madtsoia in India extends the geographic distribution of the genus and represents only the secondspecies known from the Cretaceous. Vertebrae of Madtsoia pisdurensis sp. nov. are strikingly similar to those of M. bai and M.camposi (South America) and M. madagascariensis (Madagascar), but can be distinguished from them by a unique process onthe hemal keel, which is low, flat, and triangular in outline. Whereas the eastern Gondwanan species of Madtsoia (M. mada-gascariensis, M. pisdurensis) are Late Cretaceous in age, the western Gondwanan species (M. bai, M. camposi) are Paleogenein age. Geophysical evidence suggests that land connections between South America, Madagascar, and Indo-Pakistan weresevered by at least 100–90 Ma, which implies that Madtsoia achieved its broad geographic distribution either by (1) origin anddispersion before the end of the Turonian; or (2) the presence of an unrecognized land connection persisting into the latestCretaceous. Both hypotheses predict that Madtsoia will be discovered in Mesozoic strata of South America, where it survivedthe Cretaceous-Paleogene mass extinction.

INTRODUCTION

The earliest fossil records of snakes are Cretaceous in age andgeographically distinct. The record from Laurasian landmassesis very sparse and restricted to small-bodied, fossorial stem taxa(e.g., Rage, 1988; Gardner and Cifelli, 1999). In contrast, therecord from Gondwanan landmasses includes numerous crownand stem-group taxa preserved in depositional environments rep-resenting a wide range of habitats. These include Late Cretaceoussnakes from South America (e.g., Albino, 2000; Caldwell andAlbino, 2002; Apesteguıa and Zaher, 2006; Caldwell and Calvo,2008; Gomez et al., 2008), Afro-Arabia (e.g., Hoffstetter, 1959;Haas, 1979, 1980a, 1980b; Rage and Wouters, 1979; Werner andRage, 1994; Tchernov et al., 2000; Rage and Escuillie, 2003), andMadagascar (Hoffstetter, 1961a, 1961b; LaDuke et al., 2010).

The fossil snake clade Madtsoiidae has been recovered fromCretaceous deposits of South America, Africa, southern Europe,India, and Madagascar, and Cenozoic deposits of South America,Africa, Australia, and possibly North America (Andrews, 1901;Simpson, 1933; Hoffstetter, 1961a, 1961b; Rage et al., 2004; Folieand Codrea, 2005; Head and Holroyd, 2008). These occurrenceshave been hypothesized to represent a trans-Gondwanan faunaof large, terrestrial snakes that originated during the Cretaceousand survived until the Pleistocene (Scanlon and Lee, 2000). Thetiming of madtsoiid diversification and dispersion on Gondwananlandmasses is poorly constrained, however, due to uncertainty intheir phylogenetic interrelationships and limited sampling in crit-ical geographic regions, such as Indo-Pakistan.

Despite a long history of collecting fossil vertebrates in Creta-ceous deposits of Indo-Pakistan that extends back to the 1820s

*Corresponding author

(see Carrano et al., 2010), very few snake fossils have been re-ported from there compared to other Gondwanan landmasses.Those few Cretaceous snake remains that are known are smalland found predominantly in vertebrate microfossil assemblagesfrom ‘intertrappean’ sediments sandwiched between flows ofthe latest Cretaceous Deccan trap flood basalts of central In-dia (Prasad and Sahni, 1987; Rage and Prasad, 1992; Prasad andRage, 1995; Rage et al., 2004). More recent collections in the ‘in-fratrappean’ sediments below the Deccan Trap flood basalts inwestern India have produced larger and much more complete re-mains of the madtsoiid Sanajeh indicus (Mohabey, 1987; Wilsonet al., 2010) as well as a smaller-bodied form of uncertain affini-ties (Jain and Sahni, 1983). Here we describe a second, large-bodied (ca. 5 m long) madtsoiid from ‘infratrappean’ exposuresof the Lameta Formation of central India. This new snake is no-table for its large body size and close relationship to fossil snakesfrom Madagascar and South America, which provide evidence ofa trans-Gondwanan distribution of large-bodied Madtsoia duringthe Cretaceous and/or early Tertiary.

Institutional Abbreviations—AMNH, American Museum ofNatural History, New York; CGM, Cairo Geological Museum,Cairo; DGM, Museo de Divisao Geologia e Mineralogia deDepartamento Nacional de Producao Mineral, Rio de Janeiro;FMNH, Field Museum of Natural History, Chicago; GSI, Ge-ological Survey of India, Kolkata; UM, University of MichiganMuseum of Paleontology, Ann Arbor.

MATERIALS

The specimens are articulated and isolated vertebrae thatwere collected from two localities near the village of Pisdura in

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MOHABEY ET AL.—NEW MADTSOIA FROM INDIA 589

FIGURE 1. Map of India indicating study area in Maharashtra State(gray). The geological map at right is based on Mohabey and Samant(2005:fig. 1). Asterisk near village of Pisdura marks PIS 1, the holotypiclocality of Madtsoia pisdurensis. Political boundaries are approximate.

Maharashtra State, India, which we designate as PIS 1 and PIS 2(Fig. 1). Vertebrae from PIS 1 are slightly larger, lighter in color,and better preserved than those from PIS 2, which appear muchdarker in color due to hematitic staining. None of the vertebraefrom the latter locality are sufficiently preserved to be formallyreferred to the new species described in this paper, although theyare the appropriate size and general morphology for that species.High-resolution casts of holotype and best-preserved referredvertebrae are reposited at the University of Michigan Museumof Paleontology as UM 23496 (cast of 225/GSI/PAL/CR/10) and23497 (cast of 226/GSI/PAL/CR/10).

SYSTEMATIC PALEONTOLOGY

SERPENTES Linnaeus, 1758ALETHINOPHIDIA Nopcsa, 1923

MADTSOIIDAE Simpson, 1933MADTSOIA Simpson, 1933

MADTSOIA PISDURENSIS sp. nov.(Figs. 2–3)

Holotype—225/GSI/PAL/CR/10, two articulated posteriorprecloacal vertebrae from PIS 1 (Fig. 2; Table 1).

Referred Specimens—226/GSI/PAL/CR/10–231GSI/PAL/CR/10, 10 additional precloacal vertebrae, all but two of which werefound in articulated pairs, found within 10 m of the holotype at

PIS 1. These vertebrae are identical in size and morphologicallyindistinguishable from the holotype, and it is possible that theyrepresent the same individual.

Etymology—The specific name pisdurensis refers to Pisdura,the holotypic locality (ensis = place or locality; Latin).

Locality and Horizon—Localities PIS 1 and PIS 2, situated lessthan 1 km from the village of Pisdura (20◦21′N, 79◦2′E) in Ma-harashtra State, India, produced all known remains of Madtsoiapisdurensis. The outcrops at Pisdura are regarded as overbankdeposits of the Lameta Formation, Nand-Dongargaon Basin, andare located just north of the paleolake Dongargaon (Mohabeyand Samant, 2005). At Pisdura, fossilized remains are frequentlydisinterred by ploughing of the fields, a technique that affordsonly limited associations or geological context (e.g., Huene andMatley, 1933). The new snake is found in the same horizon andlocality that earlier yielded vertebrae of “Titanosaurus” blanfordi(Lydekker, 1877). The Lameta Formation is ascribed a Maas-trichtian age on the basis of microfossils (Salis and Saxena, 1998),magnetostratigraphy (Hansen et al., 2005), and its stratigraphicposition below the Deccan Trap flood basalts, the basal-most ofwhich have been have been dated at ca. 67.5 Ma (Courtillot et al.,1996; Keller et al., 2009).

Diagnosis—Large-bodied madtsoiid snake possessing a uniquehemal keel morphology on all mid- and posterior precloacal ver-tebrae that includes a posteriorly displaced, distinct process thatis triangular in ventral view, with a broad, flattened distal margin.

DESCRIPTION

The following description is based on the holotypic specimenof M. pisdurensis (225/GSI/PAL/CR/10); referred specimens dif-fer only in terms of preservation. Anatomical terminology fol-lows Head (2005). The holotype consists of two articulated pre-cloacal vertebrae that are nearly perfectly aligned. Comparisonof various views of the vertebrae shows that the zygapophysealcontacts are minimally offset (>2 mm) on right and left sides,and the vertebrae are aligned in neutral position (Fig. 2). Thevertebrae are in an excellent state of preservation, and all majormorphological features are preserved (Table 1). Minor damage ispresent on the ventral portion of the synapophyses on the left sideof both vertebrae, the right zygapophyses and right side of the zy-gosphene of the anterior vertebra, and the postzygapophyses andneural spine of the posterior vertebra. The holotypic and referredspecimens apparently reached skeletal maturity, because the ver-tebral sutures are completely closed. The holotypic vertebrae ofM. pisdurensis are 1.83 cm long (precondylar centrum length),which is approximately the same size as one of the largest spec-imens of M. madagascariensis (FMNH PR 2553; 1.81 cm long).That specimen of M. madagascariensis was estimated to repre-sent an animal approximately 5.1 m long (LaDuke et al., 2010);accordingly, we estimate that M. pisdurensis was ca. 5 m long.

The centra of M. pisdurensis are procoelous, with a well-defined, hemispherical condyle posteriorly and a correspondinglyconcave cotyle anteriorly. As in all snakes, the articular surfacesare inclined anteriorly such that the apices of the concavity andconvexity are anterodorsally shifted. Consequently, more of theposterior articular surface is visible in dorsal view, and moreof the anterior articular surface is visible in ventral view (Fig.2B, D). A well-defined paracotylar foramen is present adjacentto the dorsolateral quadrant of the right and left sides of thecotyle (Fig. 2A). The foramina are situated within fairly deepparacotylar fossae and separated from the neural canal by a shortstrut extending between the prezygapophysis and the cotyle. Thecentrum is subtriangular in ventral view, with the vertices formedby the condyle and the synapophyses. Wide, shallow subcentralfossae are present posteromedial to the synapophyses, and theirmedial margins form low, broad hemal keels that are separatedfrom the condyle by a well-defined groove that circumscibes


590 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 31, NO. 3, 2011

FIGURE 2. Madtsoia pisdurensis (225/GSI/PAL/CR/10). Half-tone drawings of the holotypic precloacal vertebrae in A, anterior, B, dorsal, C, pos-terior, D, ventral, and E, right lateral views. Abbreviations: con, condyle; cot, cotyle; f, foramen; fo, fossa; hp, hemal process; ir, interzygapophysealridge; nc, neural canal; nsp, neural spine; pct f, paracotylar foramen; poz, postzygapophysis; prz, prezygapophysis; pzgt f, parazygantral foramen; sr,subcentral ridge; st, zygapophyseal stop; syn, synapophysis; zgs, zygosphene; zgt, zygantrum. Scale bar equals 2 cm.



FIGURE 3. Geographic distribution of Madtsoia species shown on a latest Cretaceous (65 Ma) paleogeographic map (Mollweide projection; modifiedfrom Blakey, 2006). Vertebrae of M. bai (cast of AMNH 3155), M. madagascariensis (FMNH PR 2553), M. camposi (DGM 1310c; from Rage, 1998),and M. pisdurensis (225/GSI/PAL/CR/10) are shown in lateral and anterior views. Note that AMNH 3155 is a referred specimen that represents alarger individual than the holotype of M. bai (AMNH 3154). Vertebrae are scaled to same height. Scale bars equal 1 cm.

its articular surface (Fig. 2D). The hemal keels have distinctsubtriangular processes located just anterior to the condylethat are visible in ventral view. Hemal keels do not appearto be homologous to hypapophyses, which are formed fromfused intercentra in other squamates, and they are structurallydifferent from the elongate ventral processes generally termedhypapophyses in the anterior precloacal region of all snakes (e.g.,Hoffstetter and Gasc, 1969). The synapophyses are ellipticaland the parapophyseal and diapophyseal articular regions areslightly differentiated. The synapophyses are oriented 10–15◦

TABLE 1. Measurements (in mm) of the holotypic precloacal verte-brae of Madtsoia pisdurensis (225/GSI/PAL/CR/10).

Measurement Vertebra 1 Vertebra 2

Cotyle Height 16.3 —Width 16.9 —

Condyle Height — 13.7Width — 14.9

Synapophysis Height 17.6 (R) 16.9 (R)Width 10.0 (R) 10.0 (R)

Prezygapophysis Anteroposterior length 6.2 (R) —Transverse width 14.0 (R) —

Postzygapophysis Anteroposterior length — 5.7 (R)Transverse width — 10.5

∗(R)

Zygosphene Height 9.6 —Width 17.9 —

Zygantrum Height — 8.9Width — 18.8

Neural canal Height — 4.8Greatest width 10.0 9.8

Neural spine Anteroposterior length 8.9 —Height above zygosphene 14.3 —Width 3.5 —

vertebra Length (precondylar) 18.3 18.3Height 43.5 36.1

∗

Width acrosszygapophyses

41.2∗

42.6

Measurements of paired structures (e.g., synapophyses) were taken fromthe most completely preserved side (indicated in parentheses). An aster-isk (∗) indicates an incomplete measurement, a dash (—) indicates themeasurement could not be taken due to articulation of the elements.

from vertical in lateral view; they extend slightly beyond thecotyle ventrally and anteriorly but do not extend beyond theprezygapophyses laterally (Fig. 2C–E). The synapophyses con-nect to the cotyle, condyle, and zygapophyses via low ridgesthat together define shallow fossae. Two well-defined fossae arepresent dorsal and ventral to the synapophysis (Fig. 2D, E). Themore ventrally located subcentral fossa forms a gentle D-shape.It is defined by the ventral centrum and struts extending betweenthe synapophysis and cotyle, and the subcentral ridge betweensynapophysis and the condyle. The more dorsally locatedfossa is also D-shaped but smaller, defined by a strut betweenthe synapophysis and prezygapophysis, a strut between thesynapophysis and postzygapophysis, and the interzygapophysealridge. Small foramina open in the deepest parts of both dorsaland ventral fossae. The neural canal is trilobate (Fig. 2C), as it isin other large-bodied madtsoiids, boids, and pythonids.

The zygapophyses are subelliptical, with their long axesoriented transversely. The zygapophyseal contact is planar andinclined slightly dorsolaterally. The prezygapophyseal facetsare slightly broader anteroposteriorly than the postzygapophy-seal facets; immediately posterior to them is a well-markedledge that provided an anatomical stop for the precedingpostzygapophysis (Fig. 2B). The prezygapophyses are concaveanteriorly, with a subtle but consistent fossa visible in anteriorview (Fig. 2A). This fossa is positioned immediately posteriorto the strut connecting the synapophysis and postzygapophysison the preceding vertebra. The prezygapophyses are sepa-rated from the margin of the cotyle by a shallow trough thatforms the posterior margin of the fenestra through which thespinal nerve exited the vertebral column. The prezygapophyseslack the accessory processes present in alethinophidians andsome scolecophidians, and unlike other madtsoiids the prezy-gapophyses extend slightly beyond the lateral margins of thesynapophyses (Scanlon, 2006; Figs. 2A, 3). As mentioned above,the interzygapophyseal ridge connects the prezygapophysis andthe postzygapophysis. A shorter, arcuate strut extends betweenthe zygosphene and the dorsolateral corner of the zygantrum.In M. pisdurensis, as in M. madagascariensis, this arcuate strutdelineates a shallow fossa on the dorsolateral surface of theneural arch, just lateral to the neural spine (Fig. 2E). Thezygosphene bears articular facets that are slightly shorter than



TABLE 2. Valid species of Madtsoia.

Species Age Landmass Reference(s)

M. bai Eocene South America Simpson, 1933M. camposi Paleocene South America Rage, 1998M. madagascariensis Late Cretaceous (Maastrichtian) Madagascar Hoffstetter, 1961a; LaDuke et al., 2010M. pisdurensis Late Cretaceous (Maastrichtian) India This paper

those of the prezygapophyses. The zygosphene bears a gentle,rounded notch on its dorsal surface, near its junction with theneural spine, and its anterior surface is shallowly concave. Inlateral view (Fig. 2E), the articular facets of the zygosphene areovoid and dorsally oriented. A low ridge extends posterolaterallytowards the postzygapophysis from the back of the zygosphene,separating two shallow fossae that are visible in dorsal and lateralviews (Fig. 2B, D). The postzygapophyses are connected to theneural spine via posteriorly concave struts that form a medianembayment in dorsal view. These struts form the dorsolateralmargins of the zygantrum, which mirrors the shape of the zy-gosphene. Zygantral foramina open in the base of the zygantrumas well as in its anterior wall. Lateral to the zygantrum, largeparazygantral fossae are present approximately midway alongthe length of the articular facets. The fossae are distinct, andlarge parazygantral foramina are present within them (Fig. 2C).The neural spine originates anteriorly at the posterior marginof the zygosphene and posteriorly at the apex of the postero-median notch in the zygantrum. The neural spine is moderatelyelongate, transversely compressed, and inclined posteriorlyapproximately 35◦ from vertical. An available cross-section atits base is subtriangular; distally it is nearly elliptical in section(Fig. 2B).

PHYLOGENETIC AFFINITIES OF MADTSOIAPISDURENSIS

The majority of taxa referred to Madtsoiidae are representedonly by disarticulated and incomplete precloacal vertebrae (e.g.,Folie and Codrea, 2005), which limit the ability to corroboratethe monophyly of and interrelationships within the clade. Phylo-genetic analyses thus far have included only the three madtsoiidtaxa represented by cranial remains: Yurlunggur, Wonambi, andSanajeh (Scanlon, 2006; Wilson et al., 2010). The most thoroughdiagnosis of Madtsoiidae was provided by Scanlon (2006:S1),which listed eight vertebral features diagnosing Madtsoiidae:“. . .hypapophyses present only in anterior trunk; middle andposterior trunk vertebrae with moderately or well developedhaemal keel (except a few near the cloacal region), often withshort laterally paired projections on the posterior part of thekeel. All trunk and caudal vertebrae with a parazygantralforamen (or sometimes several foramina) in a more or lessdistinct fossa lateral to each zygantral facet; prezygapophysealprocesses absent; paracotylar foramina present; diapophysesrelatively wide, exceeding width across prezygapophyses at leastin posterior trunk vertebrae.”

This combination of characters may diagnose Madtsoiidae;individually, however, most characters are either symplesiomor-phies of Alethinophidia (e.g., absence of prezygapophysealprocesses), or are shared by members of more inclusive clades(e.g., well-developed hemal keels). For example, the most com-monly cited madtsoiid synapomorphy, presence of parazygantralforamina, also occurs variably in boid and pythonid taxa (Leeand Scanlon, 2002). Although presence of these characteristicsin other snakes does not rule them out as synapomorphies ofMadtsoiidae (or its subgroups), it underscores the importance ofidentifying new taxa on the basis of multiple diagnostic featuresand the utility of recognizing unique features of the group. One

such unique feature is the presence of a large parazygantralforamen located within a fossa, which we recognize as restrictedto the Cretaceous–Paleogene large-bodied taxa Madtsoia,Gigantophis, and possibly Wonambi and Yurlunggur.

Until now, the genus Madtsoia included three large-bodiedspecies (LaDuke et al., 2010). However, no autapomorphy-baseddiagnosis for the genus exists (e.g., Hoffstetter, 1961a), and thesingle-most rigorous study of madtsoiid postcranial morphologyprovides only a differential diagnosis of Madtsoia relative toother madtsoiids (LaDuke et al., 2010). Morphology of M. pis-durensis is consistent with the character delineation of Scanlon(2006) and LaDuke et al. (2010), and our comparisons of the In-dian specimens to the holotypic and referred remains of each ofthe three Madtsoia species did not identify significant differencesto justify separation at the generic level. Accordingly, we assignthe Indian species to Madtsoia (Table 2).

Character conflict among the four species of Madtsoia con-founds resolution of its interrelationships. Madtsoia pisduren-sis shares an anteroposteriorly narrow spinous process withM. bai and possibly M. camposi, but not M. madagascariensis(Simpson, 1933; Rage, 1998; LaDuke et al., 2010). Both M. pis-durensis and M. madagascariensis possess prezygapophyses thatextend as far or farther laterally than the synapophyses, whichis the plesiomorphic character state for madtsoiids (e.g., Scan-lon, 2006). Madtsoia bai shares the derived condition, laterallyextended synapophyses, with Wonambi, Gigantophis, Yurlung-gur, Sanajeh, and possibly M. camposi (Hoffstetter, 1961b; Smith,1976; Rage, 1998; Scanlon and Lee, 2000; Wilson et al., 2010). Thetriangular process on the hemal keel is unique to M. pisdurensis,and both M. bai and M. madagascariensis share bifid hemal pro-cesses with Wonambi and Yurlunggur. Madtsoia pisdurensis pos-sesses well-developed, deep parazygantral foramina, and sharesan anteroposterioly narrow and posteriorly angled spinous pro-cess with M. bai (Simpson, 1933) and Wonambi naracoortensis(Smith, 1976). It also shares large body size with M. bai, M.madagascariensis, and M. camposi (Simpson, 1933; Hoffstetter,1961a; Rage, 1998), Yurlunggur (Scanlon, 1992, 2006), and Won-ambi (Smith, 1976; Scanlon and Lee, 2000). The extremely largebody size of Gigantophis (precondylar centrum length = 3.06 cm;CGM 10022) exceeds estimates for all other madtsoiids (Headand Polly, 2004) and is here considered an autapomorphy of thegenus.

The close morphological similarity amongst the four Madtsoiaspecies suggests the genus is monophyletic, but diagnostic fea-tures are required to defend this claim adequately and assess theinterrelationships of its constituent species.

PALEOBIOGEOGRAPHIC IMPLICATIONS OFMADTSOIA PISDURENSIS

Four valid species of Madtsoia are currently recognized (Table2; Fig. 3): two are from South America (M. bai, M. camposi), athird is from Madagascar (M. madagascariensis), and a fourth isfrom India (M. pisdurensis). Madtsoia species have also been de-scribed from Spain (M. laurasiae; Rage, 1996, 1999) and Niger(Madtsoia aff. M. magascariensis; de Broin et al., 1974; Rage,1981), but their identity as Madtsoia species has recently beenchallenged by LaDuke et al. (2010), who referred M. laurasiae



to Menarana and relegated the Nigerian snake to ?Madtsoia.We treat both of these as distinct from Madtsoia. The presenceof Madtsoia in Madagascar, South America, and Indo-Pakistanimplies those landmasses had a biotic connection in the lateMesozoic or early Tertiary. However, as discussed above, itis possible that later-appearing large-bodied madtsoiids (i.e.,Gigantophis, Wonambi, Yurlunggur) also fall within the cladethat includes Madtsoia species. If this is the case (i.e., Madtsoiais paraphyletic), then biotic connections to Africa and Australiaare also implied. For the purposes of the discussion below, how-ever, we will consider only the simplest case—monophyly of thefour Madtsoia species—although we recognize that the paleobio-geographic pattern could be more complex.

The oldest pair of taxa, M. madagascariensis and M. pisduren-sis, are both Maastrichtian in age and provide an upper bound forwhen biotic connections might have been severed between Mada-gascar and Indo-Pakistan, respectively. The presence of youngerMadtsoia species in South America implies land connections withMadagascar and Indo-Pakistan that were severed sometime be-fore the Paleocene. Paleogeographers disagree on the nature andtiming of Gondwanan breakup, but most paleocoastline recon-structions place the breakup of Indo-Pakistan and Madagascar at100–90 Ma (e.g., Smith et al., 1994; Scotese, 2001, 2004). A laterbreakup at 80 Ma was hypothesized by Hay et al. (1999) basedlargely on the persistence of a land bridge formed by the Kergue-len Plateau, but this igneous province recently has been shown tohave had very limited subaerial exposure during the latest Creta-ceous (Ali and Aitchison, 2009).

There is a 25–30 million year discrepancy between estimatesof the loss of biotic connections between Indo-Pakistan, Mada-gascar, and South America implied by Madtsoia distribution(ca. 67.5 Ma) and the loss of those land connections impliedby geophysical evidence (ca. 100–90 Ma). There are threehypotheses relevant to this discrepancy. The most plausible arethat either (1) Madtsoia achieved its distribution prior to the lossof land connections among these landmasses, or that (2) therewas a dispersal corridor, currently unrecognized, connectingthese landmasses in the latest Cretaceous. The third hypothesis,that Madtsoia species dispersed across an oceanic barrier, seemsthe least likely because numerous other Indo-Pakistani taxa alsohave affinities elsewhere in Gondwana (e.g., Wilson et al. 2001,2003, 2009, 2010; Carrano and Sampson, 2008; Boyer et al., 2010;Prasad et al., 2010; Smith et al., 2010). The range of body sizeand dispersal potential of these taxa (i.e., snakes, notosuchians,theropods, sauropods, mammals) imply that they must havetaken advantage of a stable land corridor connecting theselandmasses rather than multiple sweepstakes dispersal events.

The first hypothesis, which postulates an early origin and dis-persion of Madtsoia, implies an unsampled history for the genusextending back to the middle of the Cretaceous on Madagascar,Indo-Pakistan, and South America. An early origin would alsoallow for Madtsoia-like forms to have reached other Gondwananlandmasses, such as Africa and Australia. There has been verylimited sampling of continental tetrapods on either Indo-Pakistanor Madagascar during this critical interval (i.e., 100–67.5 Ma),which is also the case for Africa and Australia, but South Amer-ica is well sampled. It is possible that Madtsoia has a more an-cient, but currently unsampled, history on Madagascar and Indo-Pakistan (as well as Africa and Australia), but its absence in theMesozoic of South America is less likely to be a sampling artifact.The early origin and dispersion resolution also implies a relativelyconservative axial morphology was retained in Madtsoia duringthe nearly 50 million years between its hypothesized origin 100Ma and its last appearance in the Casamayoran of Argentina ca.45–47 Ma (Carlini et al., 2005). There is already evidence Madt-soia axial morphology was fairly static between the Maastrichtianand the Casamayoran, so it may not be unreasonable to extendthis back to the mid-Cretaceous, especially given other examples

of conservative morphology in snakes (e.g., Szyndlar, 1991;Holman, 2000; see also Bell et al., 2010) and the possibility thatvariation was present in other parts of the skeleton, such as theskull.

The second resolution, the presence of a currently unrecog-nized dispersal corridor between South America, Madagascar,and Indo-Pakistan during the latest Cretaceous remains a vi-able explanation for this pattern and the pattern of other Indo-Pakistani terrestrial vertebrates. However, geophysical evidencefor any such corridor is currently lacking.

The stratigraphic range of Madtsoia spans the Cretaceous-Paleogene (K-Pg) boundary event, indicating that the genus sur-vived that mass extinction. It is not yet clear whether it survivedin India or Madagascar, but if our predicted timing of Madtsoiadispersal into South America is correct, then it clearly survivedthe K-Pg event there.

CONCLUSIONS

The discovery of a fourth species of the giant snake Madtsoia,M. pisdurensis, in the latest Cretaceous of India provides evi-dence of a trans-Gondwanan distribution of large-bodied madt-soiid snakes during the Cretaceous, which could be explained byearly origin and dispersion of the genus, or by a land corridorconnecting these landmasses in the latest Cretaceous. Based onour interpretation of its spatial and temporal distribution, Madt-soia is predicted to have survived the K-Pg event in South Amer-ica, but its survival in Madagascar and Indo-Pakistan is not yetknown. The occurrence of M. pisdurensis and M. madagascarien-sis in Indo-Pakistan and Madagascar, respectively, constrains theevolution of large body size in Madtsoia to no later than the sep-aration of the two landmasses at 100–90 Ma.

ACKNOWLEDGMENTS

This research was conducted under the auspices of a joint col-laboration between the Geological Survey of India, Ministry ofMines, and the University of Michigan. We thank Shri N. K.Dutta, Director General, GSI, Kolkata, and Shri K. K. K. Nair,Deputy Director General, GSI Central Region, Nagpur, for ex-cellent cooperation for carrying out joint study under the collab-orative program. We thank Kailash Ghodam, Shanan Peters, andMonica Wilson for field assistance in 2007. We thank C. Mehlingand D. Krause for access to collections in their care. Thanks to F.Carlini and D. Croft for assistance with age of the CasamayoranSALMA. B. Miljour prepared the halftone illustrations in Figure2 and prepared the map and edited the photos in Figure 3. Wethank J.-C. Rage and an anonymous reviewer for providing use-ful comments that improved the final version of the manuscript.J.-C. Rage is also thanked for permission to reproduce the im-ages of M. camposi that appear in Figure 3. Research was fundedby the National Geographic Society Committee for Research andExploration grant 8127-06 (to J.A.W.), the Geological Survey ofIndia (to D.M.M.), and an NSERC Discovery Grant (to J.J.H.).

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Submitted August 17, 2010; accepted January 28, 2011.Handling editor: Sean Modesto.


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