A definitive abelisaurid theropod dinosaur from the early Late Cretaceous of Patagonia

58

Journal of Vertebrate Paleontology 22(1):58–69, March 2002q 2002 by the Society of Vertebrate Paleontology

A DEFINITIVE ABELISAURID THEROPOD DINOSAUR FROM THE EARLY LATECRETACEOUS OF PATAGONIA

MATTHEW C. LAMANNA1, RUBEN D. MARTINEZ2, and JOSHUA B. SMITH1

1Department of Earth and Environmental Science, University of Pennsylvania, 240 South 33rd Street, Philadelphia,Pennsylvania 19104-6316, USA, [email protected];

2Laboratorio de Paleovertebrados, Universidad Nacional de la Patagonia ‘‘San Juan Bosco’’, C. C. 360 (9000), ComodoroRivadavia, Argentina

ABSTRACT—A nearly complete, well-preserved maxilla of an abelisaurid theropod from the early Late Cretaceous(middle Cenomanian-Turonian) Lower Member of the Bajo Barreal Formation of Chubut, Argentina represents the firstdefinitive member of the abelisaurid clade from pre-Senonian (Coniacian–Maastrichtian) deposits. The new maxillashares derived characters with the maxillae of Carnotaurus and Majungatholus, and with AMNH 1955, a maxillapreviously referred to Indosuchus, suggesting that it pertains to the abelisaurid subclade Carnotaurinae. Abelisaurusshares apomorphic characters with Carnotaurinae, but many of these characters are also found in the carcharodonto-saurid allosauroid Giganotosaurus. As it is known only from cranial material lacking carnotaurine synapomorphies,Abelisaurus may represent a late-surviving carcharodontosaurid derivative.

The presence of the Bajo Barreal predator in the early Late Cretaceous indicates that the origin of Abelisauridaehad occurred by then. The occurrence of the new maxilla is nearly concurrent with the accepted interval of tectonicdivergence between South America and Africa. Its discovery thus weakens support for the recent hypothesis that theabelisaurid clade could not have penetrated Africa. The known occurrence of Abelisauridae may reflect a former pan-Gondwanan distribution, and is thus of limited utility in the support of Late Cretaceous paleogeographic hypotheses.

RESUMEN.—Un maxilar casi completo y bien preservado de un teropodo abelisaurido del Cretacico Tardıo temprano(Cenomaniano medio–Turoniano), proveniente del Miembro Inferior de la Formacion Bajo Barreal de Chubut, Argen-tina representa el primer miembro definitivo del clado abelisaurido de depositos pre-Senonianos (Coniaciano–Maas-trichtiano). El nuevo maxilar comparte caracteres derivados con los maxilares de Carnotaurus y Majungatholus, y conAMNH 1955, un maxilar referido previamente a Indosuchus, sugiriendo que este pertenece al subclado abelisauridoCarnotaurinae. Abelisaurus comparte caracteres apomorficos con Carnotaurinae, pero muchos de estos caracteres seencuentran tambien en el carcharodontosaurido allosauroide Giganotosaurus. Como es conocido solo por materialcraneano, careciendo de sinapomorfıas carnotaurinas, Abelisaurus puede representar un sobreviviente tardıo de uncarcharodontosaurido derivado.

La presencia del predador de Bajo Barreal en el Cretacico Tardıo temprano indica que el origen de Abelisauridaeha ocurrido en ese momento. La aparicion del nuevo maxilar es casi concurrente con el intervalo aceptado de diver-gencia tectonica entre Sudamerica y Africa. De este modo este descubrimiento debilita el sosten de la reciente hipotesisde que el clado abelisaurido no habrıa penetrado Africa. La conocida presencia de Abelisauridae puede reflejar unaantigua distribucion pan-Gondwanica, siendo ası de limitada utilidad en el sosten de las hipotesis paleogeograficas parael Cretacico Tardıo.

INTRODUCTION

The past two decades have produced well-preserved speci-mens of several new or previously poorly known Cretaceouspredatory dinosaurs (theropods) from areas that comprised thesouthern supercontinent of Gondwana. Exceptional finds havebeen made on many now disparate Gondwanan landmasses, in-cluding South America (Bonaparte, 1985, 1991a, 1996; Bona-parte and Novas, 1985; Martınez et al., 1986; Bonaparte et al.,1990; Coria and Salgado, 1995; Novas, 1997a, 1998; Novasand Puerta, 1997; Coria and Currie, 1997; Martınez and Novas,1997; Coria and Salgado, 1998; Martınez et al., 1999; Coria etal., 2000), Africa (Sereno et al., 1994, 1996, 1998; Russell,1996; Taquet and Russell, 1998; De Klerk et al., 2000; Laman-na et al., 2000), India (Chatterjee and Rudra, 1996), and Mad-agascar (Sampson et al., 1998, 2000). These finds have greatlyadded to knowledge of the evolution of Southern Hemispheretheropods, and have led to the recognition of several previouslyunknown predatory clades. The spatial and temporal distribu-tion of these clades has been used to support biogeographichypotheses or to test various tectonic schemes pertaining toCretaceous Gondwanan fragmentation (e.g., Bonaparte, 1986;

Sereno et al., 1994, 1996; Sampson et al., 1998). However, asfundamental questions remain concerning theropod evolutionon southern continents, these hypotheses are problematic. Onecrucial limiting factor has been poor knowledge of the timeintervals in which Gondwanan theropod clades appeared.

The abelisaurids are arguably the most distinctive of theSouthern Hemisphere predatory dinosaurs (e.g., Bonaparte,1986, 1991b). Sereno (1998) and Padian et al. (1999) defineAbelisauridae as all descendants of the most recent commonancestor of Abelisaurus and Carnotaurus. The existence of theclade in several Gondwanan landmasses is well-documented,with the identification of Abelisaurus comahuensis (Bonaparteand Novas, 1985), Carnotaurus sastrei (Bonaparte, 1985), anda new genus (Coria et al., 2000) from Argentina, Indosuchusraptorius and Indosaurus matleyi (Huene and Matley, 1933)from India, and Majungatholus atopus (Sues and Taquet, 1979;Sampson et al., 1998) from Madagascar. Putative abelisauridshave been reported from the Late Cretaceous of Europe (Buf-fetaut et al., 1988; Buffetaut, 1989; Astibia et al., 1990; Le-Loeuff and Buffetaut, 1991) and the early Late Cretaceous ofSouth America (Martınez et al., 1986) and Africa (Russell,1996), but these records have been strongly challenged (Coria

59LAMANNA ET AL.—EARLY ABELISAURID

FIGURE 1. Geographic location and geologic context of the new abe-lisaurid maxilla (UNPSJB-PV247), after Martınez et al. (1986). Thespecimen was obtained from the Lower Member of the early Late Cre-taceous (middle Cenomanian–Coniacian) Bajo Barreal Formation, westof Lago Musters, Estancia ‘‘Ocho Hermanos,’’ Chubut Province, Ar-gentina.

and Rodriguez, 1993; Coria and Salgado, 1998; Sampson et al.,1998). Definitive abelisaurids are known only from the Seno-nian (Coniacian–Maastrichtian) of South America, India, andMadagascar (Ardolino and Delpino, 1987; Sampson et al.,1998; Forster, 1999). The biogeographic and temporal distri-bution of the clade has recently been cited as evidence in sup-port of Late Cretaceous terrestrial vertebrate dispersal betweenSouth America and India-Madagascar (Sampson et al., 1998).Contrary to most current paleogeographic scenarios (e.g., Sco-tese and Golonka, 1993; Smith et al., 1995; Roeser et al., 1996;Scotese, 1997), but consistent with the work of Hay et al.(1999), this hypothesis assumes ‘‘land bridges’’ between theseareas persisting well into the Late Cretaceous. Recent hypoth-eses of abelisaurid biogeography by Sampson et al. (1998) alsopresume that abelisaurid origins occurred subsequent to the tec-tonic separation of South America and Africa, preventing theclade from dispersing to the latter.

Martınez et al. (1993) briefly reported an abelisaurid maxillafrom the pre-Senonian Lower Member of the Bajo Barreal For-mation of central Patagonia. The early occurrence of the spec-imen strengthens questions concerning the aforementioned hy-potheses and the utility of the abelisaurid clade as a proxy forLate Cretaceous paleogeographic reconstruction.

Institutional Abbreviations AMNH, American Museumof Natural History, New York; FMNH, Field Museum of Nat-ural History, Chicago; GSI, Geological Survey of India, IndianMuseum, Calcutta; MACN, Museo Argentino de Ciencias Na-turales, Buenos Aires; MC, Museo Provincial de Cipolletti, RıoNegro, Argentina; MWC, Museum of Western Colorado, GrandJunction; NCSM, North Carolina State University Museum,Raleigh; PVL, Fundacıon-Instituto Miguel Lillo, Tucuman, Ar-gentina; UMNH, Utah Museum of Natural History, Salt LakeCity; UNPSJB, Universidad Nacional de Patagonia ‘‘San JuanBosco,’’ Comodoro Rivadavia, Argentina; USNM, NationalMuseum of Natural History, Washington D. C.

Anatomical Abbreviations aof, antorbital fossa; aofe, an-torbital fenestra; d, depression at base of rostromedial process;df, dental foramina; idp, interdental plates; ll, lamina lateralisof ascending ramus; lm, lamina medialis of ascending ramus;ls, lateral sculpture; mx, maxillary tooth position; pf, proma-xillary fenestra; rp, rostromedial process; rr, rostral ramus; tm,torus maxillaris.

SYSTEMATIC PALEONTOLOGY

THEROPODA Marsh, 1881NEOCERATOSAURIA Novas, 1991

ABELISAURIA Novas, 1992ABELISAUROIDEA Bonaparte, 1991b

ABELISAURIDAE Bonaparte and Novas, 1985CARNOTAURINAE Sereno, 1998 gen. et sp. indet.

Material UNPSJB-PV247, a nearly complete left maxilla,missing only the most dorsal portion of the ascending ramusand several tooth crowns.

Locality Estancia ‘‘Ocho Hermanos,’’ Sierra de San Ber-nardo, Chubut Province, Patagonia, Argentina (Fig. 1).

Horizon and Age Lower Member of the Bajo Barreal For-mation (Upper Cretaceous: middle Cenomanian-Turonian). TheBajo Barreal is part of the Chubut Group, stratigraphically over-lying the Castillo Formation and overlain by the Laguna Pala-cios Formation. At the ‘‘Ocho Hermanos’’ locality, the BajoBarreal is 255 m thick, with the Lower Member (148 m) some-what thicker here than the Upper Member (107 m). UNPSJB-PV247 was recovered from strata high within the Lower Mem-ber, approaching the contact between the two members (Fig. 1).

The Bajo Barreal Formation has traditionally been regardedas Senonian (Coniacian–Maastrichtian) in age (e.g., Huene,1929; Bonaparte and Gasparini, 1979). However, the palynol-

ogy of a subsurface equivalent of the Bajo Barreal, the CaletaOlivia Member of the Canadon Seco Formation, suggests a lateAlbian-Cenomanian age (Archangelsky et al., 1994). Moreover,palynomorph assemblages indicate an Albian-early Cenoma-nian age for the Huincul Formation of Neuquen Province (Va-llati, 1998); the underlying Candeleros Formation is thereforeolder. The Bajo Barreal Formation shares two sauropod generawith the Candeleros, suggesting that both units were depositednearly simultaneously (Sciutto and Martınez, 1997). Finally, re-cently reported Ar-Ar ages for the Bajo Barreal range from 95.8to 91.0 Ma, corresponding to the middle Cenomanian-late Tu-ronian (Gradstein et al., 1995, 1997; Bridge et al., 2000). Col-lectively, the data indicate a middle Cenomanian–early Conia-cian age (96.0–88.5 Ma) for the Bajo Barreal Formation(Bridge et al., 2000). The stratigraphic position of UNPSJB-PV247 indicates a late Cenomanian–early Turonian age.

The Bajo Barreal is lithologically dominated by mudstoneand sandstone, with abundant volcaniclastic sediment. The stra-ta are fluvial and lacustrine, with general sediment dispersal tothe east. More detailed reconstructions of depositional environ-ment differ in several regards (see Bridge et al., 2000, and ref-erences therein).

60 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 22, NO. 1, 2002

TABLE 1. Tetrapod fauna of the Bajo Barreal Formation.

CheloniaChelidae indet. (2 species) (Broin and Fuente, 1993)

Crocodyliformes indet. (Martınez et al., 1986)Dinosauria

TheropodaTheropoda incertae sedis

gen. et sp. indet. (Martınez et al., 1999)Neoceratosauria incertae sedis

Xenotarsosaurus bonapartei (Martınez et al., 1986)Abelisauridae

Carnotaurinaegen. et sp. indet. (Martınez et al., 1993; this paper)

?Coelurosauriagen. et sp. nov. A (Martınez and Novas, 1997)

SauropodaSauropoda indet. (Powell et al., 1989; Sciutto and Martınez,

1994)Neosauropoda

Diplodocoidea indet. (Sciutto and Martınez, 1994; Martınez,1998c)

Titanosauriformesgen. et sp. nov. B (Martınez, 1998b, 1999)Titanosauria

?Andesaurus sp. (Sciutto and Martınez, 1997)Titanosauridae

Titanosauridae indet. (Powell et al., 1989; 5Antarctosaurus wichmannianus, Laplatasaurus sp.,

Weishampel, 1990; Sciutto and Martınez, 1994)Epachthosaurus sciuttoi (Powell, 1990)?Argyrosaurus superbus (Lydekker, 1893; Bonaparte,

1996)Argyrosaurus sp. (Powell, 1986; Bonaparte, 1996)Titanosaurinae indet. (Powell et al., 1989; Sciutto and

Martınez, 1994)Ornithopoda

Notohypsilophodon comodorensis (Martınez, 1998a)

The Bajo Barreal has produced a diverse terrestrial vertebratefauna (Table 1), consisting of chelonians, crocodyliforms, anddinosaurs (Martınez et al., 2000). Of the latter, theropods arerepresented by a fragmentary long-clawed genus (Martınez etal., 1999), the neoceratosaurian Xenotarsosaurus bonapartei(Martınez et al., 1986; Coria and Rodriguez, 1993), the maxilladescribed here, and a small probable coelurosaur known frompostcranial remains of several individuals (Martınez and Novas,1997). The sauropod fauna is diverse as well, and includes di-plodocoids (Sciutto and Martınez, 1994; Martınez, 1998c), anundescribed titanosauriform represented by an excellent skulland cervical vertebrae (Martınez, 1998b, 1999), the basal tita-nosaur Andesaurus sp. (Sciutto and Martınez, 1997), and thetitanosaurids Epachthosaurus scuittoi (Powell, 1990) and Argy-rosaurus (Lydekker, 1893; Powell, 1986; Bonaparte, 1996). Or-nithischian dinosaurs are represented by the ornithopod No-tohypsilophodon comodorensis (Martınez, 1997, 1998a).

DESCRIPTION

Lateral

Much of the lateral surface of UNPSJB-PV247 (Fig. 2A) isornamented with distinctive sculpturing, composed of subpar-allel, crescentic ridges and furrows recalling the maxilla of theabelisaurid Majungatholus (Sampson et al., 1998). The elementis dorsoventrally deep relative to its length compared to otherlarge theropod maxillae such as those of Allosaurus fragilis(Madsen, 1976) and Acrocanthosaurus atokensis (Currie andCarpenter, 2000) (Table 2). Again, this condition is similar tothat in other abelisaurids, especially Majungatholus (Sampsonet al., 1998) and AMNH 1955, a maxilla previously attributedto Indosuchus (Chatterjee, 1978). UNPSJB-PV247 does notpossess lateral convexities corresponding to the roots of erupted

crowns and replacement teeth, which are clearly visible in sometheropods (e.g., Buffetaut et al., 1988; Sereno et al., 1996).

The rostral ramus of the new maxilla is strongly reduced, incontrast to many non-abelisauroid theropods. In Carnotaurus,the rostral ramus is practically nonexistent (Bonaparte et al.,1990), whereas in Noasaurus and Majungatholus it is plesio-morphically more rostrocaudally elongate (Bonaparte and Pow-ell, 1979; Sampson et al., 1998). UNPSJB-PV247 exhibits anintermediate morphology (Fig. 3).

The antorbital region of the new maxilla shows several char-acters suggestive of relationship to Abelisauroidea. The rostralmargin of the ascending ramus of the maxilla is not inclinedcaudally as it is in many theropods (e.g., Allosaurus, Madsen,1976; Carcharodontosaurus, Sereno et al., 1996; Coelophysis,Colbert, 1989; Ceratosaurus, Madsen and Welles, 2000); in-stead it is nearly vertical, to a degree surpassing that of someabelisaurids (Fig. 3). A single expansive recess invades the as-cending ramus, rendering it entirely hollow. This vacuity com-municates with the antorbital fossa via a prominent fenestra thatis obscured in lateral view by the lamina lateralis of the as-cending ramus. The caudally-facing opening is elliptical inshape and narrows dorsally. The identity of this structure isproblematic; nevertheless, it appears homologous to the pro-maxillary fenestra of tetanuran theropods (Witmer, 1997). Asin Dilophosaurus wetherilli and abelisauroids (Witmer, 1997),there is no evidence of a true maxillary fenestra in UNPSJB-PV247.

A remnant of an antorbital fossa is present on the lateralsurface of the maxillary body as a shallow depression. It isclearly demarcated by an abrupt change in surface texture, fromMajungatholus-like rugose sculpturing to a smooth, even tex-ture. Caudolaterally, there is another marked change in textureassociated with the jugal articulation. As in other abelisaurids,the jugal laterally overlaps the maxilla and its contact is elon-gate.

Medial

The element’s most notable feature in medial view is a sub-horizontal row of prominent foramina, presumably for the pas-sage of the dental arteries (Fig. 2B). Only ten are well-pre-served, but there appear to have been an additional four. Theirspacing varies with their position on the specimen (Table 3).The row of dental foramina is bordered dorsally by a conspic-uous increase in thickness, a medial maxillary ‘‘shelf’’ [the to-rus maxillaris of Witmer (1997)], very similar to that presentin AMNH 1955 (Chatterjee, 1978). The shelf becomes ridgelikecaudally, beginning at mx9, and maximizing in dorsoventraldepth between mx10–mx11. The ridge tapers to a width of ap-proximately 1 mm at the caudal margin of the maxilla. Theridge demarcates a noticeable change in maxillary surface to-pography, from a series of heavily ridged and furrowed fusedinterdental plates (as in Majungatholus and AMNH 1955) to aneven texture. This fusion of the interdental plates is comparableto the condition in Allosaurus (Madsen, 1976:pl. 6) but con-trasts with that in Sinraptor dongi (Currie and Zhao, 1993:fig.4), in which the interdental plates are clearly distinct from oneanother. In the new Patagonian maxilla, the ridges and furrowson the interdental plates are subvertical at the premaxillary ar-ticulation. Caudally, their dorsal portions become inclined ros-trally.

Small depressions are present immediately dorsal to the al-veoli, and are more clearly defined rostrally. The slight ridgesbetween them probably correspond to tooth roots and replace-ment teeth inside the element. A prominent, hollow rostrome-dial process arises ventral to the ascending ramus. A depressionborders the rostromedial process ventrally, similar to the con-dition reported in AMNH 1955 (Chatterjee, 1978).


FIGURE 2. Abelisaurid maxilla, UNPSJB-PV247. A, lateral view; B, medial view; C, rostral view; D, ventral view. Abbreviations listed in text.Scale bar equals 10 cm.

TABLE 2. Measurements (mm) and length/depth ratios of the new maxilla, compared to the corresponding element in the abelisaurid Majun-gatholus (FMNH PR2100; Sampson et al., 1998) and the allosauroid Acrocanthosaurus (NCSM 14345; Currie and Carpenter, 2000). The similarityof C and D in both abelisaurids represents the nearly parallel dorsal and ventral margins of their maxillae. Note the much lower length/depthratios in the abelisaurids, indicating maxillae deeper per unit length than that of A. atokensis. * 5 element incomplete.

UNPSJB-PV247 Majungatholus atopusAcrocanthosaurus

atokensis

A. Rostrocaudal lengthB. Maximum dorsoventral depthC. Dorsoventral depth at jugal articulationD. Dorsoventral depth, alveolar margin to base of lamina medialisE. Length/depth at jugal articulation (A/C)F. Length/depth at base of lamina medialis (A/D)

330186*

94102

3.513.24

;290182

70834.143.49

82031276

13110.796.26


FIGURE 3. Theropod maxillae in lateral view. A, Allosaurus fragilis (after Madsen, 1976). B, Carcharodontosaurus saharicus (after Sereno etal., 1996). C, Coelophysis bauri (after Colbert, 1989). D, Ceratosaurus dentisulcatus (after Madsen and Welles, 2000). E, Noasaurus leali (afterBonaparte and Powell, 1980). F, Abelisaurus comahuensis (after Bonaparte and Novas, 1985). G, Carnotaurus sastrei (after Bonaparte et al.,1990). H, AMNH 1955 (after Chatterjee, 1978). I, Majungatholus atopus (after Sampson et al., 1998). J, UNPSJB-PV247. Note the caudalinclination in the maxillary ascending ramus of A. fragilis, C. saharicus, C. bauri, and C. dentisulcatus. This structure is nearly vertical inabelisauroids, most apparent in C. sastrei, AMNH 1955, and UNPSJB-PV247. Scale bar equals 10 cm in A, D, F–J; 50 cm in B; 2.5 cm in C, E.

TABLE 3. Distances between medial dental foramina (in mm),UNPSJB-PV247, measured midpoint-midpoint.

Number Distance between

1–22–33–44–55–66–77–88–99–10

10–1111–1212–1313–14

18.020.520.021.020.021.521.017.023.021.017.020.016.0

Rostral

Three prominent depressions are visible in rostral view (Fig.2C). They may indicate an undulating premaxillary–maxillarysuture. The maxilla and the premaxilla (judging from its artic-ulation) are laterally convex.

Caudal

A prominent groove for articulation with the jugal is evident.This suture gradually sweeps laterally approaching the ventralmargin of UNPSJB-PV247, indicating an increase in skullwidth.

Ventral

The 14–15 alveoli are distinguishable in ventral view (Fig.2D). The lateral alveolar margin extends farther ventrally thanthe medial, most noticeably in the region of mx4–mx9. Therow of alveoli displays a slight sigmoidal curvature. The rostralportion (encompassing mx1–mx3) of the tooth row arches gent-ly laterally, then becomes inclined roughly caudally, parallel tothe midline of the skull. In the area of mx12 the ventral marginflares more sharply, again in a lateral direction.

Dentition

Erupted or partially erupted tooth crowns are present in al-veoli 1, 3, 4, 5, 7, 8, 10, 11, 12, 13, and 14. Of these, mx12 isthe best preserved. It is labiolingually compressed and possess-es denticulate mesial and distal carinae. It is unknown whetherthe carinae are denticulate to the crown tip, although the con-


FIGURE 4. Preliminary hypothesis of phylogenetic relationships forseven neoceratosaurian taxa based on a parsimony analysis of 11 max-illary characters and using Coelophysis bauri as an outgroup. Nodedesignations follow these sources: Neoceratosauria, Novas, 1991; Abe-lisauroidea, Bonaparte, 1991b; Abelisauridae, Bonaparte and Novas,1985; and Carnotaurinae, Sereno, 1998. The biogeographic and tem-poral distribution of all taxa is given (concept after Sampson et al.,1998; De Klerk et al., 2000). The earliest known abelisaurid is the BajoBarreal form, UNPSJB-PV247, from the Late Cenomanian–Early Tu-ronian (;94 Ma).

dition in mx8 suggests this. The carinae are aligned with themesiodistal axis of the tooth, and are not offset as in the distalmaxillary crowns of some other theropods (e.g., Allosaurus,JBS., pers. obs. 1998; Acrocanthosaurus, many tyrannosaurids,Holtz, pers. comm., 1999).

Mx12 is nearly fully erupted, and occupies much of thelength of its alveolus. It measures 14 mm in crown base length[following Smith and Dodson, in press; 5FABL of severalworks (e.g., Currie et al., 1990)], approximately 11 mm incrown base width, and has an average mesial denticle densityof 12/5 mm (2.4/mm). The crown is thus low compared to thesize of the maxilla and strongly dissimilar to the tall crowns ofmany other large theropods (e.g., Ceratosaurus, Marsh, 1884;Madsen and Welles, 2000; allosauroids, Madsen, 1976; Currieand Zhao, 1993; Sereno et al., 1996; Currie and Carpenter,2000; tyrannosaurids, Osborn, 1912; Lambe, 1914, 1917).Mx12 recalls crowns of Majungatholus and AMNH 1955.Crowns of Carnotaurus are elongate and slender, dissimilarfrom those of other abelisaurids (Bonaparte, 1991b).

Comparison with Xenotarsosaurus bonapartei

UNPSJB-PV247 was recovered from the same horizon of theBajo Barreal, approximately 150 m from the type locality ofthe medium-sized theropod Xenotarsosaurus bonapartei (Mar-tınez et al., 1986). The stratigraphic and geographic proximityof the new maxilla to Xenotarsosaurus raises the possibility thatthe two entities pertain to the same taxon. However, no directanatomical comparisons can be made between them. The ho-lotype of X. bonapartei includes a femur, fibula, tibia, astraga-localcaneum, and two incomplete cranial dorsal vertebrae. Theelements of Xenotarsosaurus exhibit neoceratosaurian charac-ters, but as nearly all recognized abelisaurid synapomorphiespertain to cranial or cervical morphology, the taxon has beenexcluded from Abelisauridae in recent works (Coria and Ro-drıguez, 1993; Coria and Salgado, 1998; Sampson et al., 1998).

The dimensions of the involved elements may provide evi-dence against the referral of UNPSJB-PV247 to Xenotarsosau-rus. UNPSJB-PV247 measures 330 mm in rostrocaudal length,some 13.8% longer than the maxilla of the Malagasy abelisau-rid Majungatholus (Table 2). The total body length of Majun-gatholus has been estimated at 7 to 9 m (Sampson et al., 1998).If it was of similar proportions, the Bajo Barreal theropod rep-resented by the maxilla reached 8 to 10 m in length. The fem-oral length of Xenotarsosaurus is 598 mm, indicating an animalroughly 5 m in total length (based on comparison with Car-notaurus sastrei, Bonaparte et al., 1990). In addition, the dorsalneural arches of X. bonapartei are fused to their respective cen-tra, possibly indicating that this animal had neared adult bodysize at the time of its death (Brochu, 1996). It is possible thatthe new maxilla, which may indicate an animal 8 m or morein length, does not pertain to Xenotarsosaurus. Two or moreneoceratosaurian genera may be present in the Bajo Barrealfauna, as is the case in the Maastrichtian Lameta assemblageof India (Huene and Matley, 1933; Chatterjee, 1978; Sampsonet al., 1998; Novas and Bandyopadhyay, 1999).

PHYLOGENETIC ANALYSIS

A preliminary phylogenetic analysis of neoceratosaurian taxawas conducted to assess the evolutionary relationships and bio-geographic significance of the Bajo Barreal theropod. The seveningroup taxa included Abelisaurus (MC 11098), AMNH 1955,Carnotaurus (MACN-CH 894), Ceratosaurus (USNM 4735;MWC 1; UMNH 5278), Majungatholus (FMNH PR2100), Noa-saurus leali (PVL 4061), and UNPSJB-PV247. Nine binary andtwo multistate maxillary anatomical characters were coded foreach taxon (Appendix 1). Multistate characters were consideredunordered, and polarity was determined using the coelophysoid

theropod Coelophysis bauri (Colbert, 1989) as an outgroup.Character states in each terminal taxon were determined usinginformation from the literature, personal communication, or di-rect observation (Appendix 2).

The analysis was conducted using PAUP* [(PhylogeneticAnalysis Using Parsimony (*and Other Methods)], Version4.0b4a (Swofford, 2000) with the ‘collapse’ option in effect.The small size of the matrix permitted use of the exhaustivesearch method. Due to missing anatomical information for sev-eral ingroup taxa, namely Abelisaurus, AMNH 1955, Noasau-rus, and UNPSJB-PV247, preliminary attempts to incorporatenon-maxillary cranial, axial, and appendicular morphology re-sulted in many most parsimonious trees, the consensus of whichwas invariably a phylogenetically uninformative polytomy.

RESULTS

The phylogenetic analysis produced a single most parsimo-nious tree of 16 steps (Fig. 4), demonstrating the abelisauridaffinities of UNPSJB-PV247. The tree has high consistency,retention, and rescaled consistency indices (0.81, 0.80, 0.65),due largely to the small size of the character matrix. The treesupports a monophyletic Abelisauridae, and within it, a Car-notaurinae composed of Carnotaurus, AMNH 1955, Majun-gatholus, and the Bajo Barreal form. Bremer support indices(Bremer, 1988) for each node determined using TreeRot, Ver-sion 2 (Sorenson, 1999) are as follows: Abelisauroidea 1.0;Abelisauridae 2.0; Carnotaurinae 1.0; and unnamed clade(AMNH 1955-Majungatholus-UNPSJB-PV247) 1.0.


DISCUSSION

Relationships of Ingroup Taxa

Neoceratosauria: Ceratosaurus Ceratosaurus is a largetheropod from the Upper Jurassic of western North Americawhose phylogenetic relationships have become controversial inrecent years. The systematic work of Rowe and Gauthier (1990)allied the genus to coelophysoid theropods in a monophyleticassemblage termed Ceratosauria. Within this clade, Ceratosau-rus is usually regarded as the sister-taxon to Abelisauria; to-gether they constitute Neoceratosauria (Novas, 1991; Holtz,1994, 1998; Coria and Salgado, 1998).

Several preliminary analyses have raised evidence against themonophyly of Ceratosauria (Currie, 1995; Britt, 1995; Rauhut,1998; Carrano and Sampson, 1999; Forster, 1999). In the cur-rent study, Ceratosaurus united with Abelisauroidea in a mono-phyletic Neoceratosauria. However, theropod genera tradition-ally regarded as tetanuran were not included in the present anal-ysis, precluding scrutiny of the monophyly of Ceratosauria. Ce-ratosaurus is provisionally accepted as the sister-taxon toAbelisauria, pending several works in progress (Coria and Cur-rie, 1997; Rauhut, 1998; Carrano and Sampson, 1999).

Abelisauroidea: Noasaurus leali Noasaurus, from the?Maastrichtian Lecho Formation of Argentina is generally re-garded as an abelisaur, but outside of Abelisauridae and placedin Noasauridae (Bonaparte and Powell, 1980; Bonaparte,1991b; Novas, 1997b, c; Coria and Salgado, 1998). The maxillaof this animal shares several derived characters with those ofabelisaurids, such as a reduced rostral ramus and a subverticalascending ramus. Nonetheless, it retains a very well-developedantorbital fossa on the maxillary body, and lacks several post-cranial apomorphies of Carnotaurus (Bonaparte, 1991b). Noa-saurus is regarded as a member of the sister-taxon to Abelisau-ridae.

Abelisauridae The monophyly of Abelisauridae is sup-ported by the analysis. Maxillary synapomorphies linking abe-lisaurids include external maxillary sculpture (apparently re-versed in AMNH 1955) and a strong reduction in size of theantorbital fossa on the main body of the maxilla.

Abelisaurus comahuensis Abelisaurus is a large Late Cre-taceous Argentine theropod with hypothesized close affinity toCarnotaurus and its relatives (Bonaparte et al., 1990; Bonapar-te, 1991b). However, Abelisaurus lacks or is indeterminate forsynapomorphies of Carnotaurinae, and thus cannot be referredto that clade (Sereno, 1999). Furthermore, several maxillarycharacters that it shares with carnotaurines are also found inthe allosauroid carcharodontosaurids (Rauhut, 1995; Sereno etal., 1996) Giganotosaurus carolinii and Carcharodontosaurussaharicus (Novas, 1997b; Sampson et al., 1998).

A number of authors have commented upon remarkable sim-ilarities in cranial morphology between the abelisaurid and car-charodontosaurid clades (Coria and Salgado, 1995; Novas,1997b; Holtz, 1998; Sampson et al., 1998; Forster, 1999). Sim-ilar features include reduced antorbital fossae, rugose nasals andmaxillae, a lacrimal and postorbital union forming eave-likebrows, and invasion of the orbital fenestrae by the lacrimal andpostorbital (Coria and Salgado, 1995; Novas, 1997b). The re-semblances have been explained either as the result of conver-gence (Coria and Salgado, 1995; Holtz, 1998; Sampson et al.,1998) or as evidence for close phylogenetic affinity betweenthe two groups (Novas, 1997b, c). Due to the reported dissim-ilarity in postcranial morphology between Carnotaurus and Gi-ganotosaurus (Coria and Salgado, 1995), it seems appropriateto invoke homoplasy as an explanation for these putative cranialsynapomorphies. However, as Abelisaurus is at present knownonly from cranial remains and cannot be verified for any car-notaurine syapomorphies, it is possible that it pertains to Car-charodontosauridae. Its resemblance to Giganotosaurus is par-

ticularly striking. In addition to the possible synapomorphiesdetailed above, Abelisaurus and Gigantosaurus share stronglycaudoventrally inclined quadrates resulting in a mandibular ar-ticulation far caudal to the occiput (Bonaparte and Novas, 1985;Coria and Salgado, 1995; Currie and Carpenter, 2000). As asimilar situation is present in Ceratosaurus, however, this char-acter may be plesiomorphic (Marsh, 1884; Gilmore, 1920).Postcranial material of Abelisaurus is needed to more adequate-ly establish its affinities and biogeographic implications.

Carnotaurinae The morphological characters assembled inthis study support a subclade within Abelisauridae composedof Majungatholus, Carnotaurus, Indosuchus, and the Bajo Bar-real abelisaurid termed Carnotaurinae (Sereno, 1998). The BajoBarreal form extends the temporal range of carnotaurines froman exclusively Senonian to a late Cenomanian–Maastrichtianoccurrence (Fig. 4).

Maxillary synapomorphies linking carnotaurines include apromaxillary fenestra obscured in lateral view by the laminalateralis of the ascending ramus, a maxillary body with sub-parallel dorsal and ventral margins, and possibly rostrocaudallyshortened maxillae and an elongate maxilla-jugal contact. Theformer also occurs in several tetanuran theropods, particularlyAllosaurus, Proceratosaurus, and some tyrannosaurids (Witmer,1997; Holtz, 1998).

Carnotaurus sastrei The osteology of Carnotaurus, recov-ered from northern Chubut Province and well known for itsconspicuous frontal ‘‘horns,’’ has been of tremendous impor-tance to abelisaurid systematics (Bonaparte et al., 1990). Theholotype of C. sastrei, formerly believed to be from the Albian-Cenomanian Gorro Frigio Formation, now appears to havecome from the lower portion of the Campanian–MaastrichtianLa Colonia Formation (Ardolino and Delpino, 1987; Sampsonet al., 1998; Albino, 2000; Pascual et al., 2000).

Indian Abelisaurids Over several decades, the Maastrich-tian Lameta Formation of India has yielded significant theropodspecimens, including Indosaurus matleyi and Indosuchus rap-torius as well as many isolated elements (Huene and Matley,1933). Type specimens for these taxa were selected from re-mains described in the original publication on each (GSI K27/565 and K27/685, respectively; Chatterjee, 1978). Both speciesare based upon incomplete braincase material. Indosaurus hastraditionally been regarded as an Allosaurus-like taxon, a ‘meg-alosaur’ (Huene and Matley, 1933; Walker, 1964; Chatterjee,1978). Recent works have strived for more precise identifica-tion, and modern workers generally treat this form as an abe-lisaurid (Bonaparte and Novas, 1985; Molnar, 1990; Sampsonet al., 1998; Novas and Bandyopadhyay, 1999). The abelisauridaffinities of this species are suggested by its apparent possessionof cranial hornlike structures seen in some members of thisclade.

While Indosaurus has been largely overlooked in the litera-ture, Indosuchus has received more attention. Like the former,Indosuchus was originally regarded as an allosaurid (Huene andMatley, 1933); however, Walker (1964), referred this genus toTyrannosauridae, noting a tyrannosaurid-like median crest be-tween the supratemporal fenestrae in the specimen that was tobe the lectotype. This assignment was followed by Chatterjee(1978), who, largely based on the alleged tyrannosaurid statusof Indosuchus, referred to it several isolated cranial elements,including a maxilla included in the present analysis, AMNH1955.

In more recent years, comparisons of the lectotype with Abe-lisaurus and Carnotaurus have led to the current view of In-dosuchus as an abelisaurid (Bonaparte et al., 1990; Molnar,1990; Chatterjee and Rudra, 1996; Novas and Bandyopadhyay,1999). Additional material from the Lameta Formation has beenreferred to this taxon, including cranial remains and a disartic-ulated postcranial skeleton (Chatterjee, 1978; Chatterjee and


Rudra, 1996). Still, none of the elements attributed to Indosu-chus have been associated with braincase material necessary toconfirm their referral. Furthermore, it is likely that some spec-imens referred to Indosuchus pertain to other genera, as at leastone other probable abelisaurid (Indosaurus) and a small prob-able abelisaur (Laevisuchus) have been recognized from the La-meta (Sampson et al., 1998; Novas and Bandyopadhyay, 1999).We reserve the name Indosuchus for the lectotype (GSI K27/685), and view all referred material (including AMNH 1955)as Abelisauridae, gen. et sp. indet. pending further discoveries.

Majungatholus atopus Outstanding new specimens fromthe Maastrichtian Maevarano Formation of Madagascar haverevealed the abelisaurid affinities of Majungatholus (Sampsonet al., 1996; 1998; O’Connor and Sampson, 1998), originallydescribed as a Gondwanan pachycephalosaur (Sues and Taquet,1979; Sues, 1980). Sampson et al. (1998) postulated prolongedbiotic and physical connections between selected landmasses ofthe former Gondwanan supercontinent, based in part upon abe-lisaurid biogeography. In light of the recognition of the BajoBarreal predator as an abelisaurid closely related to Majungat-holus, Carnotaurus, and AMNH 1955, these hypotheses are re-evaluated below.

Biogeographic Implications

According to current paleogeographic reconstructions, theCretaceous witnessed the disassembly of the southern super-continent of Gondwana. However, many issues concerning thetiming and sequence of this process remain unresolved. Themajority of proposed Cretaceous paleogeographic scenarios(e.g., Scotese and Golonka, 1993; Smith et al., 1995; Roeser etal., 1996; Scotese, 1997) detail a rapid dissociation of Gond-wanan landmasses, with India-Madagascar separating com-pletely from the Antarctica–Australia complex by the upperBarremian (Early Cretaceous, ca. 125 Ma; Gradstein et al.,1995, 1997). According to these hypotheses, South Americasevered physical ties with Africa during the Aptian or Albian(prior to 100 Ma), but portions of these landmasses remainedin fairly close proximity throughout much of the Cretaceous(Scotese and Golonka, 1993). India and Madagascar wereamong the last southern landmasses to dissociate, separating atca. 88.0 Ma (Storey et al., 1995). The isolation of South Amer-ica was finally completed in the Tertiary, when it broke fromAntarctica.

According to the recent hypothesis of Hay et al. (1999), adifferent scenario is likely: India-Madagascar and South Amer-ica remained united via Sri Lanka, the Kerguelen Plateau, andAntarctica well into the Senonian, subsequent to the divergenceof South America and Africa. Africa became an ‘‘island con-tinent’’ for the entirety of the Late Cretaceous.

Biogeographic study has potential to help resolve tectonichypotheses. Continental dispersal of terrestrial vertebrates ap-pears strongly controlled by the presence or absence of seas.Landlocked faunas developing on Gondwanan continents geo-graphically isolated from one another should show increasingdegrees of endemism over time. If the former, more conven-tional geophysical model reflects the actual sequence of eventsin Gondwanan breakup, then the Cenomanian–Turonian terres-trial vertebrate fauna of South America should resemble that ofAfrica more closely than those of India and Madagascar. Ap-tian–Albian faunal exchange between Africa and South Amer-ica would have likely resulted in early Late Cretaceous cladesnative to both, but absent from an isolated India–Madagascar.Conversely, if the Hay et al. proposal proves correct, then thevertebrates of South America should be more phylogeneticallyallied to those of India and Madagascar than Africa. Late Cre-taceous Africa should have hosted an isolated, endemic verte-brate fauna.

Despite many recent finds, the Cretaceous record of terres-trial vertebrates, including dinosaurs, in Gondwanan landmass-es remains incomplete. In all Southern Hemisphere continents,even comparatively well-documented South America, there iscurrently no information on dinosaurian assemblages for entireCretaceous temporal ages. Particularly frustrating is the lack ofspecimens from time intervals pertinent to the resolution of thepaleogeographic controversy described above. Examples in-clude the lack of Senonian dinosaur remains from Africa andthe paucity of pre-Campanian Cretaceous terrestrial vertebratesfrom India or Madagascar.

Nevertheless, researchers have recently cited the geographicoccurrence of abelisaurids as evidence in support of a Late Cre-taceous dispersal route between India-Madagascar, Antarctica–Australia, and South America (Sampson et al., 1998). Theseauthors consider the origins of Abelisauridae to have postdatedrifting between South America and Africa, but to have predatedthe separation of India and Madagascar in the Coniacian. Ac-cording to their hypothesis, abelisaurids never existed in Africa.Strictly speaking, the Bajo Barreal maxilla and the neocerato-saurian phylogeny recovered in this analysis are in accordancewith this hypothesis, and with the tectonic model of Hay et al.(1999), as abelisaurids remain limited to Upper Cretaceous de-posits of South America, India, and Madagascar.

Still, the Cenomanian–Turonian occurrence of the Bajo Bar-real form raises some questions concerning the timing of abe-lisaurid origins, the biogeography of the clade, and its utility inpaleogeographic reconstruction. Prior to the recognition ofUNPSJB-PV247 as an abelisaurid, the group was believed tobe temporally limited to Campanian-Maastrichtian deposits(Sampson et al., 1998). The recovery of the new maxilla inCenomanian–Turonian strata represents a substantial range ex-tension for the clade. Estimates of the time interval duringwhich abelisaurids originated depend on the use of delayed oraccelerated transformations. If delayed divergence estimates areused, Abelisauridae originated immediately prior to the Ceno-manian-Turonian. However, if accelerated estimates are em-ployed, the clade may have originated many millions of yearsprior to the Late Cretaceous. It is likely that the rise of Abeli-sauridae predated the separation of Africa and South America,and thus, that abelisaurids could have occupied Africa duringat least some Cretaceous intervals. Moreover, the known oc-currence of Abelisauridae may reflect a former pan-Gondwanandistribution, and is thus of limited utility in the support of LateCretaceous paleogeographic hypotheses until phylogenetic af-finities within the clade are resolved.

ACKNOWLEDGMENTS

We thank M. Luna and G. Casal for aid in recovery, prepa-ration, and casting of UNPSJB-PV247. We are indebted to J. F.Bonaparte, J. S. Bridge, E. Buffetaut, M. T. Carrano, S. Chat-terjee, R. A. Coria, C. A. Forster, W. W. Hay, T. R. Holtz, Jr.,E. A. Musacchio, D. A. Russell, S. D. Sampson, P. Vallati-Sandoval, and L. M. Witmer for valuable discussion and accessto unpublished information. M. Luna provided a Spanish trans-lation of the English abstract. Early drafts of the manuscriptbenefited greatly from reviews by P. Dodson, J. D. Harris, andC. E. Vaughn. M. T. Carrano, C. A. Forster, T. R. Holtz, Jr, andF. E. Novas provided valuable reviews of the final manuscript.This research was supported by the University of Pennsylvania(Paleobiology Stipends to Lamanna and Smith), the Universi-dad Nacional de la Patagonia ‘‘San Juan Bosco,’’ the NationalGeographic Society Committee for Research and Exploration(Grant #6646-99), the Jurassic Foundation, and the DelawareValley Paleontological Society.


LITERATURE CITED

Albino, A. M. 2000. New record of snakes from the Cretaceous ofPatagonia (Argentina). Geodiversitas 22:247–253.

Archangelsky, S., E. S. Bellosi, G. A. Jalfin, and C. Perrot. 1994. Pal-ynology and alluvial facies from the mid-Cretaceous of Patagonia,subsurface of San Jorge Basin, Argentina. Cretaceous Research 15:127–142.

Ardolino, A., and D. Delpino. 1987. Senoniano (continental-marino),Comarca Nordpatagonica, Provincia del Chubut, Argentina. Deci-mo Congreso Geologico Argentino, San Miguel de Tucuman, ActasIII:193–196.

Astibia, H., E. Buffetaut, A. D. Buscalioni, H. Cappetta, C. Corral, R.Estes, F. Garcia-Garmilla, J. J. Jaeger, E. Jimenez-Fuentes, J. LeLoueff, J. M. Mazin, X. Orue-Extebarria, J. Pereda-Suberbiola, J.E. Powell, J. C. Rage, J. Rodriguez-Lazaro, J. L. Sanz, and H.Tong. The fossil vertebrates from Lano (Basque Country, Spain);new evidence on the composition and affinities of Late Cretaceouscontinental faunas of Europe. Terra Nova 2:460–466.

Bonaparte, J. F. 1985. A horned Cretaceous carnosaur from Patagonia.National Geographic Research 1:149–151.

——— 1986. History of the terrestrial Cretaceous vertebrates of Gond-wana. Congreso Argentino Paleontologia y Bioestratgrafia 4, Actas2:63–95.

——— 1991a. Los vertebrados fosiles de la Fm. Rıo Colorado, de laciudad de Neuquen y cercanıas, Cretacico Superior, Argentina. Re-vista Museo Argentino de Ciencias Naturales ‘‘Bernardino Riva-davia’’ 4(3):17–123.

——— 1991b. The Gondwanian theropod families Abelisauridae andNoasauridae. Historical Biology 5:1–25.

——— 1996. Cretaceous tetrapods of Argentina. Munchner Geowis-senschafte Abhandlungen (A) 30:73–130.

———, and Z. B. de Gasparini. 1979. Los sauropodos de los gruposNeuquen y Chubut y sus relaciones cronologicas. Actas VII Con-greso Geologico Argentino Neuquen 2:393–406.

———, and F. E. Novas. 1985. Abelisaurus comahuensis n. g., n. sp.,Carnosauria del Cretacico tardio de Patagonia. Ameghiniana 21:259–265.

———, ———, and R. A. Coria. 1990. Carnotaurus sastrei Bonaparte,the horned, lightly built carnosaur from the Middle Cretaceous ofPatagonia. Natural History Museum of Los Angeles County Con-tributions in Science 416:1–42.

———, and J. E. Powell. 1980. A continental assemblage of tetrapodsfrom the Upper Cretaceous beds of El Brete, northwestern Argen-tina. Memoires de la Societe Geologique de France, N. Ser. 139:19–28.

Bremer, K. 1988. The limits of amino acid sequence data in angiospermphylogenetic reoconstruction. Evolution 42:795–803.

Bridge, J. S., G. A. Jalfin, and S. M. Georgieff. 2000. Geometry, lithofa-cies, and spatial distribution of Cretaceous fluvial sandstone bodies,San Jorge Basin, Argentina: outcrop analog for the hydrocarbon-bearing Chubut Group. Journal of Sedimentary Research 70:341–359.

Britt, B. 1995. The nature and distribution of pneumatic vertebrae inthe Theropoda. Journal of Vertebrate Paleontology 15(3, suppl.):20A.

Brochu, C. A. 1996. Closure of neurocentral sutures during crocodilianontogeny: implications for maturity assessment in fossil archosaurs.Journal of Vertebrate Paleontology 16:49–62.

Broin, F. de, and M. de la Fuente. 1993. Les tortues fossiles d’Argentine:synthese. Annales de Paleontologie 79:169–232.

Buffetaut, E. 1989. Archosaurian reptiles with Gondwanan affinities inthe Upper Cretaceous of Europe. Terra Nova 1:69–74.

———, P. Mechin, and A. Mechin-Salessy. 1988. Un dinosaure the-ropode d’affinites gondwaniennes dans le Cretace superieur de Pro-vence. Comptes Rendus de l’Academie des Sciences de Paris 306:153–158.

Carrano, M. T., and S. D. Sampson. 1999. Evidence for a paraphyletic‘Ceratosauria’ and its implication for theropod dinosaur evolution.Journal of Vertebrate Paleontology 19(3, suppl.):36A.

Chatterjee, S. 1978. Indosuchus and Indosaurus, Cretaceous carnosaursfrom India. Journal of Paleontology 52:570–580.

———, and D. K. Rudra. 1996. KT events in India: impact, rifting,volcanism, and dinosaur extinction. Memoirs of the QueenslandMuseum 39:489–532.

Colbert, E. H. 1989. The Triassic dinosaur Coelophysis. Museum ofNorthern Arizona, Bulletin 57:1–160.

Coria, R. A., L. M. Chiappe, and L. Dingus. 2000. A new abelisaurtheropod from the Upper Cretaceous of Patagonia. Journal of Ver-tebrate Paleontology 20(3, suppl.):36–37A.

———, and P. J. Currie. 1997. A new theropod from the Rio LimayFormation. Journal of Vertebrate Paleontology 17(3, suppl.):40A.

———, and J. Rodriguez. 1993. Sobre Xenotarsosaurus bonaparteiMartınez, Gimenez, Rodriguez, y Bochatey, 1986; un problematicoNeoceratosauria (Novas, 1989) del Cretacico de Chubut. Ameghi-niana 30:326–327.

———, and L. Salgado. 1995. A new giant carnivorous dinosaur fromthe Cretaceous of Patagonia. Nature 377:224–226.

———, and ——— 1998. A basal Abelisauria Novas 1992 (Thero-poda-Ceratosauria) from the Cretaceous of Patagonia, Argentina,pp. 89–101 in B. Perez-Moreno, T. R. Holtz, Jr., J. L. Sanz, and J.Moratalla (eds.), Aspects of Theropod Paleobiology. Gaia 15:89–102.

Currie, P. J. 1995. Phylogeny and systematics of theropods (Dinosauria).Journal of Vertebrate Paleontology 15(3, suppl.):25A.

———, and K. Carpenter. 2000. A new specimen of Acrocanthosaurusatokensis (Theropoda, Dinosauria) from the Lower Cretaceous Ant-lers Formation (Lower Cretaceous, Aptian) of Oklahoma, USA.Geodiversitas 22:207–246.

———, J. K. Rigby, Jr., and R. E. Sloan. 1990. Theropod teeth fromthe Judith River Formation of southern Alberta, Canada; pp. 107–125 in P. J. Currie and K. Carpenter (eds.), Dinosaur Systematics:Approaches and Perspectives. Cambridge University Press, NewYork.

———, and X.-J. Zhao. 1993. A new carnosaur (Dinosauria: Thero-poda) from the Jurassic of Xinjiang, People’s Republic of China.Canadian Journal of Earth Sciences 30:2231–2247.

De Klerk, W. J., C. A. Forster, S. D. Sampson, A. Chinsamy, and C. F.Ross. 2000. A new coelurosaurian dinosaur from the Early Creta-ceous of South Africa. Journal of Vertebrate Paleontology 20:324–332.

Forster, C. A. 1999. Gondwanan dinosaur evolution and biogeographicanalysis. Journal of African Earth Sciences 28:169–185.

Gilmore, C. W. 1920. Osteology of the carnivorous Dinosauria in theUnited States National Museum, with special reference to the gen-era Antrodemus (Allosaurus) and Ceratosaurus. United States Na-tional Museum Bulletin 110:1–154.

Gradstein, F. M., F. P. Agterberg, J. G. Ogg, J. Hardenbol, P. van Veen,J. Thierry, and Z. Huang. 1995. A Triassic, Jurassic, and Cretaceoustimescale; pp. 95–126 in W. A. Berggren, D. V. Kent, M. P. Aubry,and J. Hardenbol (eds.), Geochronology Time Scales and GlobalStratigraphic Correlation. Society of Sedimentary Geology SpecialPublication 54.

———, J. Ogg, F. P. Agterberg, J. Hardenbol, and P. van Veen. 1997.Some contstraints on the Phanerozoic timescale; pp. 11–19 in WangN. and J. Remane (eds.), Proceedings of the 30th International Geo-logical Congress. Beijing, China.

Hay, W. W., R. DeConto, C. N. Wold, K. M. Wilson, S. Voigt, M.Schulz, A. Wold-Rossby, W. C. Dullo, A. B. Ronov, A. N. Baluk-hovsky, and E. Soding. 1999. An alternative global Cretaceous pa-leogeography; pp. 1–47 in E. Barrera and C. Johnson (eds.), Evo-lution of the Cretaceous Ocean/Climate System. Geological Societyof America Special Paper 332.

Holtz, T. R., Jr. 1994. The phylogenetic position of the Tyrannosauridae:implications for theropod systematics. Journal of Paleontology 68:1100–1117.

——— 1998. A new phylogeny of the carnivorous dinosaurs; pp. 5–61 in B. Perez-Moreno, T. R. Holtz, Jr., J. L. Sanz, and J. Moratalla(eds.), Aspects of Theropod Paleobiology. Gaia 15:5–61.

Huene, F. von. 1929. Los Saurisquios y Ornithisquios del Cretaceo Ar-gentino. Anales del Museo La Plata (Ser. 2) 3:1–196.

———, and C. A. Matley. 1933. The Cretaceous Saurischia and Or-nithischia of the central provinces of India. Palaeontologia Indica21:1–74.

Lamanna, M. C., J. B. Smith, K. J. Lacovara, P. Dodson, and Y. Attia.2000. New vertebrate discoveries from the Cretaceous of Egypt.Journal of Vertebrate Paleontology 20(3, suppl.):53A.

Lambe, L. M. 1914. On a new genus and species of carnivorous di-nosaur from the Belly River Formation of Alberta, with a descrip-


tion of the skull of Stephanosaurus marginatus from the same ho-rizon. The Ottawa Naturalist 28:158–164.

——— 1917. The Cretaceous theropodous dinosaur Gorgosaurus. Ca-nada Department of Mines, Geological Survey Memoir 100:1–84.

Le Loeuff, J., and E. Buffetaut. 1991. Tarascosaurus salluvicus nov.gen., nov. sp., dinosaure theropode du Cretace Superieur du sud dela France. Geobios 25:585–594.

Lydekker, R. 1893. Contributions to the study of the fossil vertebratesof Argentina. I. The dinosaurs of Patagonia. Anales del Museo deLa Plata 2:1–14.

Madsen, J. H., Jr. 1976. Allosaurus fragilis: a revised osteology. UtahGeological Survey Bulletin 109:1–163.

———, and S. P. Welles. 2000. Ceratosaurus (Dinosauria, Theropoda)a revised osteology. Utah Geological Survey Miscellaneous Pub-lication 00-2:1–80.

Marsh, O. C. 1881. Classification of the Dinosauria. American Journalof Science (Series 3) 23:81–86.

——— 1884. Principal characters of the American Jurassic dinosaurs.Pt. VIII. The Order Theropoda. American Journal of Science (Se-ries 3) 27:329–340.

Martınez, R. D. 1997. Notohypsilophodon comodorensis, un Hypsilop-hodontidae (Ornithischia: Ornithopoda) del Cretacico Superior deChubut, Patagonia central, Argentina. In Bertini, R. J. (coordena-dor), 15th Congresso Brasiliero de Paleontologia, Boletin de Re-sumos, Universidade Estadual Paulista, 92 pp.

——— 1998a. Notohypsilophodon comodorensis, gen. et sp. nov., unHypsilophodontidae (Ornithischia: Ornithopoda) del Cretacico Su-perior de Chubut, Patagonia Central, Argentina. Acta GeologicaLeopoldensia 21(46/47):119–135.

——— 1998b. An articulated skull and neck of Sauropoda from theUpper Cretaceous of central Patagonia, Argentina. Journal of Ver-tebrate Paleontology 18(3, suppl.):61A.

——— 1998c. Occurrence of dinosaur lineages with Pangean distri-bution in the Upper Cretaceous of Chubut, Central Patagonia. Bo-letin del Asociacion Paleontologica del Golfo San Jorge 2:20–21.

——— 1999. Un craneo y cuello articulado de Sauropoda (Dinosauria:Saurischia) del Cretacico Superior de Chubut. Ameghiniana 36:105.

———, O. Gimenez, J. Rodrıguez, and G. Bochatey. 1986. Xenotar-sosaurus bonapartei nov. gen. et sp. (Carnosauria, Abelisauridae),un nuevo Theropoda de la Formacion Bajo Barreal, Chubut, Ar-gentina. Actas IV: Congresso Argentina de Paleontologia y Bioes-tratigrafia 2:23–31.

———, M. C. Lamanna, J. B. Smith, G. Casal, and M. Luna. 1999.New Cretaceous theropod material from Patagonia. Journal of Ver-tebrate Paleontology 19(3, suppl.):62A.

———, ———, ———, P. Dodson, and M. Luna. 2000. Dinosaursfrom the Bajo Barreal Formation, central Patagonia. Journal of Ver-tebrate Paleontology 20(3, suppl.):57A.

———, A. Maure, M. Oliva, and M. Luna. 1993. Un maxilar de The-ropoda (Abelisauria) de la Formacion Bajo Barreal, Cretacico Tar-dio, Chubut, Argentina. Ameghiniana 30:109–110.

———, and F. E. Novas. 1997. Un nuevo tetanuro (Dinosauria: The-ropoda) de la Fm. Bajo Barreal (Cretacico Superior) Patagonia.Ameghiniana 34(4):538.

Molnar, R. E. 1990. Problematic Theropoda: ‘‘carnosaurs’’; pp. 306–317 in D. B. Weishampel, P. Dodson, and H. Osmolska (eds.), TheDinosauria. University of California Press, Berkeley.

Novas, F. E. 1991. Relaciones filogeneticas de los dinosaurios teropodosceratosaurios. Ameghiniana 28(3–4):410.

——— 1992. La evolucion de los dinosaurios carnıvoros; pp. 123–163in J. L. Sanz and A. Buscalioni (eds.), Los dinosaurios y su entornobiotico. Actas II Curso de Paleontologia en Cuenca. Instituto ‘‘Juande Valdes,’’ Ayuntamiento de Cuenca.

——— 1997a. Anatomy of Patagonykus puertai (Theropoda, Avialae,Alvarezsauridae), from the Late Cretaceous of Patagonia. Journalof Vertebrate Paleontology 17:137–166.

——— 1997b. Abelisauridae; pp. 1–2 in P. J. Currie and K. Padian(eds.), Encyclopedia of Dinosaurs. Academic Press, San Diego.

——— 1997c. South American dinosaurs; pp. 678–689 in P. J. Currieand K. Padian (eds.), Encyclopedia of Dinosaurs. Academic Press,San Diego.

——— 1998. Megaraptor namunhuaiquii, gen. et sp. nov., a large-clawed, Late Cretaceous theropod from Patagonia. Journal of Ver-tebrate Paleontology 18:4–9.

———, and S. Bandyopadhyay. 1999. New approaches on the Creta-ceous theropods from India. VII International Symposium on Me-sozoic Terrestrial Ecosystems, Abstracts.

———, and P. F. Puerta. 1997. New evidence concerning avian originsfrom the Late Cretaceous of Patagonia. Nature 387:390–392.

O’Connor, P. M., and S. D. Sampson. 1998. The vertebral column ofMajungatholus atopus (Theropoda: Abelisauridae) from the LateCretaceous of Madagascar. Journal of Vertebrate Paleontology18(3, suppl.):67A.

Osborn, H. F. 1912. Crania of Tyrannosaurus and Allosaurus. Memoirsof the American Museum of Natural History 1:1–30.

Padian, K., J. R. Hutchinson, and T. R. Holtz, Jr. 1999. Phylogeneticdefinitions and nomenclature of the major taxonomic categories ofthe carnivorous Dinosauria (Theropoda). Journal of Vertebrate Pa-leontology 19:69–80.

Pascual, R., F. J. Goin, P. Gonzalez, A. Ardolino, and P. Puerta. 2000.A highly derived docodont from the Patagonian Late Cretaceous:evolutionary implications for Gondwanan mammals. Geodiversitas22:395–414.

Powell, J. E. 1986. Revisıon de los titanosauridos de America del Sur.Ph.D. dissertation, Universidad Nacional de Tucuman, 493 pp.

——— 1990. Epachthosaurus sciuttoi, gen. et sp. nov., un nuevo di-nosaurio sauropodo del Cretacico de Patagonia (Provincia del Chu-but, Argentina). Actas V Congreso Argentino de Paleontologia yBioestratigrafia 1:123–128.

———, O. Gimenez, R. Martınez, and J. Rodriguez. 1989. Nuevo ha-llazgo de sauropodos en la Formacion Bajo Barreal de Ocho Her-manos, Sierra de San Bernardo, provincia del Chubut, y su signi-ficado cronologico. Actas, XI Congreso Brasileno de Paleontologia:165–176.

Rauhut, O. W. M. 1995. Zur systematischen Stellung der AfrikanischenTheropoden Carcharodontosaurus Stromer 1931 und Bahariasau-rus Stromer 1934. Berliner Geowissenschaftliche Abhandlungen16:357–375.

——— 1998. Elaphrosaurus bambergi and the early evolution of the-ropod dinosaurs. Journal of Vertebrate Paleontology 18(3, suppl.):71A.

Roeser, H. A., J. Fritsch, and K. Hinz. 1996. The development of thecrust off Dronning Maud Land, East Antarctica; pp. 243–264 in B.C. Storey, E. C. King, and R. A. Livermore (eds.), Weddell SeaTectonics and Gondwana Break-up. Geological Society SpecialPublication Number 108, London.

Rowe, T. R., and J. Gauthier. 1990. Ceratosauria; pp. 151–168 in D. B.Weishampel, P. Dodson, and H. Osmolska (eds.), The Dinosauria.University of California Press, Berkeley.

Russell, D. A. 1996. Isolated dinosaur bones from the Tafilalt, Morocco.Bulletin du Museum national d’Histoire naturelle 18(2–3):349–402.

Sampson, S. D., M. T. Carrano, and C. A. Forster. 2000. A theropoddinosaur with bizarre dentition from the Late Cretaceous of Mad-agascar. Journal of Vertebrate Paleontology 20(3, suppl.):66A.

———, D. W. Krause, P. Dodson, and C. A. Forster. 1996. The pre-maxilla of Majungasaurus (Dinosauria: Theropoda) with implica-tions for Gondwanan paleobiogeography. Journal of Vertebrate Pa-leontology 16:601–605.

———, L. M. Witmer, C. A. Forster, D. W. Krause, P. M. O’Connor,P. Dodson, and F. Ravoavy. 1998. Predatory dinosaur remains fromMadagascar: implications for the Cretaceous biogeography ofGondwana. Science 280:1048–1051.

Sciutto, J. C., and R. D. Martınez. 1994. Un nuevo yacimiento fosiliferode la Formacion Bajo Barreal (Cretacico Tardio) y su fauna desauropodos. Naturalia Patagonica, Ciencias de la Tierra 2:27–47.

———, and ———. 1997. El Grupo Chubut en el Anticlinal SierraNevada, Chubut, Argentina. XIII Congreso Geologico Argentina yIII Congreso de Exploracıon de Hidrocarburos, Actas I:67–75.

Scotese, C. R. 1997. Paleogeographic Atlas. PALEOMAP Progress Re-port 90-0497. Department of Geology, University of Texas at Ar-lington, Arlington, Texas, 45 pp.

———, and J. Golonka. 1993. Paleogeographic Atlas. PALEOMAPproject. University of Texas at Arlington, Arlington, Texas.

Sereno, P. C. 1998. A rationale for phylogenetic definitions, with ap-plication to the higher-level taxonomy of Dinosauria. Neues Jahr-buch fur Geologie und Palaontologie Abhandlungen 210:41–83.

——— 1999. The evolution of dinosaurs. Science 284:2137–2147.———, A. L. Beck, D. B. Dutheil, B. Gado, H. C. E. Larsson, G. H.


APPENDIX 1

Characters used in phylogenetic analysis.

All characters unordered.

Modified from Holtz, 1998, and references therein:1. Rostral ramus of maxilla: 0, present, rostrocaudal length of maxilla rostral to ascending ramus over ½ that of antorbital fenestra; 1, less than

½ length of antorbital fenestra.2. Promaxillary fenestra: 0, completely absent; 1, ovoid depression present in its place; 2, present, visible in lateral view; 3, present, obscured

in lateral view by lamina lateralis of maxillary ascending ramus.3. Interdental plates: 0, absent; 1, present and separate in the caudal portion of the maxilla; 2, present and completely fused.

Modified from Novas, 1992:4. Lamina medialis of maxillary ascending ramus: 0, strongly caudodorsally inclined, resulting in an angular rostral margin of the antorbital

fenestra; 1, subvertical, resulting in rounded rostral margin of the antorbital fenestra.

Modified from Martınez, et al., 1993:5. Tooth crown height to crown base length ratio of tallest fully erupted crown: 0, 2.0 or more; 1, 1.5 or less.

Modified from Coria and Salgado, 1995:6. Main body of maxilla: 0, rapidly decreasing in depth caudally; 1, maintaining depth throughout much of its length, with subparallel dorsal

and ventral margins. This was identified as an autapomorphy of the Argentine carcharodontosaurid Giganotosaurus carolinii by these authors.We found it to occur in several abelisaurids.

Modified from Sampson et al., 1996:7. Premaxillary articular surface: 0, angled strongly caudodorsally; 1, subvertical.

Sampson et al., 1998:8. Extensive sculpturing of maxillary lateral surface: 0, absent; 1, present.

Modified from Sereno, 1999:9. Short pre-orbital skull length. Maxillary length caudal to rostral margin of antorbital fenestra/depth caudoventral to base of lamina medialis:

0, 2.5 or more; 1, 2.0 or less.

Sereno, 1999:10. Maxilla-jugal contact, length: 0, short; 1; long and broad.

This work:11. Antorbital fossa on lateral surface of maxillary body: 0, present and well-developed; 1, strongly reduced or absent.

Description: In Coelophysis, the antorbital fossa is well-developed as a depression occupying much of the lateral maxillary surface. Itsmaximum rostroventral extent is clearly delineated by a pronounced lateral ridge (Colbert, 1989:figs. 38, 48). Ceratosaurus and Noasaurus displaya similar condition. In the abelisaurids Abelisaurus, Carnotaurus, Majungatholus, AMNH 1955, and UNPSJB-PV247 this ridge/depression complexhas been markedly reduced or is totally absent.

Lyon, J. D. Marcot, O. W. M. Rauhut, R. W. Sadleir, C. A. Sidor,D. J. Varricchio, G. P. Wilson, and J. A. Wilson. 1998. A long-snouted predatory dinosaur from Africa and the evolution of spi-nosaurids. Science 282:1298–1302.

———, D. B. Dutheil, M. Iarochene, H. C. E. Larsson, G. H. Lyon, P.Magwene, C. A. Sidor, D. J. Varricchio, and J. A. Wilson. 1996.Predatory dinosaurs from the Sahara and Late Cretaceous faunaldifferentiation. Science 272:986–991.

———, J. A. Wilson, H. C. E. Larsson, D. B. Dutheil, and H.-D. Sues.1994. Early Cretaceous dinosaurs from the Sahara. Science 266:267–270.

Smith, A. G., D. G. Smith, and B. M. Funnell. 1995. Atlas of Mesozoicand Cenozoic Coastlines. Cambridge University Press, Cambridge,99 pp.

Smith, J. B., and P. Dodson. In press. A proposal for a standard ter-minology of anatomical notation and orientation in fossil vertebratedentitions. Journal of Vertebrate Paleontology.

Sorenson, M. D. 1999. TreeRot, version 2. Boston University, Boston,Massachusetts.

Storey, M., J. J. Mahoney, A. D. Saunders, R. A. Duncan, S. P. Kelley,and M. F. Coffin. 1995. Timing of hot-spot related volcanism andthe breakup of Madagascar and India. Science 267:852–855.

Swofford, D. L. 2000. PAUP*. Phylogenetic Analysis Using Parsimony(*and Other Methods), Version 4.0b4a. Sinauer Associates, Sun-derland, Massachusetts.

Sues, H.-D. 1980. A pachycephalosaurid dinosaur from the Upper Cre-

taceous of Madagascar and its paleobiogeographical implications.Journal of Paleontology 54:954–962.

———, and P. Taquet. 1979. A pachycephalosaurid dinosaur from Mad-agascar and a Laurasia-Gondwanaland connection in the Creta-ceous. Nature 279:633–635.

Taquet, P., and D. A. Russell. 1998. New data on spinosaurid dinosaursfrom the Early Cretaceous of the Sahara. Comptes Rendus del’Academie des Sciences Parıs: Sciences de la terre et des planetes327:347–353.

Vallati, P. 1998. Palynology of the Huincul Formation (middle Creta-ceous) in the Neuquen Basin, Patagonia, Argentina. Abstracts ofthe SAMC 381 Third Annual Conference; pp. 30–32 in Boletin dela Asociacion Paleontologica del Golfo San Jorge (Edicıon espe-cial) 2.

Walker, A. D. 1964. Triassic reptiles from the Elgin area: Ornithosuchusand the origin of the carnosaurs. Philosophical Transactions of theRoyal Society, London, B 248:53–134.

Weishampel, D. B. 1990. Dinosaurian distribution; pp. 63–139 in D. B.Weishampel, P. Dodson, and H. Osmolska (eds.), The Dinosauria.University of California Press, Berkeley.

Witmer, L. M. 1997. The evolution of the antorbital cavity of archo-saurs: a study in soft-tissue reconstruction with an analysis of thefunction of pneumaticity. Society of Vertebrate Paleontology Mem-oir 3:1–73.

Received 19 July 1999; accepted 5 February 2001.


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A definitive abelisaurid theropod dinosaur from the early Late Cretaceous of Patagonia

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Transcript of A definitive abelisaurid theropod dinosaur from the early Late Cretaceous of Patagonia