Abelisauridae Bonaparte and Novas, 1985

Rauhut, Oliver W. M., 2003, The interrelationships and evolution of basal theropod dinosaurs, Special papers in palaeontology 69, pp. 1-213 : 33-34

Abelisauridae Bonaparte and Novas, 1985

Included taxa. Abelisaurus comahuensis Bonaparte and Novas, 1985 ; Camotaurus sastrei Bonaparte, 1985 ; Genusaurus sisteronis Accarie, Beaudoin, Dejax, Friès, Michard and Taquet, 1995 ; Ilokelesia aguadagrandensis Coria and Salgado, 2000 ; Indosuchus raptorius Huene, 1932 ; Majungatholus atopus Sues and Taquet, 1979 ; Masiakasaurus knopfleri Sampson, Carrano and Forster, 2001 ; Noasaurus leali Bonaparte and Powell, 1980 ; Xenotarsosaurus bonapartei Martinez, Giménez, Rodriguez and Bochatey, 1986

Temporal range. Albian-Maastrichtian.

Occurrence. Allen Formation, Rio Negro, Argentina; La Colonia Formation, Chubut, Argentina; unnamed unit (green clays and glauconitic sands of Bevons), Alpes de Haute-Provence, France; Lameta Formation, Madhya Pradesh, India; Maevarano Formation, Majunga, Madagascar; Lecho Formation, Salta, Argentina; Bajo-Barreal Formation, Chubut, Argentina.

Diagnosis. Maxilla in front of the antorbital opening very short and high; posterior border of lacrimal convex over its entire length; anterior process of lacrimal reduced; jugal process of postorbital expanded, strongly anteriorly directed and intrudes into the orbit (convergently present in Tarbosaurus bataar and Tyrannosaurus rex , but not in other tyrannosaurids); epipophyses in the cervical vertebrae hypertrophied and higher than the neural spines.

Remarks. Abelisaurids have recently been recognized as a distinct family of theropod dinosaurs (Bonaparte and Novas 1985). Their diagnosis and taxonomy is still problematic, mainly due to the fragmentary nature of the remains of all members of the family with the exception of Camotaurus ( Bonaparte et al. 1990) and recently described new specimens of Majungatholus (Sampson et al. 1998) . Given the many peculiarities in the skeleton of these genera, it seems very probable that the discovery of more complete material of other taxa will provide more diagnostic characters for this family.

Camotaurus sastrei ( Text-fig. 6a ), Majungatholus atopus , and Abelisaurus comahuensis share all of the cranial synapomorphies listed above, and so their referral to the Abelisauridae is well supported. However, many other, very incompletely known taxa have been assigned to this family ( Martinez et al. 1986; Bonaparte et al. 1990; Molnar 1990; Bonaparte 1991 b; Le Loeuff and Buffetaut 1991), and many of these assignments are problematical. Therefore, a short review of poorly known taxa that are included in the Abelisauridae here is given below.

Noasaurus leali was originally assigned to its own family, Noasauridae (Bonaparte and Powell 1980) . Later, Bonaparte (1991 /?) noted the close similarities between Noasaurus and abelisaurids and created the superfamily Abelisauroidea to include these two families ( Bonaparte 1991 /?, p. 22). Noasaurus shares the first diagnostic character with Abelisaurus, Carnotaurus , and Majungatholus , and the fifth character with Carnotaurus and Majungatholus , and may therefore be regarded as a close relative of these taxa. Since the differences between the Noasauridae and Abelisauridae , as defined by Bonaparte (1991 /?), are only slight and may partly reflect size-dependant and/or ontogenetic differences, the recognition of two families is not accepted here. Although Coria and Salgado (2000) presented a cladogram of neoceratosaurs supporting the distinction of noasaurids and abelisaurids, their results must be seen as preliminary since only some taxa of the Abelisauria were included, characters were restricted to synapomorphies defining each node, and the majority of abelisaurid taxa considered in this analysis are known from less than 20 per cent of the skeleton. A more inclusive analysis might yield quite different results; therefore, all abelisaurs known are included in a single clade, Abelisauridae , here. However, apart from Noasaurus , the recently described Masiakasaurus also indicates an important diversity of small abelisaurids ( Sampson et al. 2001).

Although based on very fragmentary material, Ilokelesia aguadagrandensis can be demonstrated to be an abelisaur with some certainty, since it shares the pecularities of the postorbital and the hypertrophied cervical epipophyses with other abelisaurid taxa ( Coria and Salgado 2000).

Indosuchus raptorius was described by Huene (1932) and Huene and Matley (1933) on the basis of a posterior end of a skull roof from the Maastrichtian Lameta Formation of India, and more material was later referred to this taxon ( Chatterjee 1978; Chatterjee and Rudra 1996). Sometimes considered to be a tyrannosaurid ( Chatterjee 1978; Paul 1988 «), Indosuchus has recently been placed in the Abelisauridae by several authors (Bonaparte and Novas 1985; Buffetaut et al. 1988; Bonaparte et al. 1990; Bonaparte 1991 /?). Since there seem to be several large theropods in the Lameta Formation, the material referred to Indosuchus by Chatterjee (1978) cannot be shown to represent this taxon with certainty ( Molnar 1990). However, the type specimen shows the same arrangement of the supratemporal fenestrae as found in Abelisaurus , Majungatholus , and Carnotaurus ; thus, this species is referred to the Abelisauridae .

Genusaurus sisteronis was described as a ceratosaurian theropod by Accarie et al. (1995) on the basis of several vertebrae and an incomplete pelvis and hindlimb. Genusaurus clearly represents a valid taxon, based on the peculiar morphology of the anterior end of the ilium ( Accarie et al. 1995, fig. 4a; the anterior end of this element seems to be lacking only minor parts, and its overall morphology is real, not a result of preservation; Carrano, pers. comm. 1999). Although none of the diagnostic characters of the abelisaurids is evident from the published illustrations, Genusaurus is referred here to this clade, since it shares two apomorphic characters with Carnotaurus : the almost completely straight dorsal margin of the ilium, and the very long and vertically oriented ischial peduncle of the ilium. These characters are not present in an ilium of Majungatholus (UA 8678; Sampson et al. 1998, fig. 2f), indicating that, within abelisaurids, Genusaurus may be more closely related to Carnotaurus than to Majungatholus .

Xenotarsosaurus is based on a dorsal vertebra and hindlimb elements, including femur, tibia, fibula, and astragalocalcaneum, from the Upper Cretaceous of Argentina ( Martinez et al. 1986). Although none of the diagnostic characters of the family as diagnosed here is found in the holotype, the taxon is tentatively referred to the Abelisauridae , based on the great overall similarity of the preserved elements to the comparable elements of Carnotaurus .

The recently described supposed abelisaurid Tarascosaurus salluvicus Le Loeuff and Buffetaut, 1991 , from the Upper Cretaceous of southern France, is based on extremely fragmentary material that does not show any diagnostic characters and is, therefore, regarded as a nomen dubium. However, the presence of abelisaurids in the Upper Cretaceous of southern Europe is also supported by other material ( Buffetaut et al. 1988).

Figures

text-fig. 6. Skull reconstructions of representatives of Cretaceous OTUs in left lateral view, a, abelisaurid Camotaurus sastrei, Late Cretaceous (Campanian), Gorro Frigio Formation, Argentina; based on Bonaparte et al. (1990) and MACN CH 894. b, composite skull of a generalized baryonychid; mainly based on Suchomimus tenerensis (MNN GDF 501, 503-506) and Irritator challenged (SMNS 58022), with some elements reconstructed after Baryonyx walkeri (BMNH R 9951). c, carcharodontosaurid Carcharodontosaurus sahariens, Late Cretaceous (Cenomanian), Kem Kem beds, Morocco; based on Sereno et al. (1996) and SGM-Din 1, unpreserved elements shaded. D, dromaeosaurid Velociraptor mongoliensis, Late Cretaceous (Campanian), Djadokhta Formation, Mongolia; based on Barsbold (1983), Barsbold and Osmólska (1999), and AMNH 6515. e, ornithomimosaur Dromiceiomimus brevitertius, Late Cretaceous (Maastrichtian), Horseshoe Canyon Formation, Alberta, Canada; redrawn from Russell (1972). F, oviraptorosaur Oviraptor philoceratops, Late Cretaceous (Campanian), Djadokhta Formation, Mongolia; redrawn from Barsbold et al. (1990). G, therizinosauroid Erlikosaurus andrewsi, Late Cretaceous (Cenomanian- Turonian), Baynshiren Svita, Mongolia; based on Clark et al. (1994). H, tyrannosaurid Gorgosaurus libratus, Late Cretaceous (Campanian), Judith River Formation, Alberta, Canada, redrawn from Molnar et al. (1990). Abbreviations as in Text-figures 4 and 5, and: acc. op., accessory opening of unknown function in the premaxilla of Oviraptor (Barsbold et al. 1990); amf, anterior maxillary foramen; pn, pneumatic openings. Scale bars represent 50 mm (d-g) and 100 mm (a-c, h).