Skull and neck of Carnotaurus sastrei (From Novas et al., 2013)
The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The oldest records of abelisauroid theropods are from the Early Jurassic. These ceratosaurian theropods exhibit spectacular cranial ornamentation in the form of horns and spikes; and strongly reduced forelimbs and hands. The group was erected by Jose Bonaparte with the description of Abelisaurus Comahuensis. Although represented by relatively well-known skeletons, the phylogenetic relationships within abelisaurids remain debated. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous, from Cenomanian (Ilokelesia, Xenotarsosaurus, and Ekrixinatosaurus) to Campanian–Maastrichtian (Abelisaurus, Carnotaurus, Aucasaurus, and Noasaurus).
Abelisauroidea has been divided into two main branches: the Noasauridae and the Abelisauridae. The Noasauridae are known from Cretaceous beds in northern Argentina, Madagascar, India, and Niger. They are small and slender with sizes that range from 1 to 3 metres in length. The best-preserved and most complete noasaurid is Masiakasaurus knopfleri from the Maastrichtian of Madagascar. The Abelisaurids are medium to large, robust animals, such as the Carnotaurus and the Majungasaurus of Madagascar. The group exhibits short, round snouts; thickened teeth; short, stocky arms; and highly reduced forearms.
Masiakasaurus on display at the Royal Ontario Museum.
Carnotaurus sastrei is the most advanced member of Abelisauridae. It was collected in the lower section of La Colonia Formation, Chubut Province, Argentina, by an expedition led by Argentinian paleontologist José Bonaparte. In 1985, Bonaparte published a note presenting Carnotaurus sastrei as a new genus and species and briefly describing the skull and lower jaw. The skull of Carnotaurus is complete, measuring 60 cm from the tip of the premaxillae to the distal tip of the paroccipital process. The most distinctive features of Carnotaurus are the two robust conical horns that extend from the frontals. The horns are dorsoventrally compressed, and 146 mm long on both sides. The dorsal surface of each horn is ornamented with a series of longitudinal grooves. Because relatively few abelisaurid braincases are known, the description of the Carnotaurus braincase is important for understanding the variability of this structure within the clade (Carabajal 2011). C. sastrei would have had a comparatively weak muscle-driven bite.
The forelimbs of Carnotaurus show an extreme reduction, proportionally greater than the reduction observed in tyrannosaurids, although the radius, ulna and humerus are very robust. The hand has four digits, including a large, conical-shaped metacarpal IV lacking an articulation for a phalanx.
References:
Novas, F.E., et al., Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia, Cretaceous Research (2013), http://dx.doi.org/10.1016/j.cretres.2013.04.001
Bonaparte, José F.; Novas, Fernando E.; Coria, Rodolfo A. (1990). “Carnotaurus sastrei Bonaparte, the horned, lightly built carnosaur from the Middle Cretaceous of Patagonia”, Contributions in Science (Natural History Museum of Los Angeles County) 416.
Mazzetta, Gerardo V.; Fariña, Richard A.; Vizcaíno, Sergio F. (1998). “On the palaeobiology of the South American horned theropod Carnotaurus sastrei Bonaparte”, Gaia 15: 185–192.
Ruiz, Javier; Torices, Angélica; Serrano, Humberto; López, Valle (2011). “The hand structure of Carnotaurus sastrei (Theropoda, Abelisauridae): implications for hand diversity and evolution in abelisaurids”. Palaeontology 54 (6): 1271–1277.
Letters from Gondwana. 