Photo: AFP/MUSEO ARGENTINO DE CIENCIAS NATURALES
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 group was erected by the legendary paleontologist Jose Bonaparte with the description of Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Eoabelisaurus mefi and Viavenator exxoni.
Abelisauroids were traditionally divided into two main clades: large-sized Abelisauridae, and small-sized Noasauridae. 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. Now, a new abelisaurid from the upper section of the Huincul Formation (Cenomanian-Turonian) at the Violante Farm fossil site, Río Negro province, northern Patagonia, Argentina, is an important addition to the knowledge of abelisaurid diversity.
Map of El Cuy region showing the Violante farm fossil site. From Cerroni et al., 2020.
The holotype MPCA-Pv 815 is represented by an incomplete specimen including a right maxilla, distorted and incomplete dorsal, sacral and caudal vertebrae, cervical ribs, and pubis. Tralkasaurus is a medium-sized abelisaurid, much smaller than large abelisaurids as Abelisaurus and Carnotaurus. The name derived from Tralka, thunder in Mapudungun language, and saurus, lizard in Ancient Greek. The specific name “cuyi” derived from the El Cuy, the geographical area at Rio Negro province, Argentina, where the fossil was found.
This four-meter-long (13-foot-long) theropod exhibits a unique combination of traits, including deeply incised and curved neurovascular grooves at the lateral maxillary body that originate at the ventral margin of the antorbital fossa, and shows an extensive antorbital fossa over the maxillary body that is ventrally delimited by a well-marked longitudinal ridge that runs from the promaxillary fenestra level towards the rear of the maxilla.
Because body mass is usually indicative of an ecological niche, the new taxon probably occupied a different ecological niche within the predatory guild.
References:
Cerroni, M.A., Motta, M.J., Agnolín, F.L., Aranciaga Rolando, A.M., Brissón Egli, F., & Novas, F.E. (2019). A new abelisaurid from the Huincul Formation (Cenomanian-Turonian; Upper Cretaceous) of Río Negro province, Argentina. Journal of South American Earth Sciences https://www.sciencedirect.com/science/article/abs/pii/S0895981119304766
Letters from Gondwana. 