Introducing Llukalkan aliocranianus

Photograph of the materials in the field. Image credit: Federico Gianechini

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 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 Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Tralkasaurus cuyi and Viavenator exxoni. Llukalkan aliocranianus, a new furileusaurian abelisaurid from the Bajo de la Carpa Formation (Santonian) in northwestern Patagonia, is an important addition to the knowledge of abelisaurid diversity.

 

Reconstruction of the complete skull and mandible of Llukalkan aliocranianus. Scale bar: 5 cm. From Gianechini et al., 2021

The new specimen was found near the site where the remains of Viavenator exxoni were recovered at La Invernada fossil area, 50 km southwest of Rincón de los Sauces city, Neuquén province, Argentina. This site has provided a valuable theropod record. Other taxa discovered at La Invernada include the titanosaurian sauropods Bonitasaura salgadoi, Traukutitan eocaudata, and Rinconsaurus caudamirus, pterosaurs, multiple crocodyliforms, snakes, and turtles.

The holotype (MAU-Pv-LI-581) is an incomplete but partially articulated skull with a complete braincase. The generic name derived from the word Llukalkan, “one who scares or causes fear” in Mapudungun language. The specific name aliocranianus means “different skull” in Latin.  Llukalkan exhibits some similarities with Viavenator, that include: elongate and robust olfactory tracts; large and horizontally oriented olfactory bulbs; cerebral hemispheres clearly delimited in lateral view; a tongue-shaped floccular process of cerebellum posteriorly projected and reaching the level of the posterior semicircular canal; and elongate and ventrally projected passage for the rostral middle cerebral vein. Additionally, Llukalkan has a small pneumatic recess caudal to the columellar recess, which is identified as a poorly developed caudal tympanic recess. This taxon also presents a T-shaped lacrimal with jugal ramus lacking a suborbital process, that differs significantly from the lacrimal of other abelisaurids.

 

References:

Federico A. Gianechini, Ariel H. Méndez, Leonardo S. Filippi, Ariana Paulina-Carabajal, Rubén D. Juárez-Valieri & Alberto C. Garrido (2021): A New Furileusaurian Abelisauridfrom La Invernada (Upper Cretaceous, Santonian, Bajo De La Carpa Formation), NorthernPatagonia, Argentina, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2020.1877151