A NEW BRACHYROSTRAN ABELISAURID (THEROPODA, CERATOSAURIA) FROM THE PORTEZUELO FORMATION (UPPER CRETACEOUS) OF PATAGONIA, ARGENTINA

BAIANO, M.A.; POL D.; BELLARDINI, F.; WINDHOLZ G.J.; CERDA, I.A.; GARRIDO, A.C.; CORIA, R.A.

Congreso; XXV Jornadas argentinas de paleontología de vertebrados; 2022

Abelisaurids are medium-to-large sized theropod dinosaurs that outweighed the carnivorous faunaeduring the Late Cretaceous of Gondwana. These predators are specially abundant in the Cretaceousfossil strata of Patagonia, which hold the best record for this group. Despite the possible MiddleJurassic origin of Abelisauridae, the first definitive forms are known from the Early Cretaceous ofArgentina, Brazil and Africa. Later on, although abelisaurids appear in almost all beds of the LateCretaceous of Gondwana, they are virtually wordlwide unknown for the Coniacian strata. Here wedescribe a new abelisaurid specimen (MCF-PVPH-380), from the Turonian-Coniacian PortezueloFormation, Patagonia, Argentina. MCF-PVPH-380 is based on several axial and appendicularelements, and shows some distinctive features such as a peculiar pattern of rugosities on the lateral surface of the fibula, and a calcaneum with a dorsoventrally deep lateral wall. Furthermore, the posterior caudal vertebrae (some of these affected by pathological processes) show a slightlydifferent morphology from any other abelisaurid. The microstructural features of the appendicularbones of MCF-PVPH-380 show the specimen was a subadult individual at the time of its dead, buthad achieved sexual maturity. MCF-PVPH-380 is recovered as an unstable taxon within Brachyrostra, either as a sister taxon of the Furileusauria or in several positions within this clade. Despite their phylogenetic relationships, MCF-PVPH-380 represents the first abelisaurid record recognized from the Turonian-Coniacian interval, increasing the diversity of this theropod clade at the time of a South American tetrapod turnover, global climate change, and mass extinction events recorded worldwide in the marine realm.