New theropod remains from Cerro Overo-La Invernada area (Bajo de la Carpa Formation, Santonian) from North Patagonia

MÉNDEZ, A.H.; VETTORAZZI, L.A.; SECULI-PEREYRA, E.; GONZÁLEZ-DIONIS, J.; GIANECHINI, F.A.; VALDÉZ, H.; PAULINA-CARABAJAL, A.; CÁRDENAS, M.; FILIPPI, L.S.; BARRIOS, F.; HEREDIA, A.M.; CRUZADO-CABALLERO, P.; RODRÍQUEZ-CANALIS, C.; FARÍAS-KLEPP, M.; GARRIDO, A.C.; LEE, Y.-N.; KWON, K.-D.

San Luis

Jornada; XXXVIII Jornadas Argentinas de Paleontología de Vertebrados; 2025

Comisión Organizadora XXXVIII Jornadas Argentinas de Paleontología de Vertebrados

The record of non-avian theropod dinosaurs identified from the Bajo de la Carpa Formation (Santonian, Upper Cretaceous) corresponds to remains of abelisauroids, megaraptorids, alvarezsaurids, and unenlagiines. In the Cerro Overo-La Invernada area, the remains of abelisaurids (which include two nominate taxa, Viavenator and Llukalkan) are the majority, although the presence of megaraptorids is well documented. In the last paleontological fieldwork (February 2025), new remains belonging to these two clades were recorded. For Abelisauridae, an isolated tooth, an incomplete right maxilla, and a complete left humerus were identified, while for Megaraptoridae, several medium to large vertebrae were found. The humerus (MAU-Pv-LI-737) measures 18.5 cm. The humeral head is not globose as in Carnotaurus, Majungasaurus, Aucasaurus, and Masiakasaurus, being more similar to Eoabelisaurus and MCF-PVPH 53. The deltopectoral crest and greater tubercle are not very developed and the internal tuberosity is separated from the humeral head by a poorly marked notch. The diaphysis is arched as in the rest of the abelisaurids but it differs because in its distal third shows a rotation that makes the ulnar condyle remain in an anteromedial position instead of medial. The tooth (MAU-Pv-LI-738) has the typical morphology of abelisaurids, with the distal carina almost straight and the mesial carina curved, with slightly hooked denticles present in both. The recovered maxilla (MAU-Pv-LI-739) is 15 cm long and has a maximum height of 7 cm, being slightly larger than that of Llukalkan and exhibits an ornamentation dominated by grooves and pits. The vertebral remains assignable to Megaraptoridae correspond to posterior dorsal vertebrae (MAU-Pv-LI-740 and 741) are characterized by the presence of large pneumatic foramina on the lateral surface of the centrum and a subcircular intervertebral articular surface. The ventral surface presents two parallel ridges that delimit a groove. The length of the vertebrae ranges between 7.7 and 10.5 cm, and the articular surfaces exceed 11.5 cm reaching 13 cm, both in height and width. These measurements are comparable to and even exceed those observed in the posterior dorsal vertebrae of the largest forms of megaraptorids known as Aerosteon, Tratayenia, Murusraptor, and Maip. The abundance and diversity of these new findings reinforce the idea that abelisaurids were the majority group of predators at least in the latest Cretaceous of northern Patagonia, but that they shared the top of the food chain with other larger theropods such as megaraptorids.