NEW ABELISAURID (DINOSAURIA, THEROPODA) REMAINS FROM CERRO OVERO (BAJO DE LA CARPA FORMATION), NORTHERN NEUQUÉN, PATAGONIA, ARGENTINA

ARIEL MÉNDEZ; ARIANA PAULINA-CARABAJAL; LEONARDO FILIPPI; FEDERICO GIANECHINI; PENÉLOPE CRUZADO-CABALLERO; ELENA PREVITERA; FRANCISCO BARRIOS; EMANUEL SECULI PEREYRA; ALBERTO GARRIDO; LAURA PIPO

Buenos Aires

Congreso; XII Congreso de la Asociación Paleontológica Argentina; 2021

Asociación Paleontológica Argentina

We report here new abelisaurid remains (MAU-PV-CO-661; Museo Argentino Urquiza, Paleovertebrados, Cerro Overo) recovered from Cerro Overo, including: left maxilla, distal end of left femur, articulated proximal ends of left tibia and fi bula, right metatarsal III, left metatarsal IV, a probable left metatarsal V, plus several pedal phalanges. The maxilla, poorly preserved, has the typical external ornamented surface of abelisaurids (e.g., Skorpiovenator, Tralkasaurus), and a marked anterior process as in Majungasaurus, different from the short process of Carnotaurus, Llukalkan, and Skorpiovenator or the almost non-existent process of Aucasaurus and Ekrixinatosaurus. The posterodorsal inclination of the ascending process is similar to that of Aucasaurus and Majungasaurus, and the contact with the jugal seems to have a more inclined angle, as in Skorpiovenator. The femur has a well-marked abductor fossa, a moderately developed mediodistal crest, and a reduced lateral prominence. The tibia shows, in proximal view, the typical comma-shape, with a conspicuous groove between the medial and lateral condyles, as in Xenotarsosaurus, Aucasaurus, and Carnotaurus. The cnemial crest has the axe-shaped formpresent in other abelisaurids, but with a highly marked distal end as in Quilmesaurus, Aucasaurus, and Genusaurus. The fibula exhibits a fibular fossa much extended on the medial surface, different from that of Viavenator in which is less developed, and its outline is subrectangular in proximal view, different from the comma-shape observed in Aucasaurus, Xenotarsosaurus, and Majungasaurus. The Mt III has an almost straight diaphysis along its entire length, and bears a conspicuous anterodistal fossa, probably for insertion of M. extensor digitorum longus, and an anteromedial ridge on the distal half, as in Majungasaurus. The Mt IV shows, in anterior view, a pronounced lateral curvature in the distal half, as in Majungasaurus but unlike the straighter Mt IV of Aucasaurus. In distal view, the intercondylar groove is less marked than in Aucasaurus and Majungasaurus.The first three phalanges of the fourth pedal digit were articulated next to the metatarsal. Pedal phalanx IV-1 is short and robust, similar to that in Majungasaurus but unlike the longer phalanx of Aucasaurus. The second phalanx is slightly shorter than the first, as in Aucasaurus although conversely to the condition observed in Majungasaurus, and shows a marked dorsoproximal projection. Pedal phalanx IV-3 is similar in length to the previous one, as in Aucasaurus and Majungasaurus. The three phalanges show, in dorsal view, a more marked lateral concavity than that observed in Majungasaurus and Aucasaurus. The phylogenetic position of this specimen within Abelisauridae is still unclear and depends on the exhumation of the remaining materials from the field; however, it shows a mixture of features present in both majungasaurines and brachyrostrans. Also, the differences with the maxilla and tibia of the other abelisaurids from this area (Viavenator and Llukalkan) suggest this specimen may represent a new taxon. This is the seventh abelisaurid specimen recovered from this site, which not only increases the knowledge about these theropods but also supports the presence of mid-sized abelisaurids as main carnivorous dinosaurs in the Santonian ecosystems of northern Patagonia.