New abelisaurid (Dinosauria, Theropoda) remains from Cerro Overo (Bajo de la Carpa Formation), northern Neuquén, Patagonia, Argentina

MÉNDEZ, ARIEL H.; PAULINA-CARABAJAL, ARIANA; FILIPPI, LEONARDO S.; GIANECHINI, FEDERICO A.; CRUZADO-CABALLERO, PENÉLOPE; PREVITERA, MARÍA ELENA; BARRIOS, FRANCISCO; SECULI PEREYRA, E. EMANUEL; GARRIDO, ALBERTO C.; PIPO, LAURA

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 fibula,right metatarsal III, left metatarsal IV, a probable left metatarsal V, plus several pedal phalanges. The maxilla, poorlypreserved, has the typical external ornamented surface of abelisaurids (e.g., Skorpiovenator, Tralkasaurus), and a markedanterior process as in Majungasaurus, different from the short process of Carnotaurus, Llukalkan, and Skorpiovenatoror thealmost non-existent process of Aucasaurusand Ekrixinatosaurus. The posterodorsal inclination of the ascending process issimilar to that of Aucasaurusand Majungasaurus, and the contact with the jugal seems to have a more inclined angle, as inSkorpiovenator. The femur has a well-marked abductor fossa, a moderately developed mediodistal crest, and a reducedlateral prominence. The tibia shows, in proximal view, the typical comma-shape, with a conspicuous groove between themedial 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 fibulaexhibits a fibular fossa much extended on the medial surface, different from that of Viavenatorin 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 anterodistalfossa, probably for insertion of M. extensor digitorum longus, and an anteromedial ridge on the distal half, as inMajungasaurus. The Mt IV shows, in anterior view, a pronounced lateral curvature in the distal half, as in Majungasaurusbutunlike the straighter Mt IV of Aucasaurus. In distal view, the intercondylar groove is less marked than in AucasaurusandMajungasaurus. The first three phalanges of the fourth pedal digit were articulated next to the metatarsal. Pedal phalanxIV-1 is short and robust, similar to that in Majungasaurusbut unlike the longer phalanx of Aucasaurus. The second phalanxis slightly shorter than the first, as in Aucasaurusalthough conversely to the condition observed in Majungasaurus, andshows a marked dorsoproximal projection. Pedal phalanx IV-3 is similar in length to the previous one, as in AucasaurusandMajungasaurus. The three phalanges show, in dorsal view, a more marked lateral concavity than that observed inMajungasaurusand Aucasaurus. The phylogenetic position of this specimen within Abelisauridae is still unclear and dependson the exhumation of the remaining materials from the field; however, it shows a mixture of features present in bothmajungasaurines and brachyrostrans. Also, the differences with the maxilla and tibia of the other abelisaurids from this area(Viavenatorand Llukalkan) suggest this specimen may represent a new taxon. This is the seventh abelisaurid specimenrecovered from this site, which not only increases the knowledge about these theropods but also supports the presenceof mid-sized abelisaurids as main carnivorous dinosaurs in the Santonian ecosystems of northern Patagonia.