New fossil remain of a juvenile elasmarian ornithopod from the Santonian of the Bajo de la Carpa Formation

GONZÁLEZ-DIONIS, JAVIER; CRUZADO-CABALLERO, PENÉLOPE; FILIPPI, LEONARDO S.; MÉNDEZ, ARIEL H.

Trelew

Jornada; XXXV Jornadas Argentinas de Paleontología de Vertebrados; 2022

Museo Egidio Feruglio

Mahuidacursor lipanglef (MAU-Pv-CO-596) was an ornithopod that were found in the Cerro Overo-La Invernada area, in the Bajo de la Carpa Formation (Santonian, Upper Cretaceous) near what is now Rincón de los Sauces (Neuquén province), in an exceptional state of preservation. Among them, the almost complete right arm (humerus, radius and ulna) was excavated. Also, numerous remains identified as indeterminate ornithopods have been found in the same area. These bones pertain to several individuals of different ontogenetic stages, including juveniles. Here we described a new humerus (MAU-Pv-CO-654) which could belong to a juvenile or sub-adult specimen of M. lipanglef. MAU-Pv-CO-654 has a gracile appearance and presents characteristics that relate it to the Elasmaria clade and to M. lipanglef, such as the scarce development of the deltopectoral crest. It also has a very bowed shaft, a characteristic it shares with basal and derived ornithopods (i.e. elasmaria). The proximal end is slightly lateromedially extended, being wider than the distal end. As for the distal end, the condyles are subequal. The morphological characteristics that indicate that MAU-PV-CO-654 would be a juvenile or sub-adult specimen are: a) poorly marked muscle markings in the lateral region of the deltopectoral crest; b) low degree of ossification, both at the proximal, distal ends and in the shaft; and c) its length is 24% shorter than that of the humerus of M. lipanglef. In MAU-Pv-CO-654, the bowing of the humeral diaphysis is slightly more pronounced than in the humerus of M. lipanglefbeing a probable case of individual varibility as in other ornithopods. Based on its characteristics it could be classified as juvenile cf. Mahuidacursor, in the absence of further comparative materials being found.