Phylogenetic relationships of Mussaurus patagonicus (Dinosauria, Sauropodomorpha) del Triásico Superior de Patagonia, Argentina

ALEJANDRO OTERO; DIEGO POL

Ciudad Autónoma de Buenos Aires

Jornada; XXVI Jornadas Argentinas de Paleontología de Vertebrados; 2012

Fundación de Historia Natural Félix de Azara

Mussaurus patagonicus Bonaparte and Vince is a basal sauropodomorph from the Late Triassic Laguna Colorada Formation (Santa Cruz Province, Argentina). This taxon is known from different ontogenetic stages, including hatchlings, juveniles, and adult individuals, but its affinities within Sauropodomorpha remain unclear. Previous cladistic analyses include either only information from juvenile specimens or a mixture of scorings from juvenile and adult specimens, which can lead to different results than using only the information from adult specimens. New phylogenetic information of this taxon is presented here based on the postcranial skeleton of adult individuals of Mussaurus collected during 1960s, housed at the Museo de La Plata (MLP 68-II-27-1, MLP 61-III-20-22, MLP 61-III- 20-23) and Museo de Buenos Aires (MACN-SC 3379). The characters scored were based solely on adult individuals, and a new character was added to a previously published dataset, summing up a data matrix of 362 characters and 53 taxa. All MPTs depict Mussaurus patagonicus as a basal member of Anchisauria, being the sister group of the clade composed by Aardonyx plus more derived sauropodomorphs. The phylogenetic position of M. patagonicus depicted here is supported, among others, by the following characters: fourth trochanter represented by a tall crest, fibular trochanter laterally facing, and well developed brevis fossa with sharp margins on the ventral surface of the postacetabular process of the ilium. This new interpretation of the phylogenetic position of M. patagonicus differs with previous hypothesis that regarded Mussaurus as a basal member of Sauropodomorpha (together with Thecodontosaurus and Efraasia).