Caracterización osteológica y ontogenética de un ejemplar juvenil de un saurópodo Titanosaurio

Abstract

Neuquensaurus australis is a taxon with a long history, it´s one of the first dinosaurs described in Argentina. Even so, only recently a juvenile has been reported for this species. Here I describe the specimenMCS-Pv174-41/66/68/77/78 composed by a vertebral dorsal centrum, vertebral caudal centrum, right scapula and fibula and the left coracoid. These materials were first reported by Zurriaguz et al. in 2019 and identified as N. australis thanks to diagnostics characters in the fibula and the caudal centrum. I compared this specimen with other titanosaurs to validate its taxonomic designation and to identify the variations throughout ontogeny. Phylogenetic analysis results in a polytomy with other saltasaurids, including N. australis, the main differences with other specimens being the lack of some pneumatic indicator features. To estimate its ontogenetic stage, the small size of the material was taken into account. The relationship of the robustness index (IR) was considered to infer an isometric growth, at least in its appendicular skeleton. The absence of fusion at the neurocentral suture is an indication of immaturity, but the complexity of its morphology could be related to later ontogenetic stages, it could also be an indication of a mechanical stress adaptation. Following the ontogenetic morphological stages (MOS) criteria for the axial skeleton, the caudal centrum MCS-Pv174/66 is considered MOS3 and dorsal centrum MCS-Pv174/41 MOS2. This specimen could be considered in a late immature stage, it didn´t reach 60% the full size of the largest N. australis that have been described and it lacks evidence of internal invasion of pneumatic diverticula inside the skeleton. This could mean that the characteristic high pneumatic profile of the group could be reached in the late immature stage or after reaching maturity.