A juvenile sauropodomorph tibia from the ‘botucaraí hill’, late triassic of Southern Brazil

Abstract

The ‘Botucaraí Hill’ outcrop yielded a diverse Late Triassic vertebrate fauna, including several dinosaur remains, but most collected specimens are represented only by isolated bones. We present here a new dinosaur tibia from that site, particularly notable for its small size. Anatomical comparisons and a phylogenetic analysis support a sauropodomorph affinity for the specimen. In addition, histological analyses on transverse sections of the tibial shaft revealed a very thin bone wall, characterized by woven matrix with high vascularization, and the complete absence of lines of arrested growth (LAGs). These features suggest that the specimen was undergoing rapid and uninterrupted bone growth prior to death. Indeed, the small size of the specimen, the poor ossification of the bone extremities, and the absence of LAGs indicate that it represents a juvenile individual, as not previously recorded for the Brazilian Upper Triassic dinosaur fauna.