A juvenile allosauroid theropod (Dinosauria, Saurischia) from the Upper Jurassic of Portugal

Abstract

A new specimen of a theropod dinosaur found in Upper Jurassic sedimentary levels of the Lusitanian Basin (Portugal) is described. The specimen includes axial (cervical, dorsal, and caudal vertebrae and ribs) and pelvic elements, corresponding to a small-sized and juvenile individual. This specimen is one of the most complete theropod dinosaur from the Upper Jurassic of Portugal, and the only evidence of a post-hatchling juvenile theropod individual currently recognized in this record. The phylogenetic analysis recovered the new specimen as a basal Allosauroidea. It presents a combination of characters shared with other allosauroids already known in the Upper Jurassic of the Lusitanian Basin, Allosaurus and Lourinhanosaurus, but also some differences relative to both taxa. Some of these differences may be related to the juvenile condition of the specimen, but other unusual features cannot be properly explained by ontogeny, and are interpreted as having taxonomic significance. This combination of features might justify the description of a new theropod taxon for the Portuguese Upper Jurassic. Nevertheless, the presence of three sympatric and almost synchronic, closely related basal allosauroids requires further exploration of their intra- or interspecific variability.

Keywords:

• Allosauroidea
• Allosaurus
• Lourinhanosaurus
• Late Jurassic, Lusitanian Basin
• phylogenetic analysis

Acknowledgments

We thank to S. Brusatte and O. Rauhut for the comments and suggestions to the paper, to Willi Henning Society for the available free TNT program, to J. J. Santos, M. Cachão and N. Pimentel for field assistance and comments to the paper, to E. Cuesta for photographs of specimens, and for allow accessing specimens to Bruno. C. Silva (SHN), Rui Castanhinha and Carla Tomás (ML), Vanda Santos (MUHNAC), Ronan Allain (MNHN), Luis Chiappe (NHMLAC), Kenneth Carpenter (DMNH), Rodney Scheetz and Brooks Britt (BYU), Mike Getty, Mark Loewen, and Randall Irmis (NHMU), Daniel Chure (DINO), Sandra Chapman (NHMUK), and Paul Jeffery (OUMNH).