Rostral morphology of Spinosauridae (Theropoda, Megalosauroidea): premaxilla shape variation and a new phylogenetic inference

Spinosauridae presents an extensive geographical and temporal distribution, with records from Gondwana and Laurasia, and a temporal range from Barremian (similar to 129 Ma, Lower Cretaceous) to Cenomanian (similar to 95 Ma, Upper Cretaceous). To date, 13 species were described, besides several specimens identified at a broader taxonomic level. One of the most notable cranial features of spinosaurids is their elongated rostrum (hypertrophied premaxilla-maxilla). Leastwise five species possess preserved premaxillae: Angaturama limai, Baryonyx walkeri, Cristatusaurus lapparenti, Oxalaia quilombensis and Suchomimus tenerensis, besides materials tentatively attributed to Spinosaurus aegyptiacus. We studied the premaxillae shape of 10 specimens of the above-mentioned species and other materials through geometric morphometrics, reviewing diagnoses and morphological descriptions. Clear allometric and phylogenetic signals could be identified by ordination methods. We carried out a phylogenetic analysis to test spinosaurid relationships, by inclusion of new landmarks-characters from the premaxillae into a published tetanuran character-taxon matrix. The phylogenetic inference recovered C. lapparenti outside Baryonychinae, which was composed by B. walkeri and S. tenerensis. Spinosaurinae was recovered as (A. limai, (O. quilombensis, (MSNM V4047, Irritator challengeri))). Our results suggest that the premaxillae provide useful phylogenetic information and that the inclusion of landmarks-characters improves our knowledge of this enigmatic clade.