Morphology and neurovascular patterns of the premaxillary bones of the Abelisauridae

SOUZA JUNIOR, A.L.; PAULINA CARABAJAL, A.; CANDEIRO, C.R.A.

Rio de Janeiro

Simposio; X Simposio Brasileiro de Paleontología de Vertebrados; 2016

Museu Nacional-Universidade Federal do Rio de Janeiro

The Abelisauridae is one of the most characteristic groups of South American dinosaurs. They originated in the Jurassic and reached their apogee of diversity in the Late Cretaceous, when they were diverse across Gondwana. Over the past d cade the phylogenetic relationships of abelisaurids have been widely studied and much progress has been made in understanding the evolution of the group. One particularly important bone in phylogenetic studies is the premaxilla, which preserves several critical characters of taxonomic significance. For example, ceratosaurs are diagnosed by a craniocaudal shortening of the premaxilla, in which the bone is higher dorsoventrally than long anteroposteriorly.Another important character of taxonomic  alue is the absence of the premaxillary palatalprocess. Here we survey the morphology of the premaxilla among abelisaurids and describe the variation in the neurovascular system, particularly the position and size of neurovascular foramina. Below the nasal process of the premaxilla there is a neurovascular foramen in Majungasaurus crenatissimus and Rahiolisaurus gujaratensis, located further ventrally than in large allosauroids (e.g., Sinraptor dongi and Allosaurus fragilis). Also, the abelisaurid neurovascular foramina are smaller than in other middle-large size theropods (e.g.,allosauroids, spinosaurids and tyrannosaurids), demonstrating that the position and size of the neurovascular foramina are variable among large theropod taxa. The ventral position and smaller size of the neurovascular foramen could be a diagnostic character of abelisaurids, which would be important in phylogenetic analyses, but the function and paleobiological implications of the associated nerves and blood vessels need to be tested. Further study of abelisaurid fossils will allow a better understanding of their premaxillary morphologies and help to evaluate this hypothesis.