Archosauriform endocranial morphology and osteological evidence for semiaquatic sensory adaptations in phytosaurs
· 1 Specimen
· Managed by: Lessner Emily
The examination of endocranial data of archosauriforms has lead to advances on the evolution of body size, nerve pathways, and sensory abilities. However, much of that research has focused on bird-line archosaurs, resulting in a skewed view of Archosauria. Phytosauria, a suggested sister taxon of Archosauria, provides a potential outgroup condition. Most previous phytosaur endocranial studies were executed without the use of modern technology and focused on derived taxa. We provide a comparative CT examination of the internal cranial anatomy of Wannia scurriensis, currently the most basal known phytosaur, providing a potential representative for the ancestral archosaur endocranial morphology. Wannia scurriensis shows some overall similarity with extant crocodylians and derived phytosaurs in general endocranial shape, a large hypophyseal fossa, and trigeminal (CN V) innervation, but as a whole, the endocast has noticeable differences to crocodylians and other phytosaurs. The pineal region is expanded dorsally as in other phytosaurs but also laterally (previously unrecognized). CN V exits the pons in a more dorsoventral position than in Parasuchus hislopi, Machaeroprosopus mccauleyi, or Smilosuchus gregorii. Wannia scurriensis also exhibits a larger hypophyseal fossa relative to brain size than observed in P. hislopi or S. gregorii, which may indicate more rapid growth. The well-preserved semicircular canals have lateral canals that are angled more anteroventrally than in the derived taxa. Extensive facial innervation from the large CN V suggests increased rostrum sensitivity and mechanoreceptive abilities as in Alligator mississippiensis. These endocranial similarities among phytosaurs and with Alligator indicate conserved ecological and functional results of an aquatic lifestyle, and highlight a need for further exploration of endocranial anatomy among Archosauriformes.