The anatomy of Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio and the interrelationships of thalattosaurs (Reptilia, Diapsida)

The anatomy of the thalattosauriform reptile Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio is redescribed. Important anatomical features are the plesiomorphic braincase, the unique fronto-lacrimal contact, the absence of a previously described thyroid fenestra, and significant intraspecific variation in the carpus. An analysis of thalattosaur ingroup relationships reveals that Endennasaurus and the monophyletic Askeptosaurus and Anshunsaurus are the sister group to all other thalattosaurs, whereas the Monte San Giorgio taxa Clarazia and Hescheleria form the sister clade of Thalattosaurus, and the Chinese Xinpusaurus and the Californian Nectosaurus form a monophyletic group. The analysis supports the biogeographic interpretation of trans-Pacific relationships and a re-invasion of Tethyan areas.