The internal cranial anatomy of Champsosaurus lindoei and its functional implications

AlthoughChampsosaurusis well-known in Late Cretaceous and Paleocene deposits of North America, their cranial anatomy is poorly understood. Here, a well-preserved skull ofChampsosaurus lindoeiis described in detail using high-resolution micro-CT scanning. This confirms the presence of the putative neomorphic bone, which may be homologous with the pre-existing stapes, or developed through incomplete fusion of dermatocranial ossification centres. The ventral openings on the skull ofChampsosaurusrelate to the fenestrae ovales, an unusual configuration that may be convergent with other aquatic reptiles. Overall, the endocranial anatomy ofChampsosaurusis typical for a basal diapsid. The morphology of the pars inferior of the inner ear suggests thatChampsosauruswere capable of detecting sound underwater, and geometric morphometric analyses of the semicircular canals suggests that they were specialized for detecting head movements in an aquatic environment. Taken together, these results suggest thatChampsosauruswere well adapted for an aquatic lifestyle.