The basal mosasaurid Halisaurus sternbergii from the Late Cretaceous of Kansas (North America): a review of the Uppsala type specimen

The type specimen of Clidastes sternbergii Wiman, 1920, a basal mosasaurid from the Santonian of Kansas (USA), is reviewed. Its attribution to Halisau rus is confirmed. H. sternbergii is mainly defined on the basis of cranial characters: frontal with a smooth dorsal surface bearing a prominent median ridge; parietal with a triangular table extending far posteriorly and bear ing a medium sized circular foramen, which is located at a distance equal t o twice its diameter from the frontal-parietal suture. The vertebral column and appendicular skeleton retain many plesiomorphies. H. sternbergii is th e oldest species of the genus, also known in the Maastrichtian. (C) 2001 Ac ademie des sciences / Editions scientifiques et medicales Elsevier SAS.