Pachystropheus  Pachystropheus (After Greek "Pachys", "Thick" and "Strophaios", Vertebrae) is a genus of prehistoric reptile, possibly a choristodere (champsosaur), from the Rhaetian (Late Triassic) of southwestern England. It was named by Erika von Huene in 1935; Huene described "Pachystropheus" as a champsosaur, but this was overlooked for decades until its redescription by Storrs and Gower in 1993. This reevaluation would extend the fossil record of champsosaurs back 45 million years. However, other authors consider attribution of "Pachystropheus" to Choristodera problematic, stating that it depends on vertebral and girdle characters that are also found in the skeletons of aquatic reptiles other than choristoderes; most of the diagnostic features of choristoderes are skull features, but the presence of these cannot be confirmed in "Pachystropheus", as there is no confirmed skull material for this taxon. Silvio Renesto (2005) found similarities in the postcranial skeleton of "Pachystropheus" and the thalattosaur genus "Endennasaurus"; according to Renesto, these similarities may indicate that "Pachystropheus" and "Endennasaurus" are close relatives, but they might as well simply be a case of a convergent evolution triggered by the aquatic lifestyle of both taxa.