A second primitive marine snake: Pachyophis woodwardi from the Cretaceous of Bosnia-Herzegovina

The fossil of a second primitive snake from Cretaceous marine sediments is identified and redescribed: Pachyophis woodwardi Nopcsa. This snake was sim ilar to Pachyrhachis in having pachyostotic vertebrae, a slender neck and a small head. However, Pachyophis differed from Pachyrhachis in being even m ore aquatically adapted: the mid-dorsal vertebrae and ribs are more swollen (pachyostotic), the body was more laterally compressed, and the dentary co ntains more teeth. The hindlimb (well developed in Pachyrhachis) cannot be confirmed as present or absent in Pachyophis. A cladistic analysis demonstr ates that Pachyophis and Pachyrhachis form a clade. This grouping, here ter med the Pachyophiidae, forms the most basal group of snakes so far known an d is the sister group to all other well-known snakes.