Adriosaurus suessi (Seeley 1881) Late Cretaceous, ~95 mya, ~25 cm, wasn't a snake, but a close sister taxon. Derived from a sister to Ardeosaurus, Adriosaurus was a phylogenetic predecessor to the snake Pachyrhachis.
Distinct from Ardeosaurus, the skull of Adriosaurus was longer, as were the nares and nasals and premaxillary process. The postfrontal/postorbital contacted the prefrontal. The frontal and parietal were narrower. The sqauamosal was shorter. The teeth were longer. The coronoid process was taller.
The cervicals were smaller and more numerous as were the dorsals and caudals. The ribs were thicker (pachystotic). The dorsal ribs were shorter producing a more snake-like body.
The ilium was taller. The limbs were shorter. The metatarsals were subequal.