Champsosaurus annectens (Cope 1876) ~1.5 m in length, Late Cretaceous to Eocene. Champsosaurus was derived from a sister to the Doswellia and was a sister to other choristoderes, such as Cteniogenys and Lazarussuchus. This group must have originated in the Late Permian or Early Triassic, but fossils are chiefly from late survivors, hence the wide variety in their morphology.
Distinct from Cteniogenys and Doswellia, the skull of Champsosaurus had a longer rostrum and much larger temporal fenestrae. The maxillae met at the top of the rostrum isolating the anterior nasals, which are fused. The prefrontals fused with the posterior nasals. The temporal region was greatly expanded, likely to house large jaw muscles. Distinct from Doswellia, but not Cteniogenys, the posterior skull leaned posteriorly due to the expansion of the dorsal temporal fenestrae.
The cervicals and torso were low and wide, as in Doswellia. The dorsal ribs were thick. The tail was tall and narrow, idea for sculling (undulating while swimming).
The pectoral girdle was relatively small. The longest finger was digit 3.
The pelvis was likewise small with three sacral vertebrae. The hind limbs were longer than the forelimbs. Pedal digit 3 was the longest.