Champsosaurus is an extinct genus of crocodile-like choristodere reptile, known from the Late Cretaceous and early Paleogene periods of North America and Europe (Campanian-Paleocene). The name Champsosaurus is thought to come from , () said in an Ancient Greek source to be an Egyptian word for "crocodiles", and , () Greek for "lizard". The morphology of Champsosaurus resembles that of gharials, with a long, elongated snout. It was native to freshwater environments where it likely preyed on fish, similar to living gharials. History of research Champsosaurus was the first member of the Choristodera to be described. Champsosaurus was named by Edward Drinker Cope in 1876, from isolated vertebrae found in Late Cretaceous strata of the Judith River Formation on the banks of the Judith River in Fergus County, Montana. Cope designated C. annectens as the type species rather than the first named C. profundus due to the larger number of vertebrae he attributed to the species. C. annectens was based on 9 isolated vertebral centra (AMNH FR 5696) that were not figured in the paper of which two are now lost. Cope named several other species between 1876 and 1882, also based on isolated vertebrae. Barnum Brown in 1905 described the first complete remains of Champsosaurus, and noted that one of the species attributed to Champsosaurus by Cope in 1876, C. vaccinsulensis actually represented indeterminate plesiosaur remains, and that the vertebrae that Cope used to diagnose his species of Champsosaurus were heavily eroded and the diagnostic features varied substantially along the spinal column, and were not diagnostic to species level, including the remains that Cope attributed to the type species C. annectens. The conclusion that C. annectens was undiagnostic was supported by William Parks in 1933. Brown in 1905 named two species of Champsosaurus. One was C. ambulator, named from the specimen AMNH 983, a fragmentary skeleton with a partial skull found in the Hell Creek Formation of Montana. The other was C. laramiensis, named from AMNH 982, a nearly complete skeleton and skull, also found in the Hell Creek Formation. Parks in 1927 named C. albertensis from ROM 806, a partial skeleton lacking the skull, found in the Horseshoe Canyon Formation in Alberta, Canada. Parks in 1933 named the species C. natator from an incomplete skeleton with a fragmentary skull (TMP 81.47.1) found in the Belly River Group in the Red Deer River valley in Alberta. In 1979, Denise