The Champsosaur was a freshwater, crocodile-like diapsid reptile that lived in North America and Europe 60 to 55 million years ago, from the Upper Cretaceous, through the Paleocene, finally becoming extinct only at the end of the Eocene.
Champsosaur fossils are found mostly in carbonaceous claystones and mudstones, indicating that their habitats were mostly sub-tropical lakes, ponds, and swamps.Champsosaurus belong to the order Choristodera, and with their long, narrow snouts, resemble India’s modern day Gharial. However, Champosaurs were not actually crocodilians, with their resemblance as a classic case of convergent evolution in a similar ecological niche. Judging from modern gharials however, Champsosaurs are likely to also have be nimble: Gharials are the quickest crocodilians in the world, reaching swimming speeds of 40 km/h while pursuing fish.
Unlike the dinosaurs that perished in the Cretaceous extinction event, the Champsosaur – together with aquatic reptiles such as turtles and crocodilians – persisted into the Paleocene probably by finding protection in the water.
Champosaurs were typically about 1.5m long, although the largest Champosaurus species was the Champsosaurus gigas, which grew to 3.5m. Reptiles generally decreased in size after the K-T event, and C. gigas was interesting because it instead became larger than its ancestors. C. gigas are found in North Dakota’s Paleocene stratum, including Sentinel; Butte; Bullion; Creek; Slope; Cannonball; and Ludlow.
The Champsosaur probably swam with lateral body movements, pinning its limbs against its body to increase its streamline, just like crocodiles. Its tail was also laterally compressed to aid in swimming. Powerful jaw muscles were attached to the wide skull space behind the Champsosaur eyes. Because of its hydrodynamic body, powerful back legs, and long snout studded with small, sharp, needle-like teeth, it is believed that the Champsosaurus was an aggressive underwater predator that would lie on the bottom of ponds waiting for prey. As a fish swam by, it was believed to spring off the bottom with its powerful back legs to attack the fish. Fish species found with Champsosaur bones include bowfin, gar, and pike.
This original underground find, measuring about 14 inches long, was found in one piece with no restoration done. It was legally collected on private deeded land in Powder River County, Montana with the land owner’s permission. Looking closely, we can identify the cervical neck, dorsal back, sacrum, and caudal tail. Collectors can identify Champosaur vertebrae by their hourglass shape, in contrast for instance with crocodile vertebrae which feature convex ends.