and at some Paleocene localities with fellow neochoristodere Simoedosaurus, though in assemblages where Champsosaurus occurs longirostrine (long snouted) gharial-like crocodilians are absent, suggesting that there was niche differentiation. Previously, two species of Champsosaurus were identified from the Tullock Formation in Montana. However, these differences are now thought to be sexually dimorphic, with presumed females possessing robust limb bones. Non-deformation related fusion of the sacral vertebrae is also observed in specimens with robust limb bones. These are hypothesised to be related to breeding behaviour, with the more robust limb bones and fused sacrals of the females allowing them to move themselves onto land to lay eggs. See also Tullock Formation Hell Creek Formation Paleontology in Montana References Paleontology in Alberta Fossils of Canada Choristodera Prehistoric marine reptiles Prehistoric reptile genera Maastrichtian genera Campanian genus first appearances Late Cretaceous reptiles of Europe Paleocene reptiles of Europe Late Cretaceous reptiles of North America Paleocene reptiles of North America Taxa named by Edward Drinker Cope Fossil taxa described in 1877