Simoedosaurus is an extinct reptile known from the Paleocene of North America, Europe and western Asia,[1] and a member of the Choristodera, a group of aquatic reptiles that lived in the Northern Hemisphere from the Jurassic to the early Cenozoic.

[4] It in particular possesses broader, stronger jaws than other longirostrine choristoderes, including its closest relatives, suggesting that it was capable of tackling larger prey.

[5] Simoedosaurus does occur in sites where aquatic crocodilians are present, including brevirostrine forms like Borealosuchus; the extent of competition between both groups, if there was any, is still unresolved.

[6] Like other neo-choristoderes it has nasal conchae, suggesting it could regulate its own body temperature, explaining its ability to live in cold waters.

[7] The earliest records of Simoedosaurus are from the Early Paleocene (Puercan Land Mammal Age) of Saskatchewan.