''Simoedosaurus'' is an extinct reptile known from the

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

of North America, Europe and western Asia, and a member of the Choristodera, a group of aquatic reptiles that lived in the Northern Hemisphere from the Jurassic to the early Cenozoic. A second species, ''S. dakotensis'' got its own genus, '' Kosmodraco'', in 2022.

Taxonomy

French paleontologist

Paul Gervais Paul Gervais (full name: François Louis Paul Gervais) (26 September 1816 – 10 February 1879) was a French palaeontologist and entomologist. Biography Gervais was born in Paris, where he obtained the diplomas of doctor of science and of medic ...

described ''Simoedosaurus'' in 1877. Though similar to and contemporaneous, ''Simoedosaurus'' is not closely related to the North American ''Champsosaurus'', instead it appears to be most closely related to '' Tchoiria'' and '' Ikechosaurus'' from the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

of Asia. It therefore may represent a species that immigrated into North America from Asia in the wake of the Cretaceous-Tertiary mass extinction event, though the absence of choristoderes in the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

of Asia makes this merely a paleogeographical speculation.

Biology

''Simoedosaurus'' was an aquatic predator, specialised to a fully aquatic lifestyle; though '' Champsosaurus'' might have still come ashore to lay eggs, ovovivipary is known in other choristoderes. It in particular possesses broader, stronger jaws than other longirostrine choristoderes, including its closest relatives, suggesting that it was capable of tackling larger prey. ''Simoedosaurus'' does occur in sites where aquatic

crocodilians Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchi ...

are present, including brevirostrine forms like '' Borealosuchus''; the extent of competition between both groups, if there was any, is still unresolved. Like other neo-choristoderes it has nasal conchae, suggesting it could regulate its own body temperature, explaining its ability to live in cold waters.

Range

The earliest records of ''Simoedosaurus'' are from the Early Paleocene (Puercan Land Mammal Age) of Saskatchewan. It persisted until the Late Palaecene in North America, and has also been found in the Late Paleocene of France. The youngest remains seem to occur in the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a landlocked country primarily in Central Asia, with a European Kazakhstan, small portion in Eastern Europe. It borders Russia to the Kazakhstan–Russia border, north and west, China to th ...

References

{{Taxonbar, from=Q2164813 Choristodera Paleocene reptiles Eocene reptiles Extinct animals of Europe Extinct animals of North America Prehistoric marine reptiles Prehistoric reptile genera