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

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

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. Described other species, ''S. dakotensis'' later got its own genus, ''

Kosmodraco ''Kosmodraco'' is a genus of large bodied choristodere from the Paleocene of North America. Originally described as a species of '' Simoedosaurus'', it was found to represent a distinct genus in 2022. Multiple fossil skulls show a relatively shor ...

''.

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 medicine ...

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 ''Tchoiria'' is a genus of simoedosaurid choristodere, a type of crocodile-like aquatic reptile. Fossils of this genus have been found in Early Cretaceous-age rocks in Mongolia. Four species have been named, but two have been given their own ...

'' and '' Ikechosaurus'' from the Early Cretaceous 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 younger 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 ''creta'', ...

of Asia makes this merely a paleogeographical speculation.

Biology

''Simoedosaurus'' was an aquatic predator, specialised to a fully aquatic lifestyle; though ''

Champsosaurus ''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 , () ...

'' 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 (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period (Cenomanian stage) and are the closest living ...

are present, including brevirostrine forms like ''

Borealosuchus ''Borealosuchus'' (meaning "boreal crocodile") is an extinct genus of crocodyliforms that lived from the Late Cretaceous to the Eocene in North America. It was named by Chris Brochu in 1997 for several species that had been assigned to '' Leidyo ...

''; 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 ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbeki ...

References

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