''Seldsienean'' (

Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlement of Britain, Anglo ...

for "seldom seen one") in an extinct genus of machimosaurid thalattosuchian from the

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

of England and France. It is known from the Calcaire de Caen and the

Cornbrash Formation The Cornbrash Formation is a Middle Jurassic geological formation in England. It ranges in age from Bathonian to Callovian, the uppermost part of the Middle Jurassic. Dinosaur remains are among the fossils that have been recovered from the forma ...

. Its

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

, ''S. megistorhynchus'', was originally described as a species of '' Steneosaurus'' in 1866, but was given its own genus in 2020.

References

Thalattosuchians Fossil taxa described in 2020 Prehistoric pseudosuchian genera {{Paleo-archosaur-stub