''Seldsienean'' (

Old English Old English ( or , or ), 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 developed from the languages brought to Great Britain by Anglo-S ...

for "seldom seen one") is an extinct genus of machimosaurid

thalattosuchia Thalattosuchia is a clade of mostly marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are colloquially referred to as marine crocodiles or sea crocodiles, though they are not member ...

n from the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

of England and France. It is known from the

Calcaire de Caen The Calcaire de Caen or Calcaires de Caen Formation; French language, French for Caen Limestone, is a geological Formation (geology), formation in France. It dates back to the mid-Bathonian of the Jurassic period.Weishampel, David B; et al. (2004) ...

and the Cornbrash Formation. Its

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

, ''S. megistorhynchus'', was originally described as a species of ''

Steneosaurus ''Steneosaurus'' (from , 'narrow' and , 'lizard') is a dubious genus of teleosaurid crocodyliform from the Middle or Late Jurassic (Callovian or early Oxfordian) of France. The genus has been used as a wastebasket taxon for thalattosuchian ...

'' in 1866, but was given its own genus in 2020.

References

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