''Sthenarosaurus'' (meaning "strong lizard") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of

rhomaleosaurid Rhomaleosauridae is a family of plesiosaurs from the Earliest Jurassic to the latest Middle Jurassic ( Hettangian to Callovian stages) of Europe, North America, South America and possibly Asia. Most rhomaleosaurids are known from England, man ...

pliosauroid Pliosauroidea is an extinct clade of plesiosaurs, known from the earliest Jurassic to early Late Cretaceous. They are best known for the subclade Thalassophonea, which contained crocodile-like short-necked forms with large heads and massive tooth ...

discovered in the

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarcian ...

-aged ' Main Alum Shale' (Commune subzone of

Bifrons In ancient Roman religion and myth, Janus ( ; la, Ianvs ) is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. He is usually depicted as having two faces. The month of January is named for Janu ...

zone)Sepkoski, Jac
Sepkoski's Online Genus Database – Cephalopoda
/ref> in

Whitby Whitby is a seaside town, port and civil parish in the Scarborough borough of North Yorkshire, England. Situated on the east coast of Yorkshire at the mouth of the River Esk, Whitby has a maritime, mineral and tourist heritage. Its East Clif ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. The type species, ''S. dawkinsi'', was named and described in 1909.D. M. S. Watson. 1909. IV. A preliminary note on two new genera of upper Liassic plesiosaurs. ''Memoirs and Proceedings of the Manchester Literary and Philosophical Society'' 54(4):1-28 The type specimen is MMUM LL 8023, a set of postcrania discovered in Whitby. Other indeterminate specimens are known, including a pectoral girdle (pictured in taxobox) described in 1911.

Description

The holotype is known from an incomplete skeleton with no skull. A precise reconstruction is not possible, but it is assumed that ''Sthenarosaurus'' was a small plesiosaur, reaching up to long when fully grown. The coracoids were short and thick, while the pelvis was broad and strong. The dorsal vertebrae possessed short, but very broad and high vertebral centers, with thick neural spines. Eighteen cervical vertebrae are preserved, and vary greatly in size: the largest is almost double the smallest; this suggests that if the entire neck had been made up of even a few more vertebrae than those preserved, the animal would have had a strange appearance, due to noticeable thinning of the neck in the head area.T. E White. 1940. Holotype of ''

Plesiosaurus longirostris ''Hauffiosaurus'' is an extinct genus of Early Jurassic (early Toarcian stage) pliosaurid plesiosaur known from Holzmaden of Germany and from Yorkshire of the United Kingdom. It was first named by Frank Robin O’Keefe in 2001 and the type specie ...

'' (Blake) and classification of the plesiosaurs. ''Journal of Paleontology'' 14 (5): 451-467

Classification

''Sthenarosaurus'' has been placed in the Pliosauroidea within Plesiosauria since it was described in 1909. It was the sister taxon to ''

Archaeonectrus ''Archaeonectrus'' is an extinct genus of pliosaur from the Early Jurassic (Sinemurian) of what is now southeastern England. The type species is ''Archaeonectrus'' (originally ''"Plesiosaurus"'') ''rostratus'', first named by Sir Richard Owen in ...

'' (known at the time as "''

Plesiosaurus ''Plesiosaurus'' (Greek: ' ('), near to + ' ('), lizard) is a genus of extinct, large marine sauropterygian reptile that lived during the Early Jurassic. It is known by nearly complete skeletons from the Lias Group, Lias of England. It is disting ...

''" '' rostratus''), based on similarities in the shape of the shoulder blades, coracoids and cervical vertebrae. Compared to ''Archaeonectrus'' however, the cervicals of ''Sthenarosaurus'' were longer. It is possible that ''Sthenarosaurus'' represents a currently unknown clade of plesiosaurs.

References

Early Jurassic plesiosaurs of Europe Fossils of Great Britain Sauropterygian genera {{plesiosaur-stub

Description

Classification

See also

References