| Sthenarosaurus | |
|---|---|
 | |
| Pectoral girdle ofSthenarosaurus .sp.[1] | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Plesiosauria |
| Family: | †Rhomaleosauridae |
| Genus: | †Sthenarosaurus Watson, 1909 |
| Species: | †S. dawkinsi |
| Binomial name | |
| †Sthenarosaurus dawkinsi Watson, 1909 | |
Sthenarosaurus (meaning "strong lizard") is anextinct genus ofrhomaleosauridpliosauroid discovered in theToarcian-aged 'Main Alum Shale' (Commune subzone ofBifrons zone)[2] inWhitby,England.[3] The type species,Sthenarosaurus dawkinsi, was named and described in 1909 byD. M. S. Watson.[4] The type specimen isMMUM LL 8023, a set of postcrania discovered in Whitby. Other indeterminate specimens are known,[3] including a pectoral girdle (pictured intaxobox) described in 1911.[1] Plesiosaurian fossils were acquired for theManchester Museum byWilliam Boyd Dawkins who is honoured by the specific name.
The holotype is known from an incomplete skeleton with no skull. A precise reconstruction is not possible, but it is assumed thatSthenarosaurus was a small plesiosaur, reaching up to 3 metres (9.8 ft) long when fully grown.[5] 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.[6]
Sthenarosaurus has been placed in the Pliosauroidea within Plesiosauria since it was described in 1909.[4] It was the sister taxon toArchaeonectrus (known at the time as "Plesiosaurus"rostratus), based on similarities in the shape of the shoulder blades, coracoids and cervical vertebrae.[4][1] Compared toArchaeonectrus however, the cervicals ofSthenarosaurus were longer. It is possible thatSthenarosaurus represents a currently unknown clade of plesiosaurs.[3]
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