Plesiosaurus De la Beche and Conybeare, 1821
Classification
Sauropterygia > Eosauropterygia > Eusauropterygia > Pistosauroidea > Plesiosauria > Plesiosauroidea > Plesiosauridae
Synonyms - under construction
P. dolichodeirus Conybeare, 1824 (Type species)
Material
Type: BMNH 22656, complete skeleton.
Distribution
Uppermost Sinemurian, Lower Jurassic, Lyme Regis, Dorset, England.
Images
A. Pencil restoration of Plesiosaurus (original artwork by A. S. Smith). N.B. Although the illustration shows the alternating-flippers model of locomotion in plesiosaurs, the fore flippers are represented too high here (Martill pers. comm. 2002). B. Old title image for THE PLESIOSAUR DIRECTORY: a Plesiosaurus dolichodeirus skull (modified from Storrs, 1997).C and D . Type specimen of P. dolichodeirus (original specimen on display at the Natural History Museum, London. C - Photograph courtecy of Tom Challands, D, photo by Adam.S.Smith)
The skull of Plesiosaurus dolichodeirus as reconstructed by Storrs (1996). from left to right: dorsal, ventral, lateral views.
Model of Plesiosaurus by Hirokazu Tokugawa (used with kind permission of Hirokazu Tokugawa, see his other models at http://www2.neweb.ne.jp/wc/A-fragi)
'P'. brachypterygius von Huene, 1923
Species discussion
Fraas (1910) describes this taxon. Recently, Storrs (1997) modified Persson's (1963) suggestion that Plesiosaurus contains only three valid species by proposing P. brachypterygius as a junior synonym of P guilielmiiperatoris, reducing the number of valid Plesiosaurus species to two. Maisch and Rucklin (2000, p. 38) justified the retention of P. brachypterygius, but recent work by Grossman (2007) recognised this as a novel genus and named it Hydrorion brachypterygius.
Material
Type -GPIT 'GPIT von Huene'; complete skeleton including skull.
Distribution
Lias epsilon II, 4 (Unterer Schiefer), Harpoceras falcifer Zone, Lower Toarcian, Steinbruch 29, Ohmden (near Holzmaden), Baden-Württemberg.
Images
A. Photograph of the skeleton of a specimen labeled as P. brachypterygius (taken in the Uweltmuseum Hauff, Germany by A. S. Smith). B and C. Skeletons of P. brachypterygius (from Hauff, 1953)
3D restoration of P. brachypterygius by Adam Procházka. Photograph taken in the Uweltmuseum Hauff. Courtesy of S. M. Clabby.
P. guilielmiiperatoris
('Seeleysaurus' of White, 1940 and Grossman 2007)
Material: sorry, under construction
Images
Wonderful skeleton of P. guilielmiiperatoris with a close up of the skull (from Hauff, 1953)
Species discusion
Bakker (1993) retained the name Seeleysaurus for P. guilielmiiperatoris, a taxonomic change later justified and formalised by Grossman (2007).
Material: sorry, under construction
Species discussion
This species is quite distinct from other Plesiosaurus and deserves generic status of its own. It is currently under revision. An outdated description is given by Andrews (1896).
Images
A and B. Skull of 'P' macrocephalus ( referred specimen) in (A) dorsal view and (B) right lateral view (photograph of cast, taken in the Bristol Museum, by A. S. Smith). C and D. Skeleton of 'P' macrocephalus. C: Original specimen on display in the Natural History Museum, London (photograph courtecy of Tom Challands). D: (photograph of a (poor) cast in the collections of the Bath Institute, taken with permission by A. S. Smith)
Discussion
Plesiosaurus was the first plesiosaur to be discovered and was the first to be named. The genus Plesiosaurus is the sole member of the family Plesiosauridae. It is a rather poorly understood family, mostly because Plesiosaurus is a waste-basket taxon. This means that many different specimens have all been allocated to the genus Plesiosaurus, even when they were very different and probably deserve a name all of their own. This confusion was initiated during the 1800's when plesiosaurs were first being studied and described. Many of the species are now renamed and most of them do not even belong in the family Plesiosauridae. For example, 'Plesiosaurus' rostratus and 'Plesiosaurus' conybeari have been renamed Archaeonectrus and Attenborosaurus respectively; they are actually both pliosaurids. There are now no more than three valid species of Plesiosaurus (Storrs, 1997) although some remain e.g. 'Plesiosaurus' macrocephalus pending revision. The valid species (dolichodeirus, guilielmiiperatoris and brachypterygius) comprise the family Plesiosauridae (for now at least...).
