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Muraenosaurus
''Muraenosaurus'' (from the Latin "''Muraena''" meaning "eel" and "''Sauros''" meaning lizard) is an extinct genus of cryptoclidid plesiosaur reptile from the Oxford Clay of Southern England. The genus was given its name due to the eel-like appearance of the long neck and small head. ''Muraenosaurus'' grew to lengths between and and dates roughly to between 160 Ma (million years ago) and 164 Ma in the Callovian of the middle Jurassic. Charles E. Leeds collected the first ''Muraenosaurus'' which was then described by H. G. Seeley.〔Seeley, HG. 1874. On ''Murænosaurus Leedsii'', a Plesiosaurian from the Oxford Clay. Part I. ''Quarterly Journal of the Geological Society'' 30: 197-208.〕 The specimen may have suffered some damage due to the casual style of Charles Leeds’ collection. The first Muraenosaur was recovered with pieces missing from the skull and many of the caudal vertebrae absent. Because the animal was described from Charles Leeds’ collection it was given the name ''Muraenosaurus Leedsi''. ''M. leedsi'' is the most complete specimen belonging to the genus ''Muraenosaurus'' and also the only species that is undoubtedly a member of the genus. .〔 Two other species have been tentatively referred to as members of the genus ''Muraenosaurus'': ''M. reedii'' and ''Picrocleidus beloclis''〔Wilhelm BC. 2010. A New Partial Skeleton of a Cryptocleidoid Plesiosaur from the Upper Jurassic Sundance Formation of Wyoming. '' Journal of Vertebrate Paleontology '', ''30'', 6, 1736-1742.〕〔Muraenosaurus? Reedii, Sp. Nov. and Tricleidus? Laramiensis Knight, American Jurassic Plesiosaurs. ''The Journal of Geology'', ''20'', 4, 344-352.〕
''Muraenosaurus reedii'' was discovered in Wyoming and described by Maurice Mehl of the University of Chicago. The fossilized fragments found consisted of pieces of the pectoral and pelvic girdles, several vertebrae, ribs, and a relatively complete left pectoral paddle. Connections between ''M. leedsi'' and ''M. reedii'' were drawn when examining the ribs structure and paddle of ''M. reedii''. Both had a similarly shaped, elongated humerus and relatively short phalanges.〔 The species ''M. reedii'' is in fact a junior synonym of ''Pantosaurus''. ''Picrocleidus beloclis'' is another plesiosaur originating in the middle Jurassic and found in the Oxford clay formation. ''Picrocleidus'' has previously been considered synonymous with ''Muraenosaurus'' although there are doubts in the relationship between the two groupings.〔
==Description==
''Muraenosaurus'' was roughly 5 to 6 meters in length and owed roughly half of its body size to its long neck. The plesiosaur had 66 pre-sacral vertebrae; 44 of which were cervical. Starting from the base of the skull and moving posteriorly the cervical vertebrae elongate and the neural spines broaden. This may be indicative of increased muscle attachment towards the base of the neck.〔Richards, CD. 2011. ''Pleisiosaur body shape and its impact on hydrodynamic properties''. Huntington, WV: Marshal University Libraries〕 There is also a gradual flattening and reduction of the zygapohesis until about the 30th vertebra where all traces of the platform are gone. Posterior to the 44 cervical vertebrae, ''Muraenosaurus'' had 3 pectoral vertebrae and 19 thoracic vertebrae.〔〔 The pectoral vertebrae resemble the terminal cervical vertebrae but display a broadened face of the centrum and a slight posterior incline in the neural spines. In the dorsal vertebrae the rib has been raised onto the neural arch. The neural spines have elongated anteroposteriorly and compressed vertically.〔
The pectoral girdle in ''Muraenosaurus'' is broader than in most plesiosaurs and helped to situate the animal as a member of ''Cryptoclididae''. The coracoids reach widths of nearly 14 inches. The forelimb is compressed mediolaterally when compared to the hind limb as well as limbs of other plesiosaurs.〔〔O’Keefe FR. 2001. Ecomorphology of plesiosaur flipper geometry. ''Journal of Evolutionary Biology'', ''14'', 6, 987-991〕 This compression is represented in the aspect ratio of Muraenosaur limbs. The aspect ratio of the hind limbs is much greater than that of the fore limbs, representing a longer and more slender form.〔 The high aspect ratio in the forelimbs may have been used for increasing maneuverability at some cost to the animal’s endurance.
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