Current Taxonomic Status of the Plesiosaur Pantasaurus Striatus from the Upper Jurassic Sundance Formation, Wyoming

摘要

Plesiosaur material has been known from the Redwater Shale member of the Sundance Formation (Jurassic: Oxfordian) of Wyoming for over 100 years, but has received little research attention. Here we report on the taxonomic status of a long-necked cryptocleidoid plesiosaur from the Redwater Shale, the correct identity of which is Pantosaurus striatus Marsh 1893. The taxon Muraenosaurus reedii Mehl 1912 is shown to be a junior synonym of Pantosaurus striatus. Pantosaurus is described on the basis of the holotype and referred specimens, and found to be a cryptocleidoid plesiosaur possessing between 35 and 40 cervical vertebrae. These vertebrae are very similar in proportion and anatomical detail to those of Muraenosaurus leedsii from the Oxford Clay of England. However, the forelimb of Pantosaurus is diagnostic and differs from that of Muraenosaurus in several particulars, the most important being the relatively large size of the radius and its corresponding humeral articulation. Although no cranial material is available at this time, we believe that Pantosaurus striatus is a valid taxon.