Abstract

This paper offers a preliminary description of a plesiosaur (Reptilia: Sauropterygia) from the Lower Toarcian Posidonienschiefer near the village of Holzmaden in Baden-Württemberg, Germany, and discusses its phylogenetic relevance. This new taxon, Plesiopterys wildi new genus and species, is remarkable in its retention of several plesiomorphic features. A phylogenetic analysis places Plesiopterys as the sister group of the Plesiosauroidea, and as such the taxon is the most basal taxon yet known on the branch leading to this major clade. Plesiopterys possesses a high count of cervical vertebrae and a relatively small head, yet the limbs and limb girdles are plesiomorphic in proportion. The skull displays a mosaic of features, reminiscent of both Thalassiodracon and the rhomaleosaurids in some characters, yet similar to Plesiosaurus in others. The basicranium is plesiomorphic and resembles that of nothosaur-grade sauropterygians in several respects. A faunal comparison between Holzmaden and the Lower Toarcian deposits on the Yorkshire coast of England concludes that the Holzmaden fauna is more plesiomorphic than the roughly coeval Yorkshire fauna in two of three plesiosaur subclades.

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