Unusual plesiosaur vertebrae from the Lower Jurassic Posidonia Shale of Germany

Abstract

ABSTRACT The Toarcian (upper Lower Jurassic) strata of the world-renowned Posidonia Shale of Central Europe have yielded diverse assemblages of marine vertebrates. Some of them, such as those of the Holzmaden area in southwestern Germany, are among the best-preserved specimens of Lower Jurassic vertebrate taxa. Here, we provide a reassessment of ‘Plesiosaurus’ bavaricus, a long-overlooked plesiosaur taxon from the Posidonia Shale of northern Bavaria (southern Germany), established based upon two isolated cervical centra and a caudal vertebra. The cervical material exhibits an intriguing character combination, providing evidence for the presence of a distinct plesiosaur taxon in the upper Lower Jurassic of the Posidonia Shale of Germany. Additionally, we report another isolated cervical vertebra, likewise from the Posidonia Shale of Bavaria, that shows striking similarities to the type cervicals of ‘P’. bavaricus. Following our study of the Bavarian specimens, we hypothesise that, despite their substantial incompleteness, it seems likely that the material belonged to the same taxon, either species or a group of species, distinct from other plesiosaurs known from the Posidonia Shale.