Cranial anatomy of a new plesiosaur genus from the lowermost Lias (Rhaetian/Hettangian) of Street, Somerset, England

Abstract

ABSTRACT A newly prepared plesiosaur skull collected by Thomas Hawkins (1810–1889) from the Lias quarries of Street, Somerset, England, provides important indications of character polarity within the Plesiosauria. Many features of the 3-dimensional, matrix-free skull are seemingly plesiomorphic in accord with the early, probably latest Rhaetian, stratigraphic position of the specimen. The small supratemporal fenestrae, elongate jugals, deeply excavated cheek, spatulate mandibular symphysis, and other characters thus have important implications for phylogenetic studies of the Plesiosauria. A new genus is erected to include the skull and several other specimens of historical importance that comprise part of the oldest known fauna of fully articulated plesiosaurs.