A new leptonectid ichthyosaur from the Lower Jurassic (Hettangian) of Nottinghamshire, England, UK, and the taxonomic usefulness of the ichthyosaurian coracoid

摘要

Thousands of ichthyosaurs have been discovered from the rich Lower Jurassic deposits of the UK, with the majority collected from along the Lyme Regis-Charmouth area of the Dorset coast. Here, I describe a new leptonectid ichthyosaur, Wahlisaurus massarae gen. et sp. nov., based on a partial skull and an incomplete skeleton collected from the Lower Jurassic (Hettangian) of Nottinghamshire, England. Wahlisaurus can be referred to the Leptonectidae through the possession of an extremely slender and delicate snout, and a mandible shorter than the snout which produces an overbite. This referral is supported by a phylogenetic analysis. The new taxon is distinguished from other ichthyosaurs through a unique combination of characters and autapomorphies of the pectoral girdle including the presence of both a scapular-coracoid foramen and a large and roughly ovoid coracoid foramen. A coracoid foramen has only previously been reported in the Triassic ichthyosaur Cymbospondylus. The peculiar coracoid morphology further highlights the taxonomic utility of coracoids in ichthyosaurs. The aforementioned features demonstrate that W. massarae cannot be referred to any currently recognized leptonectid. Wahlisaurus is the ninth Lower Jurassic ichthyosaur genus to be recognized worldwide, and the fifth documented in the Lower Lias Group.