THE CRANIAL OSTEOLOGY OF THE ICHTHYOSAURLEPTONECTESCF. TENUIROSTRISFROM THE LOWER JURASSIC OF ENGLAND

For the first time, a three-dimensionally preserved skull of the Lower Jurassic leptonectid ichthyosaur Leptonectes cf. tenuirostris is described. The specimen reveals a wealth of new data on the cranial anatomy of basal leptonectid neoichthyosaurs. The osteology of the skull roof differs fundamentally from other well-known post- Triassic ichthyosaurs and is highly autapomorphic. The structure of the sclerotic ring, which is well preserved in situ, is described and it appears plausible that L. cf. tenuirostris was capable of stereoscopic vision. Inadequate description makes comparison to other leptonectids difficult. It can be demonstrated, however, that L. cf. tenuirostris is most similar to L. tenuirostris among known leptonectids. It is fundamentally different from the Upper Liassic Eurhinosaurus longirostrisin the osteology of the skull roof and the size and orientation of the major skull openings, making generic distinction of these two species a necessity. At the moment, no autapomorphies are known of the genus Leptonectes, which therefore must be considered as a metataxon that comprises basal leptonectids from the Lower to Middle Liassic.