A DEEP-BODIED ICHTHYOSAUR (REPTILIA: ICHTHYOSAURIA) FROM THE UPPER JURASSIC KIMMERIDGE CLAY FORMATION OF DORSET, UK: IMPLICATIONS OF RIB CAGE ARCHITECTURE FOR ICHTHYOSAUR PALAEOECOLOGY

A new ichthyosaur specimen (MJML K1885) from the Late Jurassic (Kimmeridgian) Kimmeridge Clay Formation of Dorset, United Kingdom is described. The specimen, expertly prepared on a slab of laminated coccolith limestone, comprises a near complete skull, in articulation with the anterior vertebral column and associated thoracic ribs, complete pectoral girdle, fully exposed left forelimb, and some elements of the right forelimb.]

Aspects of the dentition, skull roof bones and the forelimb configuration distinguishes the new specimen from previously described Late Jurassic ichthyosaurs, and consequently it is referred to a new genus and species. A cladistics analysis reveals a close relationship with Nannopterygius with which the new taxon may form a distinct family as a sister clade to Ophthalmosauridae. A unique feature of MJML K1885 is its extremely deep anterior rib cage, suggesting perhaps a deep-diving habitat.

The new specimen adds to the diversity of Kimmeridge Clay Formation ichthyosaurs, and emphasises the important contribution of amateur collectors in palaeontology.