A small ichthyosaur from the Clearwater Formation (Alberta, Canada) and a discussion of the taxonomic utility of the pectoral girdle

摘要: Albian sedimentary successions of northwestern Canada have yielded a diverse assemblage Mesozoic marine vertebrates, and ichthyosaurs form an important component these faunas. Here, we describe partial postcranial skeleton small (estimated at less than 3 m total body length) ichthyosaur from the Wabiskaw Member Clearwater Formation (lowermost Albian). The semi-articulated specimen includes much presacral vertebral column, dorsal ribs gastralia. Most significantly, it possesses articulated pectoral girdle humerus, also preserves pelvic girdle, allowing new insights into evolution in ichthyosaurs. Whereas both sets girdles are thought to exhibit large amounts intraspecific variation, ophthalmosaurids appears evolve very slowly, remaining essentially unchanged Middle Jurassic onwards. In contrast, shows taxonomically informative changes within Ophthalmosauridae. variable poorly known nature morphology Cretaceous precludes generic referral specimen.