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

作者：Maxwell Erin E^*; Druckenmiller Patrick S

来源：Palaeontologische Zeitschrift, 2011, 85(4): 457-463.

DOI：10.1007/s12542-011-0106-0

• Ichthyosauria
• Ophthalmosauridae
• Lower Cretaceous
• Clearwater Formation
• Canada

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

• 出版日期2011-12