Evidence for a second species of the ichthyosaur Platypterygius in North America: a new record from the Loon River Formation (Lower Cretaceous) of northwestern Canada

摘要

To date, all Cretaceous ichthyosaur material from North America has been referred to the species Platypterygius americanus. This species is generally identified based on skull and paddle morphology, but all non-diagnostic material from North America has been assigned to this species. A new Lower Cretaceous ichthyosaur from the Loon River Formation at Hay River, Northwest Territories, Canada, is described here. The specimen in question consists of the anterior portion of a large ichthyosaur, of which only the pectoral girdle is well preserved. It is assignable to Platypterygius, but is inconsistent with P. americanus based on paddle morphology. It shares most similarities with European and Australian species; unfortunately, it cannot be definitively assigned to any one taxon because of poor preservation of the skull. This specimen increases our knowledge of the diversity of North American Cretaceous ichthyosaurs, and suggests that the Cretaceous Western Interior Seaway was capable of sustaining a large taxonomic diversity of these marine reptiles, similar to the high numbers of Platypterygius species known from Europe.