A new large lamniform shark from the uppermost Gearle Siltstone (Cenomanian, Late Cretaceous) of Western Australia

An association of 100 teeth and 15 Vertebrae from a large, lamniform shark, is described from the uppermost part of the Gearle Siltstone in the Giralia Anticline, Southern Carnarvon Basin, Western Australia. The material represents a new genus and species: Casdabiodon ricki. The taxon is referred to the new family Cardabiodontidae on the basis of its dental formula and uniquely oversized lower lateroposterior teeth. Other characteristic features include a strong dignathic heterodonty and the presence of four anterior and approximately 14 lateroposterior tooth-files in both the upper and lower jaw. The size of the recovered Vertebral centra indicates that the shark measured at least 5 m in total length. The species had a wide but possibly patchy distribution with additional occurrences in England and Kazakstan, where it is present in strata of Cenomanian age. Cardabiodon shares several key dental characters with Parotodus, known from Oligocene-Pliocene deposits. The latter taxon was previously grouped with the 'mega-toothed' sharks of the genera Otodus and Carcharocles, but is here reassigned to the Cardabiodontidae. The nominal species Cretalamna woodwardi from the middle or late Cenomanian of southern England, is designated as the type species of the new genus Dwardius. The coeval nominal species Pseudoisurus tomosus from the Saratov region in Russia, is based on material that almost certainly includes C. ricki and/or D. woodwardi. Designation of a lectotype for P. tomosus and its proper documentation would probably allow either C. ricki or D. woodwardi to be synonomised with the older name P. tomosus. There is, however, a strong possibility that the syntypes of P. tomosus are lost. Until they are found, redescribed and compared carefully with the type material of C. ricki and D. woodwardi, P. tomosus is a name of doubtful application and therefore referred to as a nomen dubium.