S imbirskiasaurus and P ervushovisaurus reassessed: implications for the taxonomy and cranial osteology of C retaceous platypterygiine ichthyosaurs

The ichthyosaur fossil record is interspersed by several hiatuses, notably during the C retaceous. This hampers our understanding of the evolution and extinction of this group of marine reptiles during the last 50 million years of its history. Several C retaceous ichthyosaur taxa named in the past have subsequently been dismissed and referred to the highly inclusive taxon P latypterygius , a trend that has created the impression of low C retaceous ichthyosaur diversity. Here, we describe the cranial osteology, reassess the stratigraphic age, and evaluate the taxonomy and phylogenetic relationships of two C retaceous ichthyosaurs from western R ussia: S imbirskiasaurus birjukovi from the early B arremian and P ervushovisaurus bannovkensis from the middle C enomanian, both formerly regarded as nomina dubia, and allocated to P latypterygius  sp. and P latypterygius campylodon , respectively. We show that S imbirskiasaurus birjukovi and P ervushovisaurus bannovkensis are valid platypterygiine ophthalmosaurids, notably characterized by a peculiar narial aperture. The cranial anatomy and phylogenetic relationships of these taxa illuminate the evolution of narial aperture anatomy in C retaceous ichthyosaurs, clarify the phylogenetic relationships among platypterygiines, and provide further arguments for a thorough revision of Platypterygius . © 2014 The Linnean Society of London