Shastasaurid ichthyosaurs and other lost critters from the French Rhaetian

Recent advances in the phylogeny and evolution of diversity of ichthyosaurs have recognized a smaller number of more intense turnovers compared to the previous understanding of their evolutionary history. One of these crucial turnovers occurred during the Late Triassic, when all ichthyosaur clades but a minor subset, the parvipelvians, went extinct. The timing and, hence, the severity of this event is however poorly understood and may have been protracted over the entire middle Norian–latest Rhaetian interval, more than 15 million years. The iconic, whale-sized shastasaurid ichthyosaurs are regarded as early victims of this turnover, disappearing by the middle Norian. In 1883, Henry Emile Sauvage (1842–1917), a famous French palaeontologist, described reptilian remains from a Rhaetian bonebed near Autun in eastern France. But this material was subsequently lost and disappeared from the literature. We have re-discovered most of this material in the fossil vertebrates collections of the Katholieke Universteit Leuven, Belgium. Reassessment of this material indicates the presence of very large shastasaurid ichthyosaurs (Ichthyosaurus rheticus, Rachitrema pellati [partim]), probable choristoderes (Actiosaurus gaudryi) and plesiosaurs (Plesiosaurus bibractensis). The occurrence of shastasaurids in Rhaetian strata is corroborated by recent findings in a new locality in southern France. This suggests that the final extinction of this important Triassic clade coincides with the rapid radiation of neoichthyosaurs, forming a short but extremely profound turnover that drastically impacted the evolutionary history of ichthyosaurs.