First Early Cretaceous ichthyosaurs of Austria and the problem of Jurassic–Cretaceous ichthyosaurian faunal turnover

Abstract

Here we report the first ichthyosaurian finds from the Valanginian and Hauterivian of Austria. Based on their tooth morphology, they represent two distinct taxa with probably different feeding ecologies. The Valanginian specimen is a small tooth with a small crown and bulbous root, similar to teeth of Nannopterygius and Sisteronia - it likely was a soft-prey specialist or generalist. Hauterivian specimen has markedly larger teeth with more robust crowns indicating that it most likely occupied an ecological niche of a generalist. Although these specimens are not possible to determine at genus and species level, they demonstrate that two ichthyosaurian taxa inhabited the seas covering what is nowadays Austria in the Valanginian and Hauterivian. The present-day data on stratigraphic distribution of ichthyosaurian taxa at the Jurassic-Cretaceous transitional interval do not support the presence of marked events in the ichthyosaurian evolutionary history during the Tithonian–Berriasian times. Globally, Hauterivian ichthyosaurian taxa are quite different from Tithonian–Berriasian taxa. Therefore, an appreciable event in the evolutionary history of ichthyosaurians likely took place during the Valanginian, which is still extremely poorly characterized by ichthyosaurian fossils, hampering the assessment of the exact timing and severity of this event.