New information on the skull roof ofProtoichthyosaurus(Reptilia: Ichthyosauria) and intraspecific variation in some dermal skull elements

Abstract

AbstractA previously unrecognized specimen ofProtoichthyosaurus prostaxalis, LEICT G142.1991, from the Lower Jurassic of Barrow-upon-Soar, Leicestershire, UK, includes an almost complete three-dimensional skull that provides new information on the configuration of the skull roof. The position of the pineal foramen (between the frontals and the parietals) and an elongated internasal foramen in a depression along the midline of the nasals are clearly shown. The maxilla makes up a significant portion of the external naris ventral margin, an unusual character for the genus/species. This reflects intraspecific variation, not evidence of a new taxon. The specimen enables comparisons of skull roof morphology withIchthyosaurusandStenopterygius, two common Early Jurassic taxa. In particular, the position of the pineal foramen is similar toStenopterygius, but distinguishesProtoichthyosaurusfromIchthyosaurus. The lack of a frontal–prefrontal contact and the posteriorly wide nasals distinguishesProtoichthyosaurusfromStenopterygius. We also present a revised reconstruction of the skull roof morphology ofIchthyosaurus. Three additional specimens ofProtoichthyosaurusare referred to the genus: another partial skull, referred toP. prostaxalis, and two isolated forefins, identified by their unique morphology.