A new Lower Cretaceous ichthyosaur from Russia reveals skull shape conservatism within Ophthalmosaurinae

Abstract

AbstractOphthalmosaurinae is a recently recognized clade of derived ichthyosaurs (marine reptiles) ranging from the Bajocian (Middle Jurassic) to the late Albian (late Early Cretaceous). Whereas the Middle–Late Jurassic ophthalmosaurineOphthalmosaurusis often regarded as a hyperspecialized deep diver, very little is known about the anatomy, evolutionary history and ecology of Cretaceous ophthalmosaurines because of the scarcity of the fossils and the lack of well-preserved skull material. Here, we describe the skull of a new basal ophthalmosaurine ichthyosaur,Leninia stellansgen. et sp. nov., from the lower Aptian of western Russia, and compare the ocular characteristics of ophthalmosaurids.Leniniais recovered as a basal ophthalmosaurine; it possesses unique traits such as a star-shaped frontal–parietal suture as well as features previously thought to be unique toOphthalmosaurussuch as a supratemporal–stapes contact. A large sclerotic aperture – significantly larger than in platypterygiine ophthalmosaurids and similar to that of the largest-eyed modern animals (giant and colossal squids) – and reduced dentition appear widespread within ophthalmosaurines. This conservatism suggests ophthalmosaurine ophthalmosaurids occupied similar ecological niche(s) throughout their long evolutionary history.