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

• Published in: Geological magazine Vol. 151; no. 1; pp. 60 - 70
• Main Authors: FISCHER, VALENTIN, ARKHANGELSKY, MAXIM S., USPENSKY, GLEB N., STENSHIN, ILYA M., GODEFROIT, PASCAL
• Format: Journal Article Web Resource
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.01.2014
• Subjects: anatomy; Anatomy & physiology; Aptian; bones; Chordata; Commonwealth of Independent States; Cretaceous; Diapsida; Earth sciences & physical geography; Ecology; Europe; faunal studies; Fossils; Geological time; Head; Ichthyosauria; Jurassic; Kriushi Russian Federation; Leninia; Leninia stellans; Life sciences; Lower Cretaceous; Mesozoic; morphology; Ophthalmosaurinae; Original Articles; paleoecology; Paleontology; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Reptiles; Reptiles & amphibians; Reptilia; Russian Federation; Sciences de la terre & géographie physique; Sciences du vivant; skull; Tetrapoda; Ulyanovsk; Ulyanovsk Russian Federation; Vertebrata; vertebrate; Vision; Volga River valley; Zoologie; Zoology; vision; ecology; Ophthalmosauridae; Aptian; Ulyanovsk
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756812000994

Ophthalmosaurinae 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 ophthalmosaurine Ophthalmosaurus is 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 stellans gen. et sp. nov., from the lower Aptian of western Russia, and compare the ocular characteristics of ophthalmosaurids. Leninia is 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 to Ophthalmosaurus such 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.