Catutosaurus gaspariniae , gen. et sp. nov. (Ichthyosauria, Thunnosauria) of the Upper Jurassic of Patagonia and the evolution of the ophthalmosaurids

FERNÁNDEZ, MARTA S.; CAMPOS, LISANDRO; MAXWELL, ERIN E.; GARRIDO, ALBERTO C.

JOURNAL OF VERTEBRATE PALEONTOLOGY

SOC VERTEBRATE PALEONTOLOGY

Año: 2021

0272-4634

ABSTRACT?Thunnosaurian ichthyosaurs were one of the most successful lineages of Mesozoic tetrapods in terms ofadaptation to a pelagic lifestyle. Among them, the ophthalmosaurids are of particular interest. Their fossils document anearly widespread distribution, including high northern and southern latitudes soon after they appear at the Aalenian?Bajocian boundary, becoming almost the only surviving lineage of ichthyosaurs for approximately 76 million years untiltheir extinction at the end of the Cenomanian (Late Cretaceous). Evolutionary innovations that could have been involvedin their remarkable evolutionary success are still poorly understood. Two regions of the skeleton, involved in two vitalfunctions ? breathing and swimming ? depict notable variation among ophthalmosaurids: the narial region and theproximal forefin configuration (i.e., stylopodium-zeugopodium-mesopodium pattern). Here, we describe Catutosaurusgaspariniae gen. et sp. nov., a new Tithonian (Late Jurassic) ophthalmosaurid from the northwest of Patagonia, Argentina.The new taxon depicts a peculiar pattern of the narial opening and forefin. Catutosaurus has an ?ophthalmosaurine-like?skull with reduced cheek, triangular squamosal, slender and delicate snout and rounded tooth roots; and ?platypterygiinelike?forefin composed by the typical polygonal and tightly packed elements and a broad articulation between thestylopodium and zeugopodial row. Phylogenetic analysis retrieves Catutosaurus nested within basal ophthalmosaurids, atthe base of a large clade named here as Panplatypterygiine. New information provided by Catutosaurus suggests thatchanges in the narial region and complexity of the stylopodium?zeugopodium articulation occurred independently amongophthalmosaurids and not in a stepwise manner along with the evolution of the clade.