Catutosaurus gaspariniae, gen. et sp. nov. (Ichthyosauria, Thunnosauria) of the Late Jurassic of Patagonia and the Evolution of the Ophthalmosaurids

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

JOURNAL OF VERTEBRATE PALEONTOLOGY

SOC VERTEBRATE PALEONTOLOGY

Lugar: Lawrence; Año: 2021

0272-4634

Thunnosaurian ichthyosaurs were one of the most successful lineages of Mesozoictetrapods in terms of adaptation to a pelagic lifestyle. Among them, the ophthalmosaurids are ofparticular interest. Their fossils document an early widespread distribution, including high northernand southern latitudes soon after they appear at the Aalenian?Bajocian boundary, becomingalmost the only surviving lineage of ichthyosaurs for approximately 76 million years until theirextinction at the end of the Cenomanian (Late Cretaceous). Evolutionary innovations that couldhave been involved in their remarkable evolutionary success are still poorly understood. Tworegions of the skeleton, involved in two vital functions? breathing and swimming? depict a notablevariation among ophthalmosaurids: the narial region and the proximal forefin configuration (i.e.stylopodium?zeugopodium?mesopodium pattern). Here, we describe Catutosaurus gaspariniaegen. 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. Catutosaurushas an ?ophthalmosaurine-like? skull with reduced cheek, triangular squamosal, slender and delicatesnout and rounded tooth roots; and ?platypterygiine-like? forefin composed by the typical polygonaland tightly packed elements and a broad articulation between the stylopodium and zeugopodialrow. Phylogenetic analysis retrieves Catutosaurus nested within basal ophthalmosaurids, at thebase of a large clade named here as Panplatypterygiine. New information provided byCatutosaurus suggests that changes in the narial region and complexity of the stylopodium?zeugopodium articulation occurred independently among ophthalmosaurids and not in a stepwisemanner along with the evolution of the clade.