Eternauta patagonica gen. et sp. nov.: A new ophthalmosaurid ichthyosaur from the Upper Jurassic of Patagonia and its palaeoecological implications

Ophthalmosaurids were a globally distributed clade of ichthyosaurs that thrived from the Middle Jurassic to the early Late Cretaceous. Although their fossil record spans a wide palaeogeographic range, much of what is known about their anatomy and diversity derives from Late Jurassic localities in the Northern Hemisphere. In contrast, Late Jurassic forms from the Southern Hemisphere remain comparatively less known. Here we describe Eternauta patagonica gen. et sp. nov. a new ophthalmosaurid from the Tithonian deposits of the Vaca Muerta Formation. The holotype, previously referred to Caypullisaurus bonapartei Fernández, 1997, comprises a skull, teeth, a forelimb, and rib fragments. Phylogenetic analyses consistently recover Eternauta as a member of Platypterygiinae. Diagnostic features include a unique morphology of the pterygoid, an expanded postorbital contribution to the ventral margin of the orbit, and a retroarticular process that is strongly angled posterodorsally. These traits, together with a low jaw-opening mechanical advantage and relatively large sclerotic aperture, suggest a feeding strategy for capturing small, agile prey. The anatomical and functional features of Eternauta expand the known morphological and ecological disparity of Late Jurassic ophthalmosaurids, reinforcing the significance of the Vaca Muerta Formation as a key unit for understanding ichthyosaur evolution across the Jurassic – Cretaceous transition.