Late Jurassic ichthyosaurs from the Neuquén Basin (Central-West Argentina): new insights into the phylogeny of the Ophthalmosauridae

FERNÁNDEZ, MARTA S.; CAMPOS, LISANDRO; MAXWELL, ERIN; HERRERA, YANINA

Congreso; 5th International Palaeontological Congres; 2018

Ophthalmosaurids were advanced ichthyosauromorphs. Their evolution, from the Aalenian to theCenomanian, encompassed half of the history of the whole clade. The traditional conception ofophthalmosaurids as the last representatives of a declining lineage has radically changed in the last decades. New discoveries and studies indicate that ophthalmosaurids dominated soon after they emerged, probably at the Aalenian-Bajocian boundary, and achieved a widespread geographical distribution. Although their oldest records were recovered from the Neuquén Basin (Argentina) most of their fossils have been collected from the northern hemisphere. Southern hemisphere records are mainly restricted to Australia, Argentina and Chile, and to isolated material from Madagascar. Four nominal ophthalmosaurid taxa are recognized from the southern margins of the eastern paleopacific: Mollesaurus periallus, Caypullisaurus bonapartei, ?Platypterygius? hauthali and Arthropterygius sp. We assigned a new name for the reception of an ophthalmosaurid of Patagonia and included it in an expanded version of datasets to explore its phylogenetic affinities. The new taxon depicts a peculiar pattern of an ?ophthalmosaurine-like? skull and a platypterygine-like? forefin. Cladistic analysis recovered it forming a polytomy at the base of the platypterygine clade, and the ?ophthalmosaurines? are found as a paraphyletic assemblage. All boreal forms are nested within platypterygines but only three of them (Cryopterygius, Janusaurus and Arthropterygius) form a subclade. Stratigraphic calibration of the tree indicates that the platypterygiine radiation occurred earlier than previously supposed, probably during the late Middle Jurassic.