A new elasmosaurid (Sauropterygia, Plesiosauria) from the upper levels of the La Colonia Formation (upper Maastrichtian), Chubut Province, Argentina

Abstract

A new elasmosaurid, Chubutinectes carmeloi gen. et sp. nov., from the Chubut Province, Argentina, is described. The holotype and only specimen of this species (MPEF-PV 5232) was collected from the La Colonia Formation. Chubutinectes carmeloi gen. et sp. nov. is among the few upper Maastrichtian elasmosaurids from the Southern Hemisphere whose postcranial anatomy is well known. It can be distinguished from other elasmosaurids by the following combination of characters: middle cervical centra longer than high with lateral keel and bilobate articular faces; pectoral and anterior dorsal centra with bilobate articular faces; coracoids with closed cordiform fenestra and long anterior coracoids process; high ratio coracoids/scapular length; ilium with angled shaft; pubis with small lateral cornua; humerus with posterior expansion ending in accessory facet and epipodial facets of humerus almost aligned; accessory ossification between tibia and tibial, and radius and radial. Preliminary phylogenetic analysis recovered Chubutinectes carmeloi gen. et sp. nov. within the Weddellonectia clade, including the Late Cretaceous Wedellian aristonectine elasmosaurids. The study of the associated microfossiliferous assemblages (micro- and nanofossils) suggests a marine inner neritic paleoenvironment, with restricted circulation and warm waters. The presence of Micula prinsii and Micula murus at this latitude indicates a latest Maastrichtian age, upper part of the UC20d sub-biozone and younger than ∼67,3 Ma.