A new postcranial skeleton of an elasmosaurid plesiosaur from the Upper Cretaceous of central Chile and reassessment of Cimoliasaurus andium Deecke

We describe a new specimen of an elasmosaurid plesiosaur from the upper Maastrichtian of central Chile. The specimen includes a relatively complete dorso-caudal series, a few cervical vertebrae, and a fragmentary pelvic girdle. The specimen is identified as a sub-adult non-artistonectine elasmosaurid (Sauropterygia, Plesiosauria) based on graphic bivariate analysis of the cervical vertebral proportions. The caudal vertebrae have distinctive features such as neural arches that are recurved cranially, with pedicels overlapping the dorso-posterior surface of the immediately anterior centrum, and terminal centra with two pairs of deep dorsal articulations for the neural arches. These unusual features are present in several late Maastrichtian adult specimens from the Quiriquina Formation of central Chile, and have been included within the hypodigm of the historic taxon Cimoliasaurus andium Deecke (nomen dubium). The specimen studied here likely represents the same taxon or a closely related form, showing slight differences in both size and ontogenetic stage. The preserved elements of this new skeleton afford comparison with several other late Maastrichtian specimens from Chile that were previously, albeit tentatively, referred to “C. andium”. The similarity of these specimens suggests that the late Maastrichtian elasmosaurid diversity of central Chile (excluding aristonectines) may be represented by taxa with low morphological disparity, or by a single taxon.