Boletín de la Sociedad Geológica Mexicana Volumen 69, núm. 1, 2017, p. 87 ‒ 134 http://dx.doi.org/10.18268/BSGM2017v69n1a6

A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico

Eberhard Frey^1,*, Eric W. A. Mulder², Wolfgang Stinnesbeck³, Héctor E. Rivera-Sylva⁴, José Manuel Padilla-Gutiérrez⁴, Arturo Homero González-González⁴

1 Staatliches Museum für Naturkunde Karl sruhe, Geowissenschaftliche Abteilung, Erbprinzenstraße 13, 76133 Karlsruhe, Germany.
2 Museum Natura Docet Wonderryck Twente, Oldenzaalsestraat 39, 7591 GL Denekamp, the Netherlands.
3 Universität Heidelberg, Institut für Geowissenschaften, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany.
4 Museo del Desierto, Carlos Abedrop Dávila 3745, Centro Metropolitano, Parque Las Maravillas, 25022 Saltillo, Mexico.
^* This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

A nearly complete skeleton of a polycotylid plesiosaur is described from the early Late Cretaceous laminated limestones at Vallecillo, northeast Mexico. It shows extensive soft tissue preservation. In some exceedingly well preserved areas there are transversely elongate rectangular to trapezoid millimetric scale-like structures arranged in longitudinal rows. The trailing edge skin flap preserves fibers and scale rows perpendicular to the trailing edge. A thick layer of subdermal tissue is present, especially along the tail base. It was responsible for the hydrodynamic drop-shaped body contour, with the body and tail forming a single unit. The body shape determined from the preserved soft tissues suggests a swimming speed similar to extant leatherback turtles. Based on the unique osteology of the palate, which is intermediate between Dolichorhynchops and Trinacromerum , and according to the unique morphology of the girdles and propodials as well as the medially converging gastralia, the new specimen is placed in a new genus and species of Polycotylidae, Mauriciosaurus fernandezi gen. et sp. nov.

Keywords: Vertebrate palaeontology, Plesiosauria, Polycotylidae, Late Cretaceous, northeast Mexico, soft tissue preservation, palaeoecology.