Aristonectes quiriquinensis, sp. nov., a new highly derived elasmosaurid from the upper Maastrichtian of central Chile

ABSTRACT

This paper describes a new species of elasmosaurid plesiosaur, Aristonectes quiriquinensis, sp. nov., based on a partial skeleton recovered from upper Maastrichtian beds of the Quiriquina Formation of central Chile. The material described here consists of two skeletons, one collected near the village of Cocholgue, and a second juvenile specimen from Quiriquina Island. Prior to these finds, Aristonectes was viewed as a monospecific genus, including only the enigmatic Aristonectes parvidens, the holotype of which consists of an incomplete skull and incomplete postcranium. Other material referred to the genus includes an incomplete juvenile skull and other postcranial material from the upper Maastrichtian of Antarctica, as well as a partial skull from the Quiriquina Formation of central Chile. The relationships of Aristonectes have been controversial, with competing theories assigning the genus to Cryptoclididae, Elasmosauridae, and Aristonectidae; however, there is a developing consensus that Aristonectes is a derived elasmosaurid, and this paper gives strong evidence for this view. Comparison of the specimen here studied with the holotype of A. parvidens demonstrates that A. quiriquinensis is a distinct species. The completeness of the adult skeleton allows the first confident size estimates for adult Aristonectes. It is a large plesiosaurian with a relatively large skull with numerous homodont teeth, a moderately long and laterally compressed neck, and relatively narrow trunk, with slender and elongate forelimbs. The two specimens are restricted to the upper Maastrichtian of central Chile, posing questions concerning the austral circumpolar distribution of different elasmosaurids towards the end of the Cretaceous.

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ACKNOWLEDGMENTS

D. Rubilar-Rogers, R. A. Otero, and S. Soto-Acuña are supported by the Antarctic Ring Project (Anillos de Ciencia Antártica ACT-105, Conicyt-Chile). F. R. O’Keefe was supported by funds from the Marshall University Department of Biological Sciences, College of Science, and a John Deever Drinko Research Fellowship. W. Stinnesbeck gratefully acknowledges support by the Deutsche Forschungsgemeinschaft (grant STI 128/20–1). Special acknowledgments go to M. Reguero and Z. Gasparini (Universidad de La Plata, Argentina) for the access to the holotype of A. parvidens and the good will and help provided. P. Druckenmiller and R. Benson are gratefully acknowledged for their critical reviews of the manuscript and the very valuable comments that helped to improve it. Field work at Cocholgüe was executed in March 2009 by a student group of the Departamento de Geociencias of the Universidad de Concepción, headed by A. Quinzio-Sinn and C. Salazar. K. E. Buldrini, J. Alarcón (Laboratorio de Zoología de Vertebrados, Facultad de Ciencias, Universidad de Chile), and D. Delgado (Universidad CES y Escuela de Ingeniería de Antioquia, Colombia) are acknowledged for their excellent work on the preparation of the specimen.

Handling editor: Randall Irmis