Anatomy of Condorchelys antiqua Sterli, 2008, and the origin of the modern jaw closure mechanism in turtles

ABSTRACT

Here we present a detailed anatomical description of cranial and post-cranial remains of a Jurassic turtle, Condorchelys antiqua Sterli, 2008, from the Cañadón Asfalto Formation (Middle Jurassic) in central Patagonia. Although C. antiqua is similar in morphology to the Early Jurassic turtles Kayentachelys aprix and Indochelys spatulata, it differs in that it lacks both pterygoid teeth and a V-shaped suprapygal 2, respectively. In light of new discoveries and reinterpretations of other fossil taxa, we suggest that several changes in the evolution of the skull morphology of turtles (such as the closure of the basipterygoid articulation, the closure of the interpterygoid vacuity, the development of the secondary lateral wall in the braincase, the development of temporal emargination and/or the posterior extension of the crista supraoccipitalis) could be related to the acquisition of a stronger skull to accommodate the modern pulley system. The optimization of these characters in a phylogenetic framework shows that they are coincident with the appearance of trochlear systems (oticum or pterygoidei) in turtles, suggesting a functionally correlated relationship among them.

ACKNOWLEDGMENTS

We thank G. W. Rougier (University of Louisville, U.S.A.) and R. Cúneo (Museo Paleontológico Egidio Feruglio [MEF], Argentina) for access to the specimens described herein; and all technicians at MEF for fossil preparation; J. González is acknowledged for the drawings; S. Chapman (Natural History Museum, U.K.), E. S. Gaffney and C. Mehling (American Museum of Natural History, U.S.A.), W. G. Joyce (Yale Peabody Museum, U.S.A.), C. Meyer (MH, Switzerland), J. Müller (Humboldt-Universität zu Berlin Museum für Naturkunde, Germany), E. Ruigómez (MEF, Argentina), and R. Schoch (Staaliches Museum für Naturkunde Stuttgart, Germany) are thanked for access to collections; J. Anquetin (Natural History Museum) is thanked for allowing us to see Pleurosternon bullockii while it was under his study. We also want to thank M. S. Fernández (Museo de La Plata, Argentina) for reading an early version of the manuscript. E. S. Gaffney, W. G. Joyce, S. P. Modesto, and two anonymous reviewers are thanked for their valuable comments on this paper. Raven Carper (University of California, Davis) made useful corrections to the English grammar. This work was partially supported by the Richard Estes Memorial Grant and a DAAD fellowship to J.S., by PICT (Proyecto de Investigación Científica y Tecnológica) grant 25276 (to Dr. Z. Brandoni), PICT 1756 (to Dr. D. Pol), and PIP (Proyecto de Investigación Plurianual) grant 112–200801-00795 (to M.D.F.).