ACKNOWLEDGMENTS

Funding for this research was provided by the Case Western Reserve University School of Medicine, the National Geographic Society Committee for Research and Exploration (NGS 8115-06 to D. Croft), and the National Science Foundation (EAR 0635678 to C. Garzione and T. Jordan). We thank R. Hulbert and B. MacFadden for the loan of UF 130883 and access to other Cerdas specimens in UF collections. Study of museum collections in Argentina was facilitated by M. Reguero (La Plata) and A. Kramarz (Buenos Aires). We gratefully acknowledge the field efforts of F. Anaya, D. Auerbach, J. Conrad, C. Garzione, P. Higgins, B. MacFadden, and J. Smith, who helped collect the UATF mesotheriine specimens from Cerdas included in our study; UATF specimens from Nazareno were collected by F. Anaya and R. Madden. Thanks to F. Anaya, J. Chick, A. Shinya, and L. Yerian for fossil preparation and curation. Thanks to M. Coleman of Midwestern University for discussions about petrosal morphology, C. Heesy of Midwestern University for discussions about cladistics, and to V. Guinto of Case Western Reserve University School of Medicine and I. Baum of the Tri-C West Scientific Imaging Program for building the interactive files for the movie of UF 133803. Thanks to our reviewers for providing helpful suggestions. Funding for this research was provided by the National Geographic Society and the Case Western Reserve University School of Medicine.