New materials of Argentoconodon fariasorum (Mammaliaformes, Triconodontidae) from the Jurassic of Argentina and its bearing on triconodont phylogeny

ABSTRACT

Argentoconodon fariasorum is the only triconodont from the Jurassic of South America. Originally described on the basis of an upper molariform, A. fariasorum is now known by several specimens, including one that preserves most of its dentition, upper and lower jaws, and several postcranial elements. Close anatomical similarity exists between Argentoconodon fariasorum, Ichthyoconodon jaworowskorum, from the Cretaceous of Morocco, and the likely Jurassic Volaticotherium antiquus, from China. The results of a phylogenetic analysis including most taxa relevant to addressing triconodont phylogenetic relationships show Argentoconodon and Volaticotherium as a clade, which in turn is more closely related to Ichthyoconodon than to any other taxon. Our most parsimonious hypotheses support a triconodontid ancestry for Argentoconodon, Ichthyoconodon, and Volaticotherium as members of the monophyletic traditional subfamily Alticonodontinae. The inclusion of Argentoconodon among alticonodontines extends the geographical and temporal distribution of this triconodont subfamily to the South American Early Jurassic, resulting in extensive ghost lineages for many triconodontid groups. Postcranial similarities between Argentoconodon and Volaticotherium make it possible that the Argentinean taxon might have had gliding capabilities; if this is the case, our cladistic analysis highlights the possible existence of a gliding clade of triconodonts of wide distribution from at least as early as the Early Jurassic.

ACKNOWLEDGMENTS

This project has been funded by NSF DEB0946430 and ATOL 0629959, Agencia de Promoción Científica y Tecnológica (PICT 2006-01756), CONICET (Beca de Postgrado de Tipo I to LCG), and travel grants to LCG from the Richard Gilder Graduate School, the Museum of Comparative Zoology, the National Museum of Natural History, and the Yale Peabody Museum of Natural History.

We thank the Secretaría de Cultura del Chubut, the Museo Paleontológico “Egidio Feruglio,” the Escuela Rural No. 31, and the Farias family for providing permits and being gracious hosts. The field work was possible only due to the commitment and hard work of many people, among them: A. Lecuona, D. Pol, G. Turazzini, I. Maniel, J. Leardi, J. Sterli, L. Austin, L. Canessa, L. Chornogubsky, M. Cardenas, M. Becerra, M. de la Fuente, P. Puerta, and R. Gomez. Fossil preparation and casting were skillfully done by Leandro Canessa, Marcelo Isasi, and Maximiliano Iberlucea. Access to comparative material was allowed by Dr. D. Brinkman, Dr. M. Carrano, Dr. J. Cundiff, Dr. F. Jenkins Jr., Dr. A. Kramarz, Dr. P. Makovicky, Dr. J. Meng, Dr. C. Norris, Dr. E. Ruigomez, and Dr. W. Simpson. Version 1.1 of TNT was freely granted through the sponsorship of the Willi Henning Society.

We are most grateful to the reviewers and editors (Dr. Cifelli, Dr. Luo, and Dr. Martin), their suggestions greatly improved the quality of this paper. Finally, we thank Dr. C. Corbitt for improving the English of the manuscript.

This is the contribution R-17 of the Instituto de Estudios Andinos Don Pablo Groeber.

Handling editor: Thomas Martin