New specimen of Pucatherium parvum (Xenarthra, Dasypodidae), a singular dasypodid of the Paleogene (Eocene) of northwest Argentina: importance in the early evolution of armadillos

ABSTRACT

A new specimen of Pucatherium parvum from the lower levels of the Upper Lumbrera Formation of Salta Province is reported. An almost complete dorsal carapace and several postcranial remains were preserved, providing important information about this particular taxon. The specimen is comparable in size to Dasypus novemcinctus, although the osteoderms are very small. The dorsal carapace seems to be completely integrated by movable osteoderms, providing a high degree of mobility in the anteroposterior axis. There is no evidence of pseudoshield, scapular shield, or pelvic shield. The dating of 39.9 ± 0.4 Ma (U-Pb zircon), taken from a tuff close to the top of the Upper Lumbrera Formation, allows us to refer this record of P. parvum to the middle Eocene (Bartonian). This, together with its broad geographic distribution, allows correlating the Upper Lumbrera Formation with the Quebrada de los Colorados Formation in Salta Province and with the Casa Grande Formation in Jujuy Province. On the other hand, the estimated depositional age of 37.3–35.4 Ma for the Geste Formation in Salta Province extends the biocron of P. parvum to the late Eocene.

ACKNOWLEDGMENTS

We thank M. Díaz (Colección Mamíferos Lillo), P. Ortiz (Colección Paleontología Vertebrados Lillo), and A. A. Carlini (Colección Laboratorio de Morfología Evolutiva y Desarrollo) for providing us with access to the collection under their care. Financial support was provided by the Consejo de Investigaciones de la Universidad Nacional de Tucumán (PIUNT 2018 G626), Consejo Nacional de Investigaciones Científicas y Tecnológicas (PICT-2016-3682, PICT-2016-1274), and partially by the University of La Plata, Argentina (Research project code: N-889 to M.R.C.). We thank L. Mercado and P. Camaño, from the Museum of Anthropology of Salta, Argentina, for providing exploration permissions, E. Guanuco and M. Armella for illustrations, and S. Nanni and D. García-López for the translation of the manuscript. We would like to thank the reviewers for their insightful comments on the paper, which improved the work. The authors also thank the Facultad de Ciencias Naturales e Instituto Miguel Lillo (Universidad Nacional de Tucumán) and the Fundación Miguel Lillo for research and facilities support.