Lagostomus maximus (Desmarest) (Rodentia, Chinchillidae), the extant plains vizcacha in the Late Pleistocene of Uruguay

Abstract

Ubilla, M. & Rinderknecht, A., April 2016. Lagostomus maximus (Desmarest) (Rodentia, Chinchillidae), the extant plains vizcacha in the Late Pleistocene of Uruguay. Alcheringa 40, xxx–xxx. ISSN 0311-5518

The extant plains vizcacha, Lagostomus maximus, is described from the Late Pleistocene (Dolores Formation) of Uruguay based on an almost complete articulated skeleton. It is compared with the nominally extinct Pleistocene species of the genus. An AMS ¹⁴C taxon-age is determined for L. maximus at 11 879 ± 95 years BP (cal. BP 13 898–13 941). Lagostomus maximus is absent from modern mammal communities in Uruguay, and no Holocene evidence is available. Because L. maximus exhibits remarkable sexual and ontogenetic dimorphism, we examined a range of juvenile, sub-adult and adult male and female specimens. It is not possible to differentiate the articulated Pleistocene fossil from sub-adult specimens of L. maximus based on this sample. Moreover, the skull characteristics, including a broad vertical ramus of the zygomatic arch, semi-circular temporal crest and short robust sagittal crest, most closely resemble extant female individuals. Molar size is non-predictive for ontogenetic stage or body mass because it reaches stability during early adulthood. Other fragmentary skull remains are herein assigned to L. sp. cf. L. maximus. Lagostomus cavifrons from the Pleistocene of Argentina is considered synonymous with L. maximus. Its character states concur with the range of intraspecific variability and it has been established on a young adult or adult male individual. Likewise, the other Argentinean Pleistocene species based on incomplete mandibles, L. angustidens, L. striatus, L. heterogenidens, L. egenus, L. minimus and L. debilis, concur with ontogenetic morphs and are here assigned to Lagostomus sp. The ecological preferences of extant L. maximus infer open arid or semi-arid landscapes for the latest Pleistocene of southern Uruguay. This hypothesis is reinforced by the coeval presence of Microcavia, Galea and small camelids in the same strata. The Last Glacial Maximum likely promoted this environmental setting. Latest Pleistocene or early Holocene climatic change might have facilitated local extinctions and/or range shifts among this mammal fauna.

Martín Ubilla [[email protected]], Facultad de Ciencias, Universidad de la Republica, Iguá 4225, 11400, Montevideo, Uruguay; Andrés Rinderknecht [[email protected]], Museo Nacional de Historia Natural, Paleontología, 11000, Montevideo, Uruguay.

Key words:

• Pleistocene
• Lagostomus maximus
• Uruguay
• taxon-age

Acknowledgements

A. Sánchez (San Ramón) allowed us to study the fossil material. The curators D. Verzi (Mastozoología, La Plata), D. Flores and S. Lucero (Mastozoología, Buenos Aires), R. Portela-Miguez (Mammals Section, London), M. Reguero (Paleontología de Vertebrados, La Plata), A. Kramarz (Mamíferos fósiles, Buenos Aires), S. Maris (Mamíferos fósiles, Buenos Aires) and E. Gonzales (Mamíferos, Montevideo) facilitated the access to the comparative material of the collections. Two anonymous reviewers and Editors (S. McLoughlin and B. Kear) significantly improved the manuscript. L. Rasia (La Plata) provided invaluable comments on the variability of L. maximus and E. Ferrari provided archaeological information for Uruguay. This is a contribution to CSIC-C-211-348 (Ubilla).