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The first Eocardiidae (Rodentia) in the Colhuehuapian (early Miocene) of Bryn Gwyn (northern Chubut, Argentina) and the early evolution of the peculiar cavioid rodents

2010; Taylor & Francis; Volume: 30; Issue: 2 Linguagem: Inglês

10.1080/02724631003618223

1937-2809

María E. Pérez, Marı́a Guiomar Vucetich, Alejandro Kramarz,

Bat Biology and Ecology Studies

ABSTRACT ABSTRACT Caviidae and Hydrochoeridae (extant Cavioidea s.s.), probably the most peculiar among rodents, are characterized by their evergrowing double-heart-shaped cheekteeth. They have classically been rooted in Eocardiidae, which ranges from Deseadan to 'Colloncuran' (late Oligocene–middle Miocene) in Patagonia, although in the Deseadan and Colhuehuapian (early Miocene) remains are very scanty. For the Colhuehuapian, only one species coming from the southern cliff of the Colhué Huapi Lake (Gran Barranca, Chubut, Argentina) was known so far. In this paper, the first Colhuehuapian eocardiids from outside Gran Barranca are reported: Luantus minor, sp. nov., and Chubutomys leucoreios, sp. nov. They are represented by two fragmentary mandibles and a few isolated cheek teeth, from the Trelew Member of the Sarmiento Formation at Bryn Gwyn, lower valley of the Chubut River, Chubut. The new species enlarge the knowledge of eocardiid diversity, and reinforce the hypothesis of a basal dichotomy for the group. L. minor represents one of the smallest species of the series Asteromys + Luantus + Phanomys + Eocardia, which likely gave rise to modern Cavioidea s.s. C. leucoreios pertains to a group of species with precocious hypsodonty and apparently low diversity, but without modern descendant. ACKNOWLEDGMENTS We thank Carolina Vieytes (MLP) for her valuable comments about this research, and Cecilia Deschamps (MLP) for improving the English version; Jaime Groizard (ALUAR) for his technical work in the MEB, the curators Eduardo Ruigómez (MPEF) and Marcelo Reguero (MLP) for access to material under their care, Rosario Romero (MPEF) for illustration of C. leucoreios, sp. nov., specimen, and the technicians of MPEF for their laboratory work.