LOS ROEDORES DE LA FORMACION COLLON CURA (MIOCENO: MEDIO), Y LA IGNIMBRITA PILCANIYEU. CAÑADON DEL TORDILLO, NEUQUEN

Abstract

THE RODENTS OF COLLON CURA FORMATION (MIDDLE MIOCENE) AND THE PILCANIYEU IGNIMBRITE. CAÑADON DEL TORDILLO, NEUQUEN. Collón Cura Formation has been identified in this area by the presence of Pilcaniyeu Ignimbrite (Middle Member). The Upper and Lower Members of this formation, where fossils were found, are mainly reworked pyroclastic rocks, probably deposited simultaneously with the ignimbrite. Pedogenetic features are common, especially in the Lower Member, where basal strata show slightly different features. The following taxa are described: Neosteiromys ? tordillense gen. et sp. nov. (Erethizontidae); Maruchito trilofodonte gen. et sp. nov., Protacaremys denisae sp. nov.. Acarechimys sp. (Echimydae) and Dasyproctidae indet. They provide a better characterization of the Colloncuran s.s. which is restricted to the fauna of Collón Cura Formation associated to the Pilcaniyeu Ignimbrite. Based on the rodents, the following sequence of faunas is proposed: Santacrucian, Frisian S.S., Colloncuran s.s. and Mayoan. The Mayoan rodents have affinities with those of the Chasicoan, while the rodents of the other faunas are more related to each other. Our study suggests a hiatus within the Friasean Land-Marnmal Age. Rodents found at this locality, together with the presence of primates, sedimentological features, and other geological evidences for other regions of Patagonia, are indicative of warmer and more humid climatic conditions than previously postulated for the Friasian in Patagonia.