Chronological correlation, paleoecology, and paleobiogeography of the late Cenozoic South American "Rionegran" land-mammal fauna: A review

ALBERDI, MARÍA TERESA; BONADONNA, FRANCESCO P.; ORTIZ JAUREGUIZAR, EDGARDO

Revista Española de Paleontología

Sociedad Española de Paleontología

Año: 1997 vol. 12 p. 249 - 255

0213-6937

The rise and fall of the Rionegran land-mammal fauna of the Río Negro Formation (northern Patagonia), are related to the regression of the "Paranean" Sea  (Middle to Late Miocene), and to the environmental changes brought about by the Andean diastrophic Diaguita Phase (Late Pliocene). A new fission track of 4.41 +-0.50  Ma has been obtained for the volcanic ash horizon in the upper part of the Río Negro Formation at the mouth of the Río Negro River. this places its mammal fauna at the begginning of the Montehermosan Land-Mammal Age (Pliocene), with a time range of ca. 6 to 3 Ma. Geological and biological evidences show that the Rionegran sediments exposed in the western area are older than the eastern ones, and can be assigned to the Huayquerian Land-Mammal Age (Late Miocene), ranginf approximately from 9 to 6 Ma. Outside South America, the Rionegran fauna can be correlated with the Hemphilian and early Blancan North American faunas, and with the Turolian and earliest Ruscinian faunas of Europe. Rionegran mammals lived in flood-plain environments characterized by pools and swamps, alternated with woodland and grasslands. Similarities of the Rionegran fauna with the apparently coeval ones of central, NE, and NW Argentina, indicate that subtropical environments conditions spread from northern Argentina to northern Patagonia during the Late Miocene-Pliocene.