CONICET | Buscador de Institutos y Recursos Humanos

The territory of the Chubut province, Agentna, is one of the richest regions in vertebrate fossils from the Lower and Middle Cenozoic of South America. In many of its classic localities there are several successive fossil levels superimposed and associated with sediments of volcanic origin that allow a precise chronological control. During this (essentially Paleogene) time period, at least two important occur in the history of vertebrates worldwide phenomena: (1) an initial radiation and diversity that coincides with the Early Eocene Climate Optimum; (2) a turnover, or at least substantive modifications in the diversity and frequency of many clades, which occurs since the late Eocene and is defined towards the Eocene-Oligocene limit, a coincidentally with the abrupt global cooling event known as "Oi1". Since the beginning of the Miocene, the successive vertebrate faunas (especially continental mammals) express a modern character and, in many cases, a dramatic contrast with those of the Paleogene. For the Eocene-early Miocene period we cite the 513 species of continental vertebrates recognized for Chubut, which are distributed in the following faunal associations: Riochican, "Sapoan", Vacan, Barrancan, Casamayoran, Mustersan, Tinguirirican, Pre-Deseadan, Deseadan, Colhuehuapian, and ?Pinturan.? We synthesize the most relevant facts associated with the vertebrate fauna of this period of time, in an environmental and evolutionary climatic context. The more than 500 species of vertebrates that are recognized today from different faunas and localities within the Eocene-early Miocene sediments in the province of Chubut, clearly testify to the richness and relevance of these deposits.Key Words: Eocene- early Miocene, Vertebrates, Chubut Province, Patagonia

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