Abstract

GOIN, Francisco et al. South american Metatherians from the begining of the Neogene (Early Miocene, Colhuehuapan Land-Mammal Age): Part 1: Introduction, Didelphimorphia and Sparassodonta. Ameghiniana [online]. 2007, vol.44, n.1, pp.29-71. ISSN 1851-8044.

This work is the first, of a series of three, taxonomic reviews of the Early Miocene (Colhuehuapian Land-mammal Age) South American metatherians. Colhuehuapian levels from the Gran Barranca south of the Colhue Huapi lake (Sarmiento Department, Chubut Province, Argentina) are the richest ones in specimens of this age. Colhuehuapian landscapes from Central Patagonia developed in a coastal plain located in a peninsular area, which originally suffered an intense erosion and subsequentely was agradded with fluvial and loessic (eolian) sediments. Palinomorphs and phytoliths suggest a period characterized by significant environmental changes, from xeric (middle Early Miocene) to humid-warm conditions (late Early Miocene). In uplands or areas far from the sea, temperate-humid closed forests prevailed, but in lowlands or litoral areas herbaceous (grass) plants and shrubs dominated, with subordinated or patchy arboreal vegetation. Paleoclimate would have been warm-temperate to warm and probably subhumid, more rainy in highlands. The most important results of this analysis are: (1) the oldest record of Didelphoidea didelphimorphians, including, probably, the oldest known caluromyid; (2) the recognition of a great diversity of carnivores belonging to the Order Sparassodonta, including the oldest record of a Thylacosmilidae; (3) the recognition of a new species of the incertae sedis mammal Necrolestes. Among the taxa reviewed here we describe the new species Necrolestes mirabilis.

Keywords : South America; Patagonia; Early Miocene; Colhuehuapian Age; Marsupialia; Didelphimorphia; Sparassodonta.