New findings of fossil mammals from the early Miocene Cerro Bandera Formation (Neuquén province, Argentina). Biochronological and paleobiogeographical considerations

KRAMARZ, A.; FORASIEPI, A.; BOND, M.; GARRIDO, A.; ARNAL, M.; AGUIRREZABALA, G. ; FILLIPPI, L.

San Juan

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Museo de Ciencias Naturales Universidad Nacional de San Juan

The Cerro Bandera Formation is a Miocene continental succession exposed in isolated areas at the centre-East of Neuquén Province, Northwestern Patagonia, Argentina (Leanza and Hugo 1997). The sequence is 45 m thick, composed by primary and reworked pyroclastic deposits and scant sandstone levels, filling local paleovalleys excavated on Late Cretaceous and Paleocene rocks (Leanza and Hugo, 1997; Kramarz et al., 2005). Based upon its faunal content, this unit was referred to the Colhuehuapian SALMA (early Miocene) (Kramarz et al., 2005). Here we report a new mammal association derived from two new localities of the Cerro Bandera Formation situated at the northeastern slope of the Barda Negra (Zapala Department). The specimens are housed at Museo ?Prof. Dr. Juan A. Olsacher?, Zapala. Mammals from Loc. A (S 39° 02´ 06.3"/ W 69° 40´ 54.3") come from whitish-greyish tuffaceous levels, about six meters from the base of the stratigraphic section exposed in the area. Those from Loc. B (S 39º02?26.21?/ W 69º40?53.36) derive from similar rocks located about 25 meters from the exposed base. In contrast to other previously studied localities (Kramarz et al., 2005), the new ones provided more abundant and more complete remains. Many of the taxa newly recorded in both localities support a Colhuehuapian age [e.g. Colpodon Burmeister, 1885 (Notoungulata)]. However, the same deposits also provided some few taxa that are not represented in the typical Colhuehuapian and younger mammal associations from Central Patagonia, but in the immediately older Deseadan SALMA (late Oligocene) [e.g. Cephalomys Ameghino, 1897 (Rodentia), Archaeohyracidae (Ameghino, 1897) (Notoungulata)]. Although further studies and absolute datings are necessary, these new findings suggest that the Cerro Bandera mammal assemblage would document the survival in northern Patagonia of some mammals that already became extinct in central and southern Patagonia before the early Miocene. As an alternative interpretation, the Cerro Bandera assemblage would represent a transitional association between the typical Deseadan and Colhuehuapian faunas, corresponding to a pre-Colhuehuapian age, hitherto recorded anywhere else in South America.