FIRST MAMMALIAN REMAIN FROM THE MIDDLE MIOCENE ANGASTACO FORMATION AT THE TONCO VALLEY, LOS CARDONES NATIONAL PARK, SALTA PROVINCE, ARGENTINA

ZIMICZ, A.N.; FERNÁNDEZ, M.; FERNICOLA, J.C.; CHORNOGUBSKY, L.

Congreso; 3rd Palaeontological Virtual Congresss; 2021

The Angastaco Formation (Payogastilla Group) comprisesthick fluvio-eolian Oligocene-Miocene deposits that recordthe regional environmental changes promoted by the Andeanorogeny. An arid paleoenvironment has been suggested for thisunit based on geochemical data and the alleged absence offossils probably given by an oxidising depositional environment.Here, we describe the first mammalian remain exhumed fromthe lower part of Las Flechas Member at the Tonco Valley, LosCardones National Park (Salta Province, Argentina). The age ofthe fossiliferous strata is bracketed by absolute ages between17.5 and 13. 7 Ma (early-middle Miocene). The specimen IBIGEO-P128 is an isolated hypselodont left upper molar (probablyM1) identified here as Hegetotheriinae indet. (Notoungulata,Typotheria, Hegetotheriidae). This tooth is sub-trapezoidalin occlusal outline, being longer than wide; it exhibits a thickcement layer. The enamel layer is continuous around the crown,being much thinner at the mesio and disto-labial angles of thetooth; the labial face presents shallow, but conspicuous grooves;the lingual face is slightly convex without entoflexus; the distalface is smooth, and narrower than the remainder of the occlusalsurface; the distal face and the ectoloph form an angle ofapproximately 90°, and no fossettes are observed. This reportconstitutes the earliest record of the family Hegetotheriidaein northwestern Argentina. The hypselodont condition of thespecimen agrees with the suggested open environments for theunit. This discovery also emphasizes the need of exhaustive andsystematic prospections at the Angastaco Formation.