Youngest Interatheriinae (Mammalia, Notoungulata) from lower Pliocene Tunuyán Formation (Mendoza, Argentina)

Abstract

After several years of intense fieldwork in the area of Huayquerías del Este, northern Mendoza (Argentina), the results account for more than 1,000 specimens and 67 taxa of vertebrates documented from the Huayquerías and Tunuyán formations. In this contribution, we present the first record of an indeterminate Typotheria Interatheriinae coming from a fossil-bearing level in the lower section of the Tunuyán Formation, 10–15 m above the contact with the underlying Huayquerías Formation (5.84 ± 0.41 Ma, late Miocene; Messinian), which implies an interval age between the latest Miocene (upper Messinian) and early Pliocene (Zanclean) age for the lower levels of the Tunuyán Formation where the interathere remain comes from. The specimen (IANIGLA-PV 450) is a fragment of mandible with a broken right p3?, whose small size and features (shortening of the trigonid, a low trigonid-talonid length ratio <1, and a circular-outlined talonid) distinguish it from late Miocene species of Protypotherium (P. antiquum, P. distinctum, and P. minutum), but also from early and middle Miocene interatheres (e.g., Miocochilius, Interatherium, Caenophilus). We recognize it as an Interatheriinae indet., and based on the peculiar features of this specimen it could be a new taxon, but its fragmentary and isolated condition prevent us from providing an accurate diagnosis. IANIGLA-PV 450 is the first mention of an Interatheriinae for the Tunuyán Formation and the central-west region of Argentina, but also the Last Appearance Datum (LAD), latest Miocene–early Pliocene, for the group.