Primeros hallazgos del équido Hippidion (Perissodactyla) en el Pleistoceno de la provincia de Mendoza, Argentina

Resumen

First records of the equid Hippidion (Perissodactyla) in the Pleistocene of Mendoza
province, Argentina. We report the first records of the horse Hippidion in Mendoza province (Argentina).
They come from two different localities, Uspallata and El Carrizal, both located near the city of Mendoza. The
fossils from Uspallata consist of dental elements of a single, young adult individual (16 incisor-canine fragments,
right P2-M2, left P2-M1 and fragments of left M3, right lower p2-p3, and left lower p3), stored at the Museo de
Ciencias Naturales y Antropológicas J. C. Moyano in Mendoza (MCNAM-PV 3808). They were found at the
northwestern extreme of the Cordón del Plata, southern Uspallata valley, in the Cordillera Frontal. Remains
appeared in silt-sandy levels of an impounding paleo-lake generated from the Piedras Blancas rock avalanche.
Stratigraphic studies carried out in this region indicate both, rock avalanche and lake deposits, are late Pliocene-
Middle Pleistocene in age, because overlying ash levels could be correlated by geochemistry analyses with another
close ash layers previously dated by Ar39/Ar40 method 350±80 Ky. In turn, the presence of an equid states a
maximum age younger than 2.5 Ma, or late Pliocene. The specimen from El Carrizal is a well-preserved first
central phalange, found by local people in the sourroundings of El Carrizal dam, about 70 km south of Mendoza
city. Morphological features (oval protocone, rounded protoconid and hypoconid, reduced metaconid-metastylid
double knot) allow the teeth from Uspallata to be ascribed to the genus Hippidion Owen. Similarly, the phalange
(1FIII) from El Carrizal presents the morphology of this genus (strong muscular insertions), in contrast to the
genus Equus (Amerhippus) Hoffstetter. Species of Hippidion are mainly differentiated by the leg bones, the
dentition being very homogeneous and just showing differences in size. Even though postcranial remains would
allow a fully reliable determination, the tooth size and hipsodonty of the Uspallata specimen, as well as its
stratigraphic origin (older than late Pleistocene), supports its determination as H. devillei (Gervais). At the
same time, the morphology and dimensions of the phalange also support its ascription to this species. Hippidion
devillei has been found in Jujuy, San Luis, and Buenos Aires provinces. Its presence in Mendoza supports a
space-temporal distribution in a North-Southeast way during the latest Pliocene or early-middle Pleistocene.