A partial skeleton of Typotheriopsis chasicoensis (Mesotheriidae, Notoungulata): The first accurate mammal record from the La Pilona Formation (Late Miocene), Cacheuta basin, central-western Argentina

Abstract

A partial skeleton of Mesotheriidae was recovered from the La Pilona Formation, cropping out in the core of the Tupungato Anticline, Cacheuta Basin, northern Mendoza Province (Argentina). This finding constitutes the first accurate fossil mammal from this unit, referred to the early Late Miocene (Tortonian; Chasicoan Stage/Age). The comparative study of the specimen IANIGLA-PV 1203 allows its determination as Typotheriopsis chasicoensis; many postcranial elements are herein described for the first time for this species, as well as for the compared T. silveyrai from the Río de los Pozos Formation in the same area. The body mass of IANIGLA-PV 1203 is calculated around 73 kg. The presence in Mendoza of T. chasicoensis expands the geographical distribution of the species, originally defined from the Arroyo Chasicó locality (Buenos Aires Province) and later recognized in localities of La Pampa Province, from sediments of the Cerro Azul Formation. The numerical ages constraining La Pilona Formation agree with the age of the Arroyo Chasicó locality. In La Pampa, T. chasicoensis is present at Cerro La Bota, assigned to the Chasicoan Stage/Age based on the faunal assemblage, but also in Algarrobo del Águila and Telén that are transitional and early Huayquerian in age, respectively. Typotheriopsis silveyrai is recognized in Huayquerian levels of Mendoza, Catamarca, and La Pampa provinces, and Typotheriopsis sp. in Chasicoan levels of La Rioja Province.