Pliocene Pre-GABI herbivorous mammals from Espinar, Peruvian Andean Plateau

Pliocene South American mammals prior to the Great American Biotic Interchange comprise the evolutionary pinnacle of a long-lasting process of continental isolation, in which large-scale orogeny and climate change were instrumental. These processes resulted in unique assemblages of extinct groups with peculiar anatomies. However, interpretation of the functional roles that these organisms would have played in the ecosystem is challenging because well-preserved fossils of this time interval in South America are scarce. Here, we describe a new Early Pliocene assemblage of native herbivorous megamammals documented by skeletons in anatomical connection from the Peruvian Andean plateau (city of Yauri in Espinar, Cusco Department). Fossil-bearing deposits pertain to Member C of the El Descanso Formation dated at 4.75 ± 0.5 Ma, when the plateau attained near-modern elevations and a Puna-type plant ecosystem. The mammal assemblage is dominated by xenarthrans, including three ground sloths (cf. Megatheriops rectidens, Simomylodon uccasamamensis, and Proscelidodon sp.) and Andinoglyptodon mollohuancai gen. et sp. nov., the first Pliocene glyptodontine known by a well-preserved cranium and dermal armor. Notoungulates are represented by the toxodontid Posnanskytherium viscachanense. Both selective and bulk feeders are identified, suggesting the existence of diverse plant resources in the Pliocene Puna ecosystem. These native mammals constituted the typical Pliocene herbivorous guild of the central Andean plateau and provide an opportunity to investigate the structure of mammalian communities just before the arrival of Holarctic immigrants.