New data on the Diversity and Chronology of the Late Miocene Xenarthra (Mammalia) from Ecuador

Abstract

Xenarthra are an endemic and relictual clade of Placentalia that played an important role in the biodiversity during the Cenozoic in today South America. Fossil forms representing close to 200 genera have been identified, both Pilosa and Cingulata, during its long evolutionary history (late Paleocene/early Eocene–Recent). However, there is an evident imbalance in what concerns the knowledge of the xenarthrans of southern South America compared with those of middle and low latitudes, of which little is known, despite the fact that in recent times the studies of these latter have been greatly improved. New remains of Xenarthra (Folivora Mylodontinae gen. et sp. indet. and Cingulata Glyptodontidae gen. et sp. indet.) from the Letrero Formation, upper Miocene (ca. 11–9 Ma, Tortonian) of southern Ecuador are here reported and described. The only previous record from this formation belongs to the Cingulata Dasypodidae Anadasypus aequatorianus. Our comparative study reveals several morphological differences compared with other known Miocene specimens, especially those of La Venta (Colombia), Anzoátegui and Urumaco (Venezuela), and the Patagonian region (Argentina). These morphological differences suggest that these remains could belong to new taxa, and highlight the fact that, despite the relative proximity, both chronological and geographic, of the middle Miocene of La Venta (Colombia, ca. 13–11 Ma, Serravallian to Tortonian), the Xenarthra registered in Ecuador are morphologically distant, suggesting some isolation of this putative endemic paleofauna.