Megatherioidea (Mammalia, Xenarthra, Tardigrada) from the Pinturas Formation (Early Miocene), Santa Cruz Province (Argentina) and their chronological implications

Pyro clastic and epiclastic continental sediments bearing the fauna Astrapothericulense from the Pinturas Formation of Ameghino crop out mainly at several localities at the upper valley of the Pinturas River and its tributaries, northwestern Santa Cruz Province, Argentina. These continental sediments are referred to the Burdigalian Stage and constitute the basis for the recognition of the Pinturas Formation. The fauna recorded in the Pinturas Formation mainly consists of mammals, specially rodents, native ungulates, xenarthrans and primates. Here we describe the first association of Megatherioidea (Mammalia, Xenarthra, Tardigrada) from different localities of the Pinturas Formation with accurate geographic and stratigraphic provenance. The Megatherioidea from the Pinturas Formation presented herein are represented by (1) Schismotherium cf. binum; (2) Hapalops sp.; and (3) a Megatherioidea indet. In addition, the holotypes of Schismotherium binum (MACN A 11750), Hapalops curvus (MACN A 11140), and Pelecyodon arcuatus were collected from the fauna Astrapothericulense of Ameghino; unfortunately, it is not easy to determine if they were collected from the Pinturas Formation since they are part of Ameghino's Collection (MACN), but were collected a time when the Pinturas Formation had not yet been proposed. The presence of a species of Schismotherium and of Hapalops in the Pinturas Formation represent accurate early records for these genera, but not necessarily the earliest. The age of the Pinturas Formation could overlap, partially or totally, with the age of the Santa Cruz Formation at the Atlantic coast, where most Early Miocene Megatherioidea were collected.