An enigmatic nothrotheriinae (Xenarthra, Tardigrada) from the Pleistocene of Argentina

Abstract

The aim of this contribution is to describe two femora (MACN Pv 14148 and MACN Pv 14149 ) recovered from the Pleistocene of Santa Fe Province Argentina, provided a taxonomic assignation for them, and to discuss some taxonomic and biogeographical aspects of these finds. The general morphology of the femora more closely resembles the femur of Nothrotheriops (Xenarthra, Tardigrada, Nothrotheriidae) than any of the other known South American late Pleistocene nothrotheriine. Although a bit larger, both specimens are also more similar in size to those of Nothrotheriops shastensis and share several features with this species. Based on their morphology the femora could be referred to Nothrotheriops, a genus exclusively recorded from the Pleistocene of North America, making this the first record of the genus outside of its known geographical distribution. However an alternative hypothesis is also plausible: the assignation of MACN Pv 14148 and MACN Pv 14149 to other Nothrotheriinae, e.g., Nothropus, which was recorded from the same beds of the femora but was determined on a mandibular fragment. Pending the discovery of associated skeletal material we are left we three possible options which cannot be resolved at this time: 1) the femora may be from Nothropus since the femur for that genus is unknown; 2) they may go with N. carcaranensis which is not Nothropus but we are not sure to what genus the type mandible should be assigned; or 3) they may in fact be from Nothrotheriops and thus the first evidence for the genus in South America.