Nothrotheriopssp. (Mammalia, Xenarthra) from the Late Pleistocene of Argentina: implications for the dispersion of ground sloths during the Great American Biotic Interchange

Abstract

The aim of this contribution is to describe a femur (MCRS199) assigned toNothrotheriopssp. from the Late Pleistocene of Santa Fe Province (Argentina), and discuss the implications of this find in the context of the dispersal of ground sloths during the Great American Biotic Interchange. The specimenMCRS199 is smaller than the femora referred to the North American speciesNothrotheriops texanusandNothrotheriops shastensisbut shares several features with these species: (i) shape and position of the greater trochanter, (ii) development of the lesser trochanter, (iii) presence of connection between the third trochanter and the ectepicondyle, (iv) distal third of the femur wider, withML/DWindex of 1.93, and (v) location and relationship of the distal condyles. These similarities allow us to assignMCRS199 toNothrotheriopssp. The record ofNothrotheriopssp. from Santa Fe Province chronologically coincides with the earliest records ofNothrotheriops shastensissuggesting a broad geographical distribution ofNothrotheriopsduring the Late Pleistocene, ranging from 33–36°N (e.g. states of California and Arizona,USA) to 31°S (northern Salado River, Santa Fe Province, Argentina). Thus,Nothrotheriopshave dispersed from North America (whereNothrotheriopshas early records, Calabrian–Middle Pleistocene) to South America where localities bearingNothrotheriopsare Late Pleistocene in age. In addition, once in South America and probably during the Middle Pleistocene,Nothrotheriopsprobably gave rise to its sister taxon,Nothrotherium, with records from the Middle Pleistocene (e.g. 223 kaBP, northeastern Brazil) to the Late Pleistocene (e.g. 15 kaBP).