HISKATHERIUM SAINTANDREI, GEN. ET SP NOV.: AN UNUSUAL SLOTH FROM THE SANTACRUCIAN OF QUEBRADA HONDA (BOLIVIA) AND AN OVERVIEW OF MIDDLE MIOCENE, SMALL MEGATHERIOIDS

A dentary from the Laventan SALMA (middle Miocene) of Quebrada Honda, Bolivia, recognized as a new, small member of Megatherioidea (Hiskatherium saintandrei, gen. et sp. nov.), is reported. This taxon is clearly distinct from Nothrotheriidae and Megalonychidae and has affinities with Hapalops and Xyophorus. It is characterized by m1-m4 without diastema; strong hypsodonty (HI = 0.93); m1-m3 constituted by two transverse lophids separated by a deep, transverse, and labially open valley; m4 round with distal lophid mesiolingually-distolabially extended and without vertical groove; m2-m3 with lingual and labial vertical grooves; and the posteroventral margin of symphysis located anteriorly to m1. Although Hiskatherium and Diabolotherium have a similar dental formula, the 'megatheriine-shaped' teeth of Diabolotherium do not support a close phylogenetic relationship between Hiskatherium and Diabolotherium. Their dental formulae suggest that both genera were selective feeders, capable of consuming tough items. Hiskatherium, like most other sloths, has lower molariform teeth that have a mesial and a distal lophid; the former has a mesial cuspid 'A,' located at the center of the mesial lophid, and the latter has distolingual ('B,' or lingual) and distolabial ('C') cuspids at each end. This terminology permits a straightforward nomenclature based on cusp/cuspid position and facilitates comparisons among Tardigrada.