<i>Hiskatherium saintandrei</i>, gen. et sp. nov.: an unusual sloth from the Santacrucian of Quebrada Honda (Bolivia) and an overview of middle Miocene, small megatherioids

Abstract

ABSTRACT 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. ACKNOWLEDGMENTS We thank J. Geisler and four reviewers, H. G. McDonald, R. Salas-Gismondi, and two anonymous reviewers, for their thorough comments and suggestions, which helped improve the manuscript. We thank the following colleagues for facilitating access to fossil collections under their care: A. Kramarz (MACN), C. Cartelle (MCL), M. Reguero and S. Bargo (MLP), and C. Argot, C. De Muizon, and P. Tassy (MNHN). We express our gratitude to D. Croft (Case Western Reserve University, Cleveland, U.S.A.) for the information of Xyophorus specimens from Quebrada Honda housed in the University of Florida, Cyrielle Goillot (Université de Toulouse, Toulouse, France) for the pictures of the specimens housed in the Universidad Nacional de Colombia, and C. de Muizon (MNHN) who allowed us to reproduce pictures of holotype of Thalassocnus natans. We are extremely grateful to Jorge Gonzalez for creating the beautiful reconstruction of Hiskatherium and for his advice on the Miocene map. For one of us (F.P.), partial financial support came from the IFEA (2003–2006 postdoctoral fellowship), IRD mission in Bolivia and Cultural Service of the French Embassy in Bolivia (2007–2008 grants), and CONICET (2008–2010 postdoctoral fellowship). Handling editor: Jonathan Geisler