On the status of the giant mylodontine sloth Glossotherium wegneri (Spillmann, 1931) (Xenarthra, Folivora)from the late Pleistocene of Ecuador

Gerardo De Iuliis,François Pujos,Alberto Boscaini,Robert K Mcafee,Leonard J S Tsuji,Cástor Cartelle,Lorenzo Rook

doi:10.5852/cr-palevol2020v19a12

Abstract

The late Pleistocene mylodontine sloth Glossotherium wegneri (Spillmann, 1931) (Interandean region, Ecuador) has been assigned to Glossotherium Owen, 1839 and Oreomylodon Hoffstetter, 1949 (the latter ranked as a subgenus or genus), and synonymized with G. robustum (Owen, 1842). However, the phylogenetic and comparative analyses conducted here, which include previously undescribed remains, strongly suggest specific distinction for G. wegneri and that there is little, if any, support for generic or subgeneric distinction for Oreomylodon. Among the notable features of this species are the presence of an internasal element, marked expansion of the rostrum anteriorly, and dorsoventrally and the palatal region transversely, increased separation of the caniniform tooth from the anterior edge of maxilla, increased relative braincase width, relatively enlarged hypoglossal foramen, and greatly elongated zygomatic process of the squamosal. The resulting single MPT recovered a monophyletic Glossotherium, with the following phylogenetic arrangement of the species of this genus (G. robustum + ((G. wegneri + G. tropicorum Hoffstetter, 1952) + (G. phoenesis Cartelle, De Iuliis, Boscaini & Pujos, 2019 + G. tarijense Ameghino, 1902))).

Highlights

Sloths (Folivora synonym of Tardigrada synonym of Phyllophaga; Delsuc et al 2001; Fariña & Vizcaíno 2003) and anteaters (Myrmecophaga) constitute Pilosa, one of the main clades of Xenarthra, the other being the cingulates (Cingulata), which include armadillos, pampatheres, and glyptodonts
The present study focuses on a species of Mylodontidae, a clade known from the late Oligocene to the late Pleistocene of North and South America
The species studied here has been consistently considered as being very similar morphologically to species that have been assigned to the South American mylodontine Glossotherium, including G. robustum, G. tropicorum, and G. phoenesis, G. robustum, as is evident from the taxonomic history

Summary

Introduction

Sloths (Folivora synonym of Tardigrada synonym of Phyllophaga; Delsuc et al 2001; Fariña & Vizcaíno 2003) and anteaters (Myrmecophaga) constitute Pilosa, one of the main clades of Xenarthra, the other being the cingulates (Cingulata), which include armadillos, pampatheres, and glyptodonts. Sloths are currently represented only by the two small-sized genera Bradypus Illiger, 1811 and Choloepus Linnaeus, 1758, which are nearly exclusively arboreal, with peculiar upside-down locomotion, and restricted to the tropical rain forests of South and Central America Their fossil representatives document a much more taxonomically and ecologically diverse clade, with at least 90 named genera that ranged throughout much of the New World, South America, from the Oligocene to the Holocene (e.g. McDonald & De Iuliis 2008; Gaudin & Croft 2015). This arrangement reflects the longstanding consensus that this genus is the sister clade to the remaining sloths while the other living genus, the twotoed sloth Choloeopus, is included among megalonychids These osteologically-based hypotheses have been recently questioned by molecular data (i.e., Delsuc et al 2019; Presslee et al 2019), according to which Bradypus is closely related to Nothrotheriidae and Megatheriidae (i.e., Megatherioidea) and Choloepus to mylodontids

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