A new enigmatic Late Miocene mylodontoid sloth from northern South America.

Ascanio D Rincón,Damián Ruiz-Ramoni,H Gregory Mcdonald,Andrés Solórzano,Mónica Núñez Flores

doi:10.1098/rsos.140256

Abstract

A new genus and species of sloth (Eionaletherium tanycnemius gen. et sp. nov.) recently collected from the Late Miocene Urumaco Formation, Venezuela (northern South America) is herein described based on a partial skeleton including associated femora and tibiae. In order to make a preliminary analysis of the phylogenetic affinities of this new sloth we performed a discriminate analysis based on several characters of the femur and tibia of selected Mylodontoidea and Megatherioidea sloths. The consensus tree produced indicates that the new sloth, E. tanycnemius, is a member of the Mylodontoidea. Surprisingly, the new taxon shows some enigmatic features among Neogene mylodontoid sloths, e.g. femur with a robust lesser trochanter that projects medially and the straight distinctly elongated tibia. The discovery of E. tanycnemius increases the diversity of sloths present in the Urumaco sequence to ten taxa. This taxon supports previous studies of the sloth assemblage from the Urumaco sequence as it further indicates that there are several sloth lineages present that are unknown from the better sampled areas of southern South America.

Highlights

South America was an island continent through most of the Cenozoic until the establishment of the Panamanian land bridge connecting Central and South America approximately 2.8 Ma [1,2,3]
We agree that H. ruetimeyeri, H. longiceps and A. giganteus are more closely related to primitive Megatherioidea than to members of the Mylodontoidea, but it is remarkable that the general morphology of their femur and tibia resembles those of later Mylodontoidea
E. tanycnemius retains some basal mylodontid features, or it is possibly extremely derived given that all other sloths have a short tibia relative to the length of the femur

Summary

Introduction

South America was an island continent through most of the Cenozoic until the establishment of the Panamanian land bridge connecting Central and South America approximately 2.8 Ma [1,2,3]. The isolation of South America as an island continent. Resulted in the evolution of a number of distinctive endemic linages of mammals. One of these 2 is the Xenarthra, which today includes anteaters (Vermilingua), armadillos (Cingulata) and sloths (Phyllophaga) [4]. Within the Xenarthra, sloths are an extremely diverse lineage in terms of the number of species (more than 90 named genera) [5,6], a wide range of body sizes and a diversity of locomotor and feeding adaptations, which is reflected in the variety of habitats in which they lived [4,7,8,9]

Objectives

Methods

Findings

Discussion

Conclusion