Journal of Mammalian Evolution

, Volume 19, Issue 3, pp 159–169 | Cite as

Recent Advances on Variability, Morpho-Functional Adaptations, Dental Terminology, and Evolution of Sloths

  • François Pujos
  • Timothy J. Gaudin
  • Gerardo De Iuliis
  • Cástor Cartelle
Original Paper


The occasion of the Xenarthra Symposium during the ICVM 9 meeting allowed us to reflect on the considerable advances in the knowledge of sloths made by the “X-community” over the past two decades, particularly in such aspects as locomotion, mastication, diet, dental terminology, intraspecific variation, sexual dimorphism, and phylogenetic relationships. These advancements have largely been made possible by the application of cladistic methodology (including DNA analyses) and the discovery of peculiar forms such as Diabolotherium, Thalassocnus, and Pseudoglyptodon in traditionally neglected areas such as the Chilean Andes and the Peruvian Pacific desert coast. Modern tree sloths exhibit an upside-down posture and suspensory locomotion, but the habits of fossil sloths are considerably more diverse and include locomotory modes such as inferred bipedality, quadrupedality, arboreality or semiarboreality, climbing, and an aquatic or semi-aquatic lifestyle in saltwater. Modern tree sloths are generalist browsers, but fossil sloths had browsing, grazing, or mixed feeding dietary habits. Discovery of two important sloth faunas in Brazil (Jacobina) and southern North America (Daytona Beach and Rancho La Brea) have permitted evaluation of the ontogenetic variation in Eremotherium laurillardi and the existence of possible sexual dimorphism in this sloth and in Paramylodon harlani. A new dental terminology applicable to a majority of clades has been developed, facilitating comparisons among taxa. An analysis wherein functional traits were plotted onto a phylogeny of sloths was used to determine patterns of evolutionary change across the clade. These analyses suggest that megatherioid sloths were primitively semiarboreal or possessed climbing adaptations, a feature retained in some members of the family Megalonychidae. Pedolateral stance in the hindfoot is shown to be convergently acquired in Mylodontidae and Megatheria (Nothrotheriidae + Megatheriidae), this feature serving as a synapomorphy of the latter clade. Digging adaptations can only be securely ascribed to scelidotheriine and mylodontine sloths, and the latter are also the only group of grazing sloths, the remainder being general browsers.


Sloths Morpho-functional adaptations Sexual dimorphism Dental terminology Locomotion Phylogeny 



We thank Editor-in-Chief John Wible for agreeing to publish the proceedings of the symposium Form and Function of the Xenarthra (held in 2010 during the ICVM9 meeting in Punta Del Este, Uruguay) in the Journal of Mammalian Evolution. We also thank all of the participants in that symposium and in this volume for their excellent research and collegiality, which have made organizing the symposium and editing this volume such a pleasure for the first two authors of this manuscript (FP & TJG). We thank Jorge Gonzalez for providing the beautiful illustration of Pseudoglyptodon; John Wible and two anonymous reviewers for comments that greatly improved this work. Figure 2 is reproduced in part from Bargo et al. (2006a; Muzzle of South American Pleistocene Ground Sloths (Xenarthra, Tardigrada). J Morphol 267:248–263) with permission of John Wiley & Sons, Inc and the authors.


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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • François Pujos
    • 1
    • 2
  • Timothy J. Gaudin
    • 3
  • Gerardo De Iuliis
    • 4
  • Cástor Cartelle
    • 5
  1. 1.Departamento de Paleontología, Instituto Argentino de NivologíaGlaciología y Ciencias Ambientales (IANIGLA), CCT-CONICET-MendozaMendozaArgentina
  2. 2.Institut Français d’Etudes Andines (IFEA)Lima 18Perú
  3. 3.Department of Biological and Environmental Sciences (Department 2653)University of Tennessee at ChattanoogaChattanoogaUSA
  4. 4.Department of Ecology and Evolutionary BiologyUniversity of TorontoTorontoCanada
  5. 5.PUC MinasBelo HorizonteBrazil

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