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

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Abstract

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.

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Acknowledgments

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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Authors and Affiliations

  1. Departamento de Paleontología, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CCT-CONICET-Mendoza, Avda.Ruiz Leal s/n, Parque Gral. San Martín, 5500, Mendoza, Argentina

    François Pujos

  2. Institut Français d’Etudes Andines (IFEA), Casilla 18-1217, Av. Arequipa, 4595, Lima 18, Perú

    François Pujos

  3. Department of Biological and Environmental Sciences (Department 2653), University of Tennessee at Chattanooga, 615 McCallie Avenue, Chattanooga, TN, 37403-2598, USA

    Timothy J. Gaudin

  4. Department of Ecology and Evolutionary Biology, University of Toronto, 25 Harbord Street, Toronto, Ontario, M5S 3G5, Canada

    Gerardo De Iuliis

  5. PUC Minas, Avenida Dom José Gaspar, 290 Coração Eucarístico, Belo Horizonte, Minas Gerais, Brazil

    Cástor Cartelle

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  1. François Pujos
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  2. Timothy J. Gaudin
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  4. Cástor Cartelle
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Correspondence to François Pujos.

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Pujos, F., Gaudin, T.J., De Iuliis, G. et al. Recent Advances on Variability, Morpho-Functional Adaptations, Dental Terminology, and Evolution of Sloths. J Mammal Evol 19, 159–169 (2012). https://doi.org/10.1007/s10914-012-9189-y

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