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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

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.

Keywords

Sloths Morpho-functional adaptations Sexual dimorphism Dental terminology Locomotion Phylogeny 

Notes

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.

References

  1. Antoine P-O, Salas-Gismondi R, Baby P, Benammi M, Brusset S, De Franceschi D, Espurt N, Goillot C, Pujos F, Tejada J, Urbina M (2007) The middle Miocene (Laventan) Fitzcarrald Fauna, Amazonian Peru. In: Díaz-Martínez E, Rábano L (eds) 4th European Meeting on the Palaeontology and Stratigraphy of Latin America, Madrid, pp 19–24Google Scholar
  2. Bargo MS (2001a) El aparato masticatorio de los perezosos terrestres (Xenarthra, Tardigrada) del Pleistoceno de la Argentina. Morfometría y biomecánica. Unpublished PhD thesis. Universidad Nacional de La Plata, La Plata, 400 ppGoogle Scholar
  3. Bargo MS (2001b) The ground sloth Megatherium americanum: skull shape, bit forces, and diet. Acta Palaeontol Pol 46:173–192Google Scholar
  4. Bargo MS (2003) Biomechanics and paleobiology of the Xenarthra: the state of the art (Mammalia, Xenarthra). In: Fariña RA, Vizcaíno SF, Storch G (eds) Morphological Studies in Fossil and Extant Xenarthra. Senckenb biol 83:41–50Google Scholar
  5. Bargo M, De Iuliis G, Vizcaíno SF (2006b) Hypsodonty in Pleistocene ground sloths. Acta Palaeontol Pol 51:53–61Google Scholar
  6. Bargo MS, Toledo N, Vizcaíno SF (2006a) Muzzle of South American Pleistocene ground sloths (Xenarthra, Tardigrada). J Morphol 267:248–263PubMedCrossRefGoogle Scholar
  7. Bargo MS, Vizcaíno SF (2008) Paleobiology of Pleistocene ground sloths (Xenarthra, Tardigrada): biomechanics, morphogeometry and ecomorphology applied to the masticatory apparatus. Ameghiniana 45:175–196Google Scholar
  8. Bargo M, Vizcaíno SF, Kay, RF (2009) Predominance of orthal masticatory movements in the early Miocene Eucholaeops (Mammalia, Xenarthra, Tardigrada, Megalonychidae) and other megatherioid sloths. J Vertebr Paleontol 29:870–880CrossRefGoogle Scholar
  9. Blanco RE, Szerwonogora A (2003) The gait of Megatherium Cuvier 1796 (Mammalia, Xenarthra, Megatheriidae) In: Fariña RA, Vizcaíno SF, Storch G (eds) Morphological Studies in Fossil and Extant Xenarthra. Senckenb biol 83:61–68Google Scholar
  10. Canto J, Salas-Gismondi R, Cozzuol M, Yánez J (2008) The aquatic sloth Thalassocnus (Mammalia, Xenarthra) from the late Miocene of north-central Chile: biogeographic and ecological implications. J Vertebr Paleontol 28:918–922CrossRefGoogle Scholar
  11. Carlini AA, Brandoni D, Sánchez R (2006b) First megatheriines (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco (late Miocene) and Codore (Pliocene) formations, Estado Falcón, Venezuela. J Syst Palaeontol 4:269–278CrossRefGoogle Scholar
  12. Carlini AA, Scillato-Yané GJ, Sánchez R (2006a) New Mylodontoidea (Xenarthra: Phyllophaga) from the middle Miocene-Pliocene of Venezuela. J Syst Palaeontol 4:255–267CrossRefGoogle Scholar
  13. Cartelle C, Bohórquez GA (1982) Eremotherium laurillardi Lund, 1842. Parte I. Determinação específica e dimorfismo sexual. Iheringia Ser Geol (7):45–63Google Scholar
  14. Cartelle C, De Iuliis G (2006) Eremotherium laurillardi (Lund) (Xenarthra, Megatheriidae), the Panamerican giant ground sloth: taxonomic aspects of the ontogeny of skull and dentition. J Syst Palaeontol 4: 199–209CrossRefGoogle Scholar
  15. Casinos A (1996) Bipedalism and quadrupedalism in Megatherium: an attempt at biomechanical reconstruction. Lethaia 29:87–96CrossRefGoogle Scholar
  16. Chiarello AG (2008) Sloth ecology. An overview of field studies. In: Vizcaíno SF, Loughry WJ (eds) The Biology of the Xenarthra. The University of Florida Press, Gainesville, pp 269–280Google Scholar
  17. Christiansen P, Fariña RA (2003) Mass estimation of two fossil ground sloths (Mammalia, Xenarthra, Mylodontidae). In: Fariña RA, Vizcaíno SF, Storch G (eds) Morphological Studies in Fossil and Extant Xenarthra. Senckenb biol 83:95–101Google Scholar
  18. Cozzuol MA (2007) The Acre vertebrate fauna: age, diversity, and geography. J So Am Earth Sci 21:185–203CrossRefGoogle Scholar
  19. Cuvier G (1823) Sur le Megatherium. Recherches sur les ossements fossiles, 2nd édition 1:174–192Google Scholar
  20. De Iuliis G (1996) A systematic review of the Megatheriinae (Mammalia: Xenarthra: Megatheriidae). Unpublished PhD thesis. University of Toronto, Toronto, 781 ppGoogle Scholar
  21. De Iuliis G (2010) Use of anatomical features in sloth systematics. Proceedings of the 9th International Congress of Vertebrate Morphology, Punta del Este, Uruguay, July 26–31 2010 (DVD support)Google Scholar
  22. De Iuliis G, Cartelle C (1999) A new giant megatheriin ground sloth (Mammalia: Xenarthra: Megatheriidae) from the late Blancan to early Irvingtonian of Florida. Zool J Linn Soc 127:495–515CrossRefGoogle Scholar
  23. De Iuliis G, Pujos F (2006) On the systematics of Hapalops (Xenarthra: Megatherioidea). J Vertebr Paleontol 23: 55AGoogle Scholar
  24. De Iuliis G, Pujos F, Bargo MS, Toledo N, Vizcaíno SF (2009) Eucholaeops (Xenarthra, Tardigrada) remains from the Santa Cruz Formation (early Miocene), Patagonia, Argentina. Proceedings of the 10th International Mammalogical Congress, Mendoza:342AGoogle Scholar
  25. De Iuliis G, Gaudin TJ, Vicars M (2011) A new genus and species of nothrotheriid sloth (Xenarthra, Tardigrada, Nothrotheriidae) from the late Miocene (Huayquerian) of Peru. Palaeontology 54:171–205CrossRefGoogle Scholar
  26. Engelmann GF (1987) A new Deseadan sloth (Mammalia: Xenarthra) from Salla, Bolivia, and its implications for the primitive condition of the dentition in Edentates. J Vertebr Paleontol 7:217–223CrossRefGoogle Scholar
  27. Fajardo RJ, Lague MR (1999) An analysis of the morphological variation in the Santacrucian xenarthran Hapalops: implications for sloth taxonomy. Congreso Internacional Evolución Neotropical del Cenozoico, La Paz:21AGoogle Scholar
  28. Fariña RA, Blanco RE (1996) Megatherium, the stabber. Proc R Soc Lond B 263:1725–1729CrossRefGoogle Scholar
  29. Fariña RA, Vizcaíno SF, Bargo MS (1998). Body mass estimations in Lujanian (late Pleistocene - early Holocene of South America) mammal megafauna. Mastozool Neotrop 5:87–108Google Scholar
  30. Flynn JJ, Swisher CC (1995) Cenozoic South American Land mammal ages: correlation to global geochronologies. In: Berggren WA, Kent DV, Handerbol J (eds) Geochronology, Time Scales, and Correlation: Framework for a Historical Geology. SEPM Special Publication 54:317–333Google Scholar
  31. Frailey CD (1986) Late Miocene and Holocene mammals, exclusive of the Notoungulata, of the Río Acre Region, western Amazonia. Contrib Sci LA County Mus (374):1–46Google Scholar
  32. Gardner AL (2008) Mammals of South America. Volume 1, Marsupials, Xenarthrans, Shrews, and Bats. University of Chicago Press, ChicagoGoogle Scholar
  33. Gaudin TJ (2004) Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zool J Linn Soc 140:255–305CrossRefGoogle Scholar
  34. Green JL (2009) Dental microwear in the orthodentine of the Xenarthra (Mammalia) and its use in reconstructing the palaeodiet of extinct taxa: the case study of Nothrotheriops shastensis (Xenarthra, Tardigrada, Nothrotheriidae). Zool J Linn Soc 156:201–222CrossRefGoogle Scholar
  35. Hansen RM (1978) Shasta ground sloth food habits, Rampart cave, Arizona. Paleobiology 4:302–319Google Scholar
  36. Hirschfeld SE, Webb SD (1968) Plio-Pleistocene megalonychid sloths of North America. Bull Florida Mus Nat Hist 12:214–296Google Scholar
  37. Hoffstetter R (1958) Edentés Xénarthres. In: Piveteau J (ed) Traité de Paléontologie, Vol. 6(2). Masson et Cie, Paris, pp 535–636Google Scholar
  38. Hoffstetter R (1982) Les Edentés Xénarthres, un groupe singulier de la faune néotropicale (origine, affinités, radiation adaptative, migrations et extinctions). In: Montanaro Galitelli E (ed). Proceedings of the First International Meeting on “Palaeontology, Essential of Historical Geology,” Venice, pp 385–443Google Scholar
  39. Kalthoff D (2011) Microstructure of dental hard tissues in fossil and recent xenarthrans (Mammalia: Folivora and Cingulata). J Morphol 272:641–661PubMedCrossRefGoogle Scholar
  40. Lara-Ruiz P, Garcia Chiarello A (2005) Life-history traits and sexual dimorphism of the Atlantic forest maned sloth Bradypus torquatus (Xenarthra: Bradypodidae). J Zool Lond 267:63–73CrossRefGoogle Scholar
  41. MacFadden BF, DeSantis LRG, Hochstein JL, Kamenov GD (2010) Physical properties, geochemistry, and diagenesis of xenarthran teeth: prospects for interpreting the paleoecology of extinct species. Palaeogeogr Palaeoclimatol Palaeoecol 291:180–189CrossRefGoogle Scholar
  42. Martin BE (1916) Tooth development in Dasypus novemcinctus. J Morphol 27:647–691CrossRefGoogle Scholar
  43. McDonald HG (2006) Sexual dimorphism in the skull of Harlan’s ground sloth. Contrib Sci LA County Mus (510):1–9Google Scholar
  44. McDonald HG (2007) Biomechanical inferences of locomotion in ground sloths: integrating morphological and track data. In: Lucas SG, Spielmann JA, Lockley MG (eds) Cenozoic Vertebrate Tracks and Traces. New Mexico Museum of Natural History and Science Bulletin 42:201–208Google Scholar
  45. McDonald HG (2012) Evolution of the pedolateral foot in ground sloths: patterns of change in the astragalus. J Mammal Evol. doi: 10.1007/s10914-011-9182-x
  46. McDonald HG, De Iuliis G (2008) Fossil history of sloths. In: Vizcaíno SF, Loughry WJ (eds) The Biology of the Xenarthra. The University of Florida Press, Gainesville, pp 39–55Google Scholar
  47. McDonald HG, Muizon C de (2002) The cranial anatomy of Thalassocnus (Xenarthra, Mammalia), a derived nothrothere from the Neogene of the Pisco Formation (Peru). J Vertebr Paleontol 22:349–365CrossRefGoogle Scholar
  48. McKenna MC, Wyss AR, Flynn JJ (2006) Paleogene Pseudoglyptodont xenarthrans from Central Chile and Central Patagonia. Am Mus Novitates (3536):1–18Google Scholar
  49. Muizon C de, McDonald HG (1995) An aquatic sloth from the Pliocene of Peru. Nature 375:224–227CrossRefGoogle Scholar
  50. Muizon C de, McDonald HG, Salas R, Urbina M (2004) The evolution of feeding adaptations of the aquatic sloth Thalassocnus. J Vertebr Paleontol 24:398–410CrossRefGoogle Scholar
  51. Naples VL (1987) Reconstruction of cranial morphology and analysis of function in the Pleistocene ground sloth Nothrotheriops shastense (Mammalia, Megatheriidae). Contrib Sci LA County Mus (389):1–21Google Scholar
  52. Naples VL (1989) The feeding mecanism in the Pleistocene ground sloth, Glossotherium. Contrib Sci LA County Mus (425):1–23Google Scholar
  53. Nyakatura JA (2012) The convergent evolution of suspensory posture and locomotion in tree sloths. J Mammal Evol. doi: 10.1007/s10914-011-9182-x
  54. Nyakatura JA, Fischer MS (2010) Three-dimensional kinematic analysis of the pectoral girdle during upside-down locomotion of two-toed sloths (Choloepus didactylus, Linné 1758). Front Zool 7:1–16CrossRefGoogle Scholar
  55. Orr CM (2005) Knuckle-walking anteater: a convergence test of adaptation for purported knuckle-walking features of African hominidae. Am J Phys Anthropol 128:639–658PubMedCrossRefGoogle Scholar
  56. Owen R (1842) Description of the Skeleton of an Extinct Gigantic Sloth, Mylodon robustus, Owen, with Observations on the Osteology, Natural Affinities, and Probable Habits of the Megatheroid Quadrupeds in General. Direction of the Council, London, 176 pp.Google Scholar
  57. Pardiñas UF, Udrizar Sauthier DE, Carlini AA, Borrero L, Salazar-Bravo J (2008) ¿El último tardígrado de la Patagonia? In: Calvo JO, Juárez Valieri RD, Porfiri JD, dos Santos DD (eds) Actas III Congreso Latinoamericano de Paleontología de Vertebrados, Universidad Nacional de Comahue, Neuquén, pp 191AGoogle Scholar
  58. Patterson B, Pascual R (1968) Evolution of mammals on southern continents. Quart Rev Biol 43:409–451CrossRefGoogle Scholar
  59. Pujos F, De Iuliis G (2007) Late Oligocene Megatherioidea Fauna (Mammalia: Xenarthra) from Salla-Luribay (Bolivia): new data on basal sloth radiation and Cingulata-Phyllophaga split. J Vertebr Paleontol 27:132–144CrossRefGoogle Scholar
  60. Pujos F, De Iuliis G, Argot C, Werdelin L (2007) A peculiar climbing Megalonychidae from the Pleistocene of Peru and its implications for sloth history. Zool J Linn Soc 149:179–235CrossRefGoogle Scholar
  61. Pujos F, De Iuliis G, Mamani Quispe B (2011) Hiskatherium saintandrei gen. et sp. nov.: an unusual sloth from the Santacrucian of Quebrada Honda (Bolivia) and an overview of middle Miocene, small megatherioids. J Vertebr Paleontol 31(5), 1131–1149CrossRefGoogle Scholar
  62. Reid F (1997) A Field Guide to the Mammals of Central America and Southeast Mexico. Oxford University Press, OxfordGoogle Scholar
  63. Rinderknecht A, Bostelmann E, Perea D, Lecuona G (2010) A new genus and species of Mylodontidae (Mammalia: Xenarthra) from the late Miocene of southern Uruguay, with comments on the systematics of the Mylodontinae. J Vertebr Paleontol 30:899–910CrossRefGoogle Scholar
  64. Rinderknecht A, Perea D, McDonald HG (2007). A new Mylodontinae (Mammalia, Xenarthra) from the Camacho Formation (late Miocene), Uruguay. J Vertebr Paleontol 27:744–747CrossRefGoogle Scholar
  65. Shockey BJ, Salas-Gismondi R, Baby P, Guyot J-L, Baltazar MC, Huamán L, Clack A, Stucchi M, Pujos F, Emerson JM, Flynn JJ (2009) New Pleistocene cave faunas of the Andes of Central Peru: radiocarbon ages and the survival of low latitude, Pleistocene DNA. Palaeontol Electron 12:1–15Google Scholar
  66. Simpson GG (1932) Enamel on the teeth of an Eocene edentate. Bull Am Mus Nat Hist 567:1–4Google Scholar
  67. Stock C (1917) Further observations on the skull structure of mylodont sloths from Rancho La Brea. Univ Calif Publ 10:165–178Google Scholar
  68. Stock C (1925) Cenozoic gravigrade edentates of western North America. Carnegie Inst Wash Publ 331:1–206Google Scholar
  69. Vizcaíno SF (2009) The teeth of the “toothless”: novelties and key innovations in the evolution of xenarthrans (Mammalia, Xenarthra). Paleobiology 35:343–366CrossRefGoogle Scholar
  70. Vizcaíno SF, Bargo MS, Cassini GH (2006) Dental occlusal surface area in relation to body mass, food habits and other biological features in fossil xenarthrans. Ameghiniana 43:11–26Google Scholar
  71. Vizcaíno SF, Zárate M, Bargo MS, Dondas A (2001). Pleistocene burrows in the Mar del Plata area (Argentina) and their probable builders. Acta Palaeontol Pol 46:289–301Google Scholar
  72. Webb SD (1989) Osteology and relationships of Thinobadistes segnis, the first mylodont sloth in North America. In: Redford JF, Webb, SD (eds) Advances in Neotropical Mammalogy. Sandhill Crane Press, Gainesville, pp 469–532Google Scholar
  73. White JL (1993) Indicators of locomotor habits in xenarthrans: evidence for locomotor heterogeneity among fossil sloths. J Vertebr Paleontol 13:230–242CrossRefGoogle Scholar
  74. White JL (1997) Locomotor adaptations in Miocene xenarthrans. In: Kay RF, Madden RH, Cifelli RL, Flynn JJ (eds) Vertebrate Paleontology in the Neotropics: the Miocene Fauna of La Venta, Columbia. Smithsonian Institution Press, Washington, DC, pp 246–264Google Scholar
  75. White JL, MacPhee RDE (2001) The sloths of the West Indies: a systematic and phylogenetic review. In: Woods CA (ed) Biogeography of the West Indies: Patterns and Perspectives. CRC Press, New York, pp 201–235CrossRefGoogle Scholar
  76. Winge H (1941) The Interrelationships of the Mammalian Genera, vol. 1: Monotremata, Marsupialia, Insectivora, Chiroptera, Edentata. C.A. Reitzels Forlag, CopenhagenGoogle Scholar

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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