Mass estimation in fossil sloths (Xenarthra, Folivora) from the Early ...

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than 10 kg to around 120 kg. The heavier Santacrucian genera belonged to two families, Megatheriidae and Mylodontidae, that also showed a diversity of large genera, some with gigantic body sizes, during the Plio-Pleistocene (Vizcaíno et al. 2012a). In this lights, we interpret the small body size of Choloepus as a derived condition reached independently from Bradypus. Based on the fossil evidence, the last common ancestor of the extant Choloepus and Bradypus was likely of large body size. Concluding remarks 1- The variation in body mass shown by the extant mammals analyzed in this study does not appear to be biased by phylogeny. 2- The predictive equations developed here based on several elements of the appendicular skeleton show relatively low predictive error values, especially for the scapular, humeral, femoral, and tibia-fibular equations. 3- Most Santacrucian sloths ranged between 40 and 80 kg (megalonychids and stem megatherioids), while others (megatheriids and mylodontids) ranged between 80 and 150 kg. 4- Medium and large body sizes imposed constraints on climbing capabilities of Santacrucian sloths, thus likely preventing megalonychids and stem megatherioids from accessing the finest branches, while restricting megatheriids and mylodonts largely to the ground. Acknowledgements The authors wish to thank M. Reguero and L. Pomi (MLP), W. Joyce and D. Brinkman (YPM), J. Flynn, N.B. Simmons, and C. Norris (AMNH), and W.F. Simpson and K.D. Angielczyk (FMNH) for kindly providing access to the collections under their care, and 13 13
to the Dirección de Patrimonio Cultural of Santa Cruz Province and the Museo Regional Provincial P.M.J. Molina of Río Gallegos, for support during field work. We are grateful to J.M.G. Perry for their helpful comments, and the reviewers J. White and R. Fariña for their valuable comments and suggestions that greatly improved the manuscript. This is a contribution to the projects PIP-CONICET 1054, PICT 0143, and UNLP N647, National Geographic Society to S.F. Vizcaíno and R.F. Kay, and National Science Foundation to R.F. Kay. REFERENCES Alexander R.M., Jayes S. A.G., Maloiy M.O. and Wathuta M.E. 1979. Allometry of the limb bones of mammals from shrews (Sorex) to elephant (Loxodonta). Journal of Zoology 189: 305-314. http://dx.doi.org/10.1111/j.1469-7998.1979.tb03964.x Andrews P., Lord J.M. and Evans E.M.N. 1979. Patterns of ecological diversity in fossil and modern mammalian faunas. Biological Journal of the Linnean Society, 11, 177-205. http://dx.doi.org/10.1111/j.1095-8312.1979.tb00034.x Asher R.J. and Helgen K.M. 2010. Nomenclature and placental mammal phylogeny. BMC Evolutionary Biology 10:102 http://dx.doi.org/10.1186/1471-2148-10-102 PMid:20406454 PMCid:2865478 Bargo M.S., Toledo N. and Vizcaíno S.F. 2012. Paleobiology of the Santacrucian sloths 14 14
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Page 3 and 4: INTRODUCTION The mostly fluvial dep
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Page 9 and 10: Estimated body mass of Santacrucian
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Page 36 and 37: Megatheriidae 30 MPM- PV 3408 Megat
Page 38 and 39: Table 6. Mean and weighted estimate
Page 40: 41 Inter-Condylar Femoral Width ICF

Mass estimation in fossil sloths (Xenarthra, Folivora) from the Early ...

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