Grazing in a New Late Oligocene Mylodontid Sloth and a Mylodontid Radiation as a Component of the Eocene-Oligocene Faunal Turnover and the Early Spread of Grasslands/Savannas in South America |
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Authors: | Bruce J Shockey Federico Anaya |
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Institution: | 1.Biology Department, Manhattan College and the Department of Vertebrate Paleontology,American Museum of Natural History,New York,USA;2.Facultad de Ingeniería Geológica,Universidad Autónoma Tomás Frías,Potosí,Bolivia |
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Abstract: | We describe a new taxon of mylodontid sloth from the late Oligocene (Deseadan South American Land Mammal “age”), Salla Beds
of Bolivia. This taxon, Paroctodontotherium calleorum, new genus and species, is one of the oldest known sloths, but it is surprisingly derived. It is referable to the Mylodontidae
and, with just a little doubt, to the Mylodontinae. It shares a number of derived characteristics with other mylodontids and
even mylodontines. These include: a relatively low temporomandibular joint; a relatively short zygomatic process of the squamosal;
an elongated, narrow braincase; anteriorly diverging toothrows; broad muzzle; and greatly enlarged external nares. The relative
width of the muzzle of Paroctodontotherium is as great as any Pleistocene mylodontid except the giant grazer, Lestodon. We review and critique methods of estimating diets of extinct sloths and propose a hypothesis in regard to the feeding ecology
of Paroctodontotherium. Based upon its broad muzzle, the degree of tooth wear, and its presence in a habitat dominated by hypsodont herbivores,
we propose that Paroctodontotherium was a bulk feeder that foraged near ground level. Grasses were likely a major component of its diet. The addition of this
new taxon, along with other recently discovered taxa, illustrates that late Oligocene sloths had much greater diversity than
recognized just a decade ago. This diversity is evident in species richness, variations in body sizes, dental morphologies,
and means of locomotion. We regard this relatively sudden sloth radiation as a significant component of the Eocene-Oligocene
faunal turnover and was related to the development of more open habitats of post-Eocene South America. |
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