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gravigrade

Paramylodon

Paramylodon is an extinct genus of ground sloth known from North America deposits in Mexico and the United States. Currently there is just one recognized species, P. harlani, that is commonly referred to as Harlan's ground sloth in honor of American paleontologist Dr. Richard Harlan who first discovered and described a lower jaw in 1835. Paramylodon exhibits an interesting character of having had dermal ossicles, small bones embedded in the skin. This would have provided an interesting degree of protection to the animal, and this character is also shared by the South American Mylodon.

Taxonomic History

The genus was created by Brown (1903) with the species P. nebrascensis. The skull showed a number of characters similar to that of Mylodon harlani, which was also known from North America, but differed in the number of teeth present in the maxilla. Paramylodon had four teeth in the upper dentition, similar to that of Grypotherium darwini (=Mylodon darwini), but the then recognized genus of Mylodon possessed five upper teeth. P. nebrascensis was later considered to be a junior synonym of M. harlani by Stock (1925) given the large number of specimens from the La Brea Tar Pits that showed the presence of the upper caniniform to be variably lost in some specimens and retained in others. Thus the typical dental formula for the species of harlani is 5/4. Work by Kraglievich (1928) sorted through the long standing historical confusion concerning the taxonomic validity of Mylodon and Glossotherium, and determined what the type species of each genus was. An additional result was to recognize Paramylodon as generically different from Mylodon of South America and P. harlani was used as the species name as it had seniority over P. nebrascensis.

Until recently, Paramylodon was also viewed as a subspecies of Glossotherium and a number of institutions listed their specimens as Glossotherium harlani in part to work by Robertson (1976). Paramylodon is generically distinct from the South American genus of Glossotherium (see McAfee, 2007), although some question remains regarding the relationship of the late Blancan specimens that have been tentatively assigned as "Glossotherium" chapadmalense due to their seeming similarity to the South American species of the same name.

References

  • (1903): A new genus of ground sloth from the Pleistocene of Nebraska. Bulletin of the American Museum of Natural History, 19:569-583.
  • (1935): Medical and physical researches. pp. 271-275; 314-336.
  • (1928): "Mylodon Darwin" Owen, es la especie genotipo de "Mylodon" Ow. Revista de la Sociedad Argentina de Ciencias Naturales, Physis: 9(33): 169-185.
  • (2007): Reassessing the Taxonomy and Affinities of the Mylodontinae Sloths, Glossotherium and Paramylodon (Mammalia: Xenarthra: Tardigrada). Ph.D. Dissertation, Northern Illinois University. DeKalb, IL: 177pp.
  • (1976): Latest Pliestocene mammals from Haile XV A, Alachua County, Florida. Bulletin of the Florida State Museum, 20(3):111-186.
  • (1925): Cenozoic gravigrade edentates of western North America with special reference to the Pleistocene Megalonychinae and Mylodontidae of Rancho La Brea. Carnegie Institute of Washington, 331: 1-206.

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