Harlan's Ground Sloth

Harlan's ground sloth, Paramylodon harlani

Harlan's ground sloth is a mylodont ground sloth and one of two types of ground sloth that has been recovered from late Pleistocene sites in the Midwest. You can read about the other type, Jefferson's ground sloth, here.  Ground sloths were large relatives of the modern two-toed sloths (Choloepus spp.) and three-toed sloths (Bradypus spp.). Unlike modern sloths, which spend most of their time in trees, ground sloths spent all of their time on the ground.

For nearly two centuries there has been some controversy regarding how Harlan's ground sloth relates to other Pleistocene mylodont ground sloths, and particularly whether it belongs to the Glossotherium genus or Paramylodon genus. Consequently, Harlan's ground sloth is alternately identified as Glossotherium harlani or Paramylodon harlani within scientific literature and across the internet. This disagreement stems primarily from early confusion about how to name the different ground sloth skeletons assigned to the Mylodont family, with the result that a single species, such as Harlan's ground sloth, might have had as many as 15 different scientific names! Over time, this confusion led to disagreement about whether Paramylodon was truly a different genus than Glossotherium, with some scientists suggesting that all mylodont sloths should be assigned to the genus Glossotherium (Hoffstetter 1952; Kurtén and Anderson 1980; Simpson 1945) and others arguing that Paramylodon is a valid genus for North American mylodont sloths (Cabrera 1936; Kraglievich 1928; McDonald 1995).  A recent evaluation of physical characteristics and measurements of different mylodont species, particularly skull and jaw measurements, supports the latter argument and demonstrates that the two genera are, in fact, distinguishable from each other (McAfee 2009). For that reason, we refer to Harlan's ground sloth as P. harlani throughout this web exhibit.


Harlan's ground sloth, Paramylodon harlani

Complete Paramylodon harlani skeleton recovered from the Rancho la Brea formation in California and in the Paleobiology collections of the National Museum of Natrual History, Smithsonian Institution. Information provided with the permission of the National Museum of Natural History, Smithsonian Institution, 10th and Constitution Ave. N.W., Washington, DC 20560-0193. (https://www.nmnh.si.edu/).

Xenarthra (Sloths and Armadillos)
Mylodontidae (Mylodont ground sloths)

Length: 3 m (9.8 ft); McDonald 2005

Weight: 1100-1400 kg (2425-3085 lbs); McDonald 2005