Paramylodon - Harlan’s Ground Sloth
Mounted specimen on display at the Page Museum, Los Angeles, California, USA.
When: late Pliocene to Pleistocene (~5 million to 11,000 years ago)
Where: Central and North America
What: Paramylodon is the most common of the ground sloths found at the La Brea tar pits fossil site in southern California. Megalonyx is found here as well, and though the two sloths resemble one another very strongly, they are on opposite sides of the family tree of sloths. Megalonyx is very closely related to the living two-toed sloth, but Paramylodon and its kin form a group at the base of sloths with no living relatives. The last common ancestor of these sloths lived roughly 30 million years ago. A suite of detailed morphological features distinguish these two sloths, found thoughout the skeleton, but perhaps the most amazing is that Paramylodon was somewhat of an armored animal. Imbedded within its skin were many tiny dermal ossicals, which would have served to protect it from the many predators that roamed southern California at the time.
The most complete specimens of Paramylodon come from the La Brea tar pits (which is a very redundant name as la brea means the tar, but hey!). The tar formed tens of thousands of years ago, by natural seepage of the sticky and dense material from the bedrock. The tar pits looked nothing like they do today, however. There were no large ‘lakes’ of tar then. Instead what would occur is occasionally a large seepage would collect and then be covered by leaves and dirt, hiding it from view. This would create a natural trap that would ensnare whichever animal was unfortunate enough to stumble upon it. The large expanses of tar visible today are due to the excavation of the site. The site was recognized as fossil bearing in the early 1900s, bones had been discovered on Rancho La Brea for some time previous to this, but they had not been properly identified as fossils. The Page Museum was opened on the site in 1977 in order to provide both a place for researchers to easily access and study the specimens, and to display the wondrous finds to the people of Los Angeles.