The term “sloth” is English is usually not considered to be complimentary. One of the first Europeans to encounter a sloth in South America, the Spanish explorer Gonzalo Fernandez de Oviedo y Valdes, is reported to have written:
“I have never seen anything uglier or more useless than the sloth.”
Sloths, armadillos, and anteaters all belong to the order Xenartha. Ian Lange, in his book Ice Age Mammals of North America, reports:
“The order Xenartha contains some of the largest and most bizarre animals of the Pleistocene epoch—or of any age for that matter.”
The ancestors of these animals, according to the fossil record, date back to about 55 million years ago in South America.
One of the most famous fossil sites in the world, Rancho La Brea (commonly known as the La Brea Tar Pits) in Los Angeles has a number of examples of ancient sloth fossils.
Harlan’s Ground Sloth
Harlan’s Ground Sloth (Glossotherium harlani) is a medium-sized ground sloth. It stood over six feet tall and weighed about 1,500 pounds. Harlan’s Ground Sloth had small nodules of bone, known as osteoderms, buried in its skin which provided a kind of armor against attack by predators. The ground sloth is related to present-day armadillos as well as the small tree sloths of Central and South America.
In his book Ice Age Mammals of North America, Ian Lange reports:
“The construction of the skull shows a small brain cavity and a good nose for smelling. What it lacked in brain power, it made up for in bulk. When mature, Harlan’s ground sloths had essentially no enemies except humans.”
At Rancho La Brea, the youngest remains of this animal date to about 13,890 years ago. There is some indication, however, that it may have survived in Florida after it became extinct in California.
Harlan’s Ground Sloth ranged across the southern portion of what is now the United States and fossils have been found as far north as Washington. Fossils have been found in at least 40 sites and at Rancho La Brea the remains of 76 individuals have been found.
Shasta Ground Sloth
The Shasta Ground Sloth (Nothrotheriops shastense) was a small ground sloth with a tubular-shaped snout and fewer teeth than the larger sloths. It fed on the leaves of shrubs or low-hanging branches. Ian Lange reports:
“Likely the smallest of the now-extinct North American sloths, a full-grown Shasta measured up to 9 feet (3 meters) long and weighed between 300 and 400 pounds (135 and 180 kilograms).”
The Shasta ground sloth walked on it knuckles. Among the evidence of the Shasta Ground Sloth are coprolites (fossilized dung) from Rampart Cave in northwestern Arizona. Samples from this cave have been dated to 40,000 and 11,000 years before present.
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