Giant Ice Age ground sloths once roamed the wilds of the prehistoric Americas and are decendants of the much smaller tree sloths of the modern era. One of the larger of these slow-moving ground sloths, Megalonyx jeffersonii ("Great claw"), reached nearly 10 feet in height and would intimidate any ancient human hunter. Credit: Dr. Nicolás R. Chimento et al. Megatherium is just one of a number of giant ground sloths species that thrived in South America from the Early Pliocene epoch 5 million years ago through the end of the Pleistocene epoch some 11,700 years ago. Scientists have determined that the earliest and tiniest known species of the genus is Megatherium altiplanicum from Bolivia's Pliocene epoch.