Size and Weight:
About Megatherium (Giant Sloth):
Megatherium is the poster mammal for the giant megafauna of the Pliocene and Pleistocene epochs: this prehistoric sloth was as big as an elephant, about 20 feet long from head to tail and weighing in the neighborhood of two or three tons. Fortunately for the other animals, the Giant Sloth was restricted to South America, which was cut off from other continents at the time and thus bred its own peculiar assortment of plus-sized mammals (a bit like the Australia of today).
The giant sloths of five million years ago led much different lifestyles than their modern relatives. Based on its huge, sharp claws, paleontologists believe Megatherium spent much of its time rearing up on its hind legs and ripping the leaves off trees, but some experts believe this mammal may also have been an opportunistic carnivore, slashing, killing and eating its fellow, slow-moving South American herbivores. (By the way, Megatherium was much bigger than its contemporary North American relative, Megalonyx, the first fossils of which were discovered by Thomas Jefferson.)
Megatherium is also an interesting case study in convergent evolution between dinosaurs and mammals. If you ignore the thick coat of fur, this mammal was anatomically very similar to the tall, pot-bellied, razor-clawed breed of dinosaurs known as therizinosaurs, the most imposing genus of which was the huge, feathered Therizinosaurus.