In today's North and South America, there is a group of sloths as big as cats living in trees. They hang on branches all day long, move slowly and rarely, and are known as the "laziest beasts". It's hard to imagine that just 10,000 years ago, their cousins, 500 times larger than them, weighed 4 to 5 tons, and were still wandering the wilderness of South America.
Both earth sloths and sloths belong to the order Phiphi suborder Pycnogena. Most of these extinct sloths live on the ground, hence the name sloth, not sloth. There are many types of ground sloths, varying in size, but their appearance and habits are somewhat similar. The earth sloth is the largest and most famous animal, the third largest land animal in the Ice Age Americas, after mammoths and mastodons.
Compared to its larger body, the ground sloth has a smaller head and a snout that extends forward, which makes it easier to feed on plants. It is also certain that they have a long tongue sticking out of their mouths and rolling up branches and leaves. From the preserved tissue of the corpse, we know that the earth sloth was covered with long, thick hairs, and under its skin there were many hard boils like small bones. These hard furs are formed by the keratinization of the inner skin, and although they are not as hard as the scales of armadillos and pangolins, they remain an unbreakable protective layer in adulthood. This, combined with their large bodies and strong physical strength, makes up for the fact that their bodies are dull and heavy.
It is unbelievable that such a heavy beast can walk upright on its hind legs. To accommodate this mode of movement, they have a well-developed torso and hindlimbs that are significantly thicker than their forelimbs, but even so, they are under a lot of pressure when they stand upright. What's more, the huge claws 40 cm long on the three inner toes of the forelimbs and the huge claws on the hind limbs make it impossible for them to land on all fours or on both feet. They can only walk sideways like large anteaters, and ground sloths weigh 100 times more than large anteaters. Fossil footprints of earth sloths have been found, in the shape of commas, suggesting that they did land on the side of their feet.
Ground sloths are generally considered vegetarians, feeding mainly on leaves and therefore relying more on a stable environment than grinders. But recent studies of their bones and claws have shown that they occasionally make cameo predators, injuring prey with their massive claws and squeezing them to death with their powerful forearms. More often, it may be eating carrion or getting food from other predators. In the BBC's popular science film Walking with the Ancients, there is a scene in which a land lazily robs a group of chaotic blade-toothed tigers of prey, and even slaps an adult tiger to try to stop it. So sloths aren't good bullies either.