Only tree-living sloths are found on the planet today, but the group was once much more diverse
Sloths have a reputation for being sluggish and slow, spending most of their lives dozing in trees, but a new study suggests this is one of the enduring secrets of their success.
Scientists have examined the evolutionary history of the animals, including extinct forms known only from the fossil records.
They say giant sloths walking the land were an easy target for the first human hunters.
In contrast, small sloths in the trees managed to cling on to survival.