Sloths once lived both on the ground and in trees, but ground sloths, too slow to outmaeuver enemies, are now extinct, leaving only the familiar upside-down tree dwelling variety.* The surviving species belong to families Megalonychidae (two toed sloths) and Bradypodidae (three toed sloths); only one species (Bradypus torquatus) is currently listed as endangered, though the deforestation of South America’s rainforests may spell trouble for the rest as well.
These animals are slow moving, low in muscle mass for their size, and the stomach of well-fed adult can make up 2/3 of it’s body weight. They are not, in other words, so very different from many of the grad students at major universities, who have likewise adapted coping mechanisms (including slow progress and binge eating) to compensate for their diminishing habitat, and for the scarceness and unpalatable nature of available resources, (particularly once they have remained in their doctoral programs past normative time). **
*Until the arrival of humans on the North and South American continents, they were poplulated with ground sloths, now extinct. Human hunting of these slow-moving targets likely had a large part in their extinction, though the concommitant Ice age probably helped.