Bradypodidae is the family consisting of the three-toed sloths, the one we most associate the word "sloth" with. As far as we know, they exist only in the tropical forests of Latin America and never climbed upwards to the more temperate United States.

The only sloths instead to cross the border into the United States were the few families and subfamilies of ground sloths (giants, Harlans, Shastas and Jeffersons). Being ground sloths, they did not share the three-toes' adaptations for living and instead roamed great distances for a wider variety of plant foods.

But let's say that there is a species of three-toed sloth that did make the crossing and is now munching leaves in the forests of the Appalachian Mountains. Would its lifestyle still be the same as that of its tropical cousins, or are the personalities of temperate deciduous forests so different that it would need to give its slow, arboreal, folivorous ways and be a ground sloth itself?

  • $\begingroup$ How long ago did you want your three-toed sloths to arrive in Appalachia? $\endgroup$
    – Mikey
    Mar 14 '17 at 3:50
  • $\begingroup$ Five million years. $\endgroup$ Mar 14 '17 at 4:28
  • $\begingroup$ Would moving an animal to a distinctly different environment for 50 million years change its appearance? Yes, and its species. Nearly every mammal and bird today is a different species from what we saw 50 million years ago. The three toed sloth evolved, because of its surroundings and natural selection. I thought you meant they came over like a hundred years ago. $\endgroup$
    – Mikey
    Mar 14 '17 at 4:42
  • $\begingroup$ I said five, not fifty. $\endgroup$ Mar 14 '17 at 4:51
  • $\begingroup$ Here is a video of a Canadian tree sloth. youtube.com/… $\endgroup$
    – Willk
    Mar 14 '17 at 13:40

According to the italian page on Wikipedia, sloths are unable to control their body temperature and need an environmental temperature above 22 C, therefore they are forced to live in warm tropical forests. (I could not find this info on other languages in the same source, therefore I don't fully trust it).

However their habits make sloths pretty unfit for a temperate or cold forest: standing still or sleeping 16 hours a day (so that algae start growing on your fur) can be lethal when the temperatures are far from optimal.

In addition the abundance of food is way less, therefore the reduced mobility becomes again a burden.

Your Appalachian sloths will then need to:

  • become more active in food seeking, also by moving on the ground
  • increase their methabolism
  • adapt their dietary requirements to the available food, maybe integrating leaves with insects, worms, small critters

Three toed sloths can't walk. At all. The most they can do is crawl slowly between trees and they're very vulnerable to predation while doing so.

That being said, you want them in the in the forests of the Appalachian which is a mixture of evergreens (pines and conifers) and deciduous forests.

So there's a problem right there in terms of diet.

Nothing really eats pine needles or conifer leaves, animals prefer to eat the seeds or gnaw down to the bark, neither of which the sloth is designed for.

Deciduous trees would be the better bet here, but of course they lose their leaves for a good part of the year.

The only possible way for sloths to survive through the year is to learn how to hibernate. Before that, they need to learn how to make warm nests - with their physiology, I can't see them being dextrous enough. They have a slow enough metabolism, but I'm not sure they'd be able to put on enough body weight to survive through without extra insulation (even bears can't over-winter without somewhere warm to go).

I don't really see much hope, unfortunately.


Here is your model: the Wollemi pine.


Once widespread, this ancient tree survived in just one gorge. The dawn redwood has a similar story.


So: posit a valley in the Appalachians with relict vegetation left over from before the last Ice Age - a time long ago when the climate was kind to sloths.

I like very much thinking about the explorers finding this valley that time forgot. Usually next they find prehuman ruins or dinosaurs or wizards or something of that ilk. But here: tree sloths! Cue theme from Jurassic Park.


It isn't really feasible. They would need an unbroken line of trees stretching the entire distance. Unfortunately, there are deserts and planes in the way. You can see this map of tree cover for North America:


As you can see, there are large swaths of land with few or no trees. Plus the sloths would need to cross several very wide, fast-flowing rivers. So even ignoring issues with food, there is simply no route for them to get where you want them.


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