Sloths - The rainforest’s two-toed and three-toed sloths are not closely related

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While in appearance there would seem to be little to differentiate two-toed and three-toed sloths beyond the obvious fact of their differing number of digits, morphological studies from the 1970s, supported by more recent phylogenetic data, has shown that they belong to different families. In other words, they are not closely related and their ancestors took to the trees independently of one another.

Three-toed sloths are around the size of a small domestic dog. They can weigh between 3.5 and 4.5 kilograms, and be up to 45 centimeters in length. In addition to the three claws on each of their four limbs, they can also be distinguished by their tails.

There are four species of three-toed sloth, of which B. variegatus (the “brown-throated three-toed sloth”) is found in Peru. They live their entire lives in the trees, except when they need to defecate; they descend from the high canopy once a week in order to relieve themselves on the rainforest floor. They tend to move between trees around four times a day, with individuals endeavoring to stick to their own territory and not encroach upon other sloths’ ranges. While they are certainly as slow as their name suggests when moving through the forest, three-toed sloths are in fact extremely able swimmers, unlike two-toed sloths. Female three-toed sloths give birth to a single young six months after mating. Females will emit screams that can be heard across the rainforest when they are ready to mate. On average, sloth copulation lasts around 25 minutes.

The two species of two-toed sloths found in the Americas, including Peru, are Choloepus didactylus (Linnaeus’s two-toed sloth) and Choloepus hoffmanni (Hoffmann’s two-toed sloth). While the former’s range is limited to South America’s Amazon basin, the latter is also found in Central America. Two-toed sloths are larger than three-toed sloths and tend to move faster. In fact, the name “two-toed sloth” is slightly misleading; they have two fingers on their front limbs, and three toes on their hind limbs. A more accurate name would be “two-fingered sloth”. Two-toed sloths weigh in at around 4 to 8 kilograms and grow up to 70 centimeters in length. They also have longer fur and are tailless.

In addition to their leaf-based diet, what all sloths share is the reason for their slowness; while different species possess differing numbers of vertebra, they all have long arms combined with the small, narrow shoulder blades which restrict their movement. To conserve energy, they hang upside down in the rainforest canopy, rather than having to balance, and they can sleep for up to 18 hours a day. Sloths’ slow movements can also prove life saving: predators often fail to spot them among the branches.