Although two-fingered and three-fingered sloths look and act similar they are not closely related to each other. Instead, they are examples of convergent evolution, which is when two different animals evolve similar traits to adapt to the same niche in an ecosystem.
Every aspect of both two- and three-fingered sloth biology is adapted to the common goal of saving energy.
3.1 Two-fingered sloths
There are two living species of two-fingered sloth, thought to have diverged 6-7 million years ago.
- Two-fingered sloths are much larger than their three-fingered counterparts, reaching 80cm in length and weighing up to 11 Kg (although the average is 4-8 Kg).
- They have a long, pig-like snout and can sweat only from the very tip of their nose. Like humans, they sweat when they are hot or stressed.
- Their hands and feet have fleshy, hairless palms and soles.
- They have long, brown hair which is lighter in coloration around the face, and can stand on end when threatened, helping to make the sloth appear larger.
- Just like human hair, sloth hair comes in lots of different colors. Two-fingered sloths living in the hot lowland forests tend to have blonde hair, while those sloths living at higher altitudes typically have darker and thicker fur to cope with the colder climate. You can sometimes even see ginger sloths!
- Two-fingered sloths are more active and generally faster-moving than three-fingered sloths. For a long time, it was thought that their activity was primarily nocturnal, but scientists are now learning that diurnal movements are also common in these species.
- Two-fingered sloths have 46 ribs, more than any other mammal! For comparison, humans have 24 ribs, and whales only have 18. These extra ribs help support their stomach when hanging upside down, and are very flexible, making them hard to break. Sloths have been known to survive falls from nearly 30 meters (90 feet) up in the rainforest canopy.
Hoffmann’s sloth (Choloepus hoffmanni)
- Conservation status: Least concern
The Hoffmann’s two-fingered sloth can be found inhabiting tropical forests ranging from sea level up to an elevation of 3000 meters (9800 feet, or 1.8 miles).
There are two separate populations of C. hoffmanni on either side of the Andes mountain range. The most northern population ranges from eastern Honduras to western Ecuador, and the southern population ranges from eastern Peru to western Brazil and northern Bolivia.
These two populations are thought to have diverged up to 7 million years ago. There are 5 suggested subspecies.
Linnaeus’s sloth (Choloepus didactylus)
- Conservation status: Least concern
The Linnaeus’s two-fingered sloth is of similar appearance to C. hoffmanni, but has much darker coloration on the snout, hands, and feet.
This species ranges from Venezuela, the Guyanas, and Colombia to Ecuador, Peru, and Brazil north of the Amazon River. There is some evidence to suggest that they also extend into Bolivia.
This species of sloth is frequently maintained in zoological institutions worldwide due to the ease at which individuals can be exported from countries within its home range.
3.2 Three-fingered sloths
There are 4 living species of three-fingered sloths, all of which live within the forests of Central and South America where the tropical climate maintains relatively warm temperatures all year round.
The 4 species include:
- Brown-throated sloth (Bradypus variegatus)
- Pygmy sloth (Bradypus pygmaeus)
- Pale throated sloth (Bradypus tridactylus)
- Maned sloth (Bradypus torquatus)
