Three-toed or two-toed? The Different Types of Sloths

As a sloth lover, we are sure you see lots of pictures of sloths. While basically all of the pictures of sloths are amazing because the sloths are so cute and interesting, you have probably seen that some sloths look very different from others. This might bring about some questions?

“What are the different species of sloths?”
“How are those species different?”

We’re going to spend some time discussing those different species so that you can become the sloth expert you really want to be.

Two-toes or three?

So, generally scientist designate 6 different species of sloths divided into 2 different varieties:

Three-toed Sloths:

  • Maned sloth (Bradypus torquatus)
  • Pale-throated sloth (Bradypus tridactylus)
  • Brown-throated sloth (Bradypus variegatus)
  • Pygmy three-toed sloth (Bradypus pygmaeus)

Two-toed Sloths:

  • Linnaeus’s two-toed sloth (Choloepus didactylus)
  • Hoffman’s two-toed sloth (Choloepus hoffmanni)


All the Sloths!

There are some things that all sloths share. All sloths are adorable, of course, but beyond that we know that all sloths come from the same clade (a group of animals descended from the same ancient ancestor).  The clade that sloths are part of is Xenartha, which also includes some other “strange” animals such as armadillos and anteaters.

Original: cliff1066™ / CC BY (https://creativecommons.org/licenses/by/3.0)


Malene Thyssen / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)


Specifically, sloths are part of the suborder the Folivora. Both types of sloth live in the tropical rainforests of Latin America (no sloths are found in the wild in any other part of the world). Their habitat is more specifically in the trees where both types of sloths feed almost exclusively on leaves, though fruit is sometimes part of their diet and even some carnivorous habits have been observed. 

Most species of sloth are about the same size, though there is some variance, and they all have bodies adapted for their tree-bound lifestyle. The interesting thing though is that three-toed sloths and two-toed sloths are actually pretty distant cousins. So, while prehistoric sloths lived on the ground, it wasn’t that eventually one variety of sloth became adapted to living in trees and modern sloths evolved from that one ancient tree sloth. What actually happened so totally different lines of ancient sloth adapted to live in trees and overtime those sloths became more and more like each other.  This is known as convergent evolution and it’s a rare and remarkable event in evolutionary biology.

However, despite having evolved similarly, the two types of sloths to have important differences.

Three-Toed Sloths

The three-toed sloths are designated as part of the Bradypodidae family and of the genus Bradypus. They are different from the two-toed sloths not only because of the number of toes, but other physical aspects as well. Namely, the three-toed sloths have shorter hair, especially on their face, and a shorter snout, which gives them more of an appearance of having a human-like head with a nose and a mouth, which often looks like it’s smiling. 

Another physical difference is that three-toed sloths have extra vertebrae in their spine. This is strange because almost all mammals only have 7 vertebrae. This difference allows them to turn their heads almost completely around, like this guy here:

Males and female sloths look different in most three-toed sloth species (the maned sloth being the exception), with the males having a colored patch on their back: 

https://slothconservation.com/male-sloth-speculum/

Three-toed sloths are the slower of the two varieties, and they may sometimes spend an entire day without moving. This might seem like a disadvantage, but scientists have observed that sloth predators prey on two-toed sloths more often than their three-toed cousins. Thus, that slowness actually protects the three-toed sloths. (See our article: Why Are Sloths So Slow? How Slow Are Sloths?)

Three-toed sloths’ diets are somewhat more particular eaters. They almost only eat the leaves of the cecropia tree. This probably is the reason why they are even more docile than their two-toed sloths.

Reproduction is one of the main ways in which three-toed sloths are distinct from their cousins. Three-toed sloths only mate during August and September and they generally only mate with one other sloth during that time. Two-toed sloths, as we will learn, are a bit more libertine.

Two-Toed Sloths

The two species of two-toed sloths are part of the family Megalonychidae and the genus Choloepus, a totally distinct family and genus from the three-toed sloth. The Hoffman’s two-toed sloth has a light colored throat. The Linnaeus’s two-toed sloth has a darker color fur on its throat.

The fur of two-toed sloth is different from their three-toed cousins in that the Hoffman’s and Linnaeus’s sloth have longer hair, especially around the abdomen. Also, on a near microscopic level the two-toed sloths have long grooves along their hair, which is different from the fur on the three-toed sloth that have tiny transverse sloths. This can lead to the three-toed sloths having more green algae in their fur. 

Sex and reproduction are very different for the two-toed sloths. The sex ratio of the population is very different. There are 11 females born for every male. This means that in order for everyone to have a chance to reproduce the males mate with multiple females. However, females also tend to mate with multiple males. Furthermore, rather than only hooking up during a specific mating season, two-toed sloths are always down to fornicate any time of the year. 

That might sound like fun, but it balances out. While the three-toed sloths have a pregnancy period of only 6 months (compared to 9 months for humans), two-toed sloths have a pregnancy that lasts an entire year!

Range of Sloth Species

Brown-throated three-toed sloth (B. variegatus): Honduras to northern Argentina; 

Pale-throated three-toed sloth (B. tridactylus): northern South America; 

Maned sloth (B. torquatus): southeastern Brazil; 

Pygmy three-toed sloth (B. pygmaeus): Isla Escudo de Veraguas, in Panama

Linnaeus’s two-toed sloth (C. didactylus): the Amazon basin. 

Hoffmann’s two-toed sloth (C. hoffmanni):  from Honduras to the northern coast of South America, and separately in the western part of the Amazon rainforest.

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