Sloth Relatives Part One: Living Relatives

The word “sloth” refers to two different, but similar, groups of animals: Two-toed sloths (genus Choloepus), and Three-toed sloths (genus Bradypus).

Actually, they both have three toes (on their back legs), but the “two-toed” sloths have only two fingers on their fore-limbs, while the “three-toed” have three fingers on their fore-limbs.

Three-toed sloth at the Dallas World Aquarium, photo by Sergio Delgado

Two-toed sloth in Costa Rica, photo by Stevenj/Leyo

Bradypus and Choloepus sloths are actually only distant relatives, in the same way that cats and dogs are related.  Bradypus sloths are in the Family Bradypodidae, and Choloepus sloths are in the Family Megalonychidae.

In case you need a refresher, basic scientific classification works in this hierarchy from the top down:  Kingdom, Phylum, Class, Order, Family, Genus, Species.  To get fancy, we can break it up even more:  Kingdom, Phylum, Subphylum, Class, Subclass, Infraclass, Order, Suborder, Superfamily, Family, Genus, Species.

So many possibilities!  

Humans and sloths match all the way down through “Infraclass,” like this:  
Kingdom:  Animalia
Phylum: Chordata
Subphylum: Vertebrara
Class: Mammalia
Subclass: Theria
Infraclass: Eutheria

But when we get to Order, humans are Primates, and sloths are Pilosa.  As Primates, humans are more closely related to other primates such as chimpanzees, gorillas, monkeys, and lemurs.  As Pilosa, sloths are more closely related to anteaters.

Hmm, this Northern Tamandua anteater looks vaguely similar to the Costa Rican sloths in the neighborhood.   Photo by Dirk van der Made

At the SuperOrder level, sloths are Xenarthra, making them related to armadillos, but a little less closely than to the anteaters.

Nine-banded armadillo in Florida, not as fuzzy!  Photo by www.bird photos.com.

Keep in mind that humans are always learning more and more things about animals and plants, so they keep having to change their classifications to match as they get a more refined understanding. The most important thing to know is that sloths are awesome!