Two-Toed vs Three-Toed Sloth: Key Differences Explained

Key differences at a glance

Although they look alike and live in the same forests, two-toed and three-toed sloths are not close relatives. They belong to two separate families whose common ancestor lived roughly 30 million years ago. Their shared upside-down lifestyle is one of the most striking examples of convergent evolution in mammals: two lineages arriving at the same body plan independently.

There are two living two-toed sloths, Hoffmann’s two-toed sloth and Linnaeus’s two-toed sloth, in the genus Choloepus. There are four three-toed sloths in the genus Bradypus: the brown-throated sloth, the pale-throated sloth, the maned sloth and the pygmy three-toed sloth.

Fingers, not toes

The names are a little misleading. All sloths have three clawed toes on the hind feet. The difference is in the “hands”: two-toed sloths have two long claws on each front foot, three-toed sloths have three. For this reason, many zoologists prefer the names two-fingered and three-fingered sloth.

The claws themselves are similar: long, curved hooks of about 5–10 cm (2–4 in) that let sloths hang from branches with little effort. In three-toed sloths, the front claws are closely joined, while in two-toed sloths the two fingers are more clearly separate.

Face, fur and color

The faces are the quickest clue from a distance:

• Two-toed sloths have a pale, rather plain face with a longer, naked, pig-like snout and no strong markings. The fur is long, shaggy and tan to light brown, often paler on the head.
• Three-toed sloths have a round, flat face with dark stripes running back from the eyes, giving them a masked, smiling look. Their fur is grayish-brown, and in the brown-throated sloth the throat and forehead are darker.

Adult male three-toed sloths also have a speculum, a patch of short orange or yellow fur with a dark stripe between the shoulders. Two-toed sloths have no such patch. Both groups often look greenish because algae grow in their hair.

Three-toed sloths have a short but visible tail of a few centimeters; two-toed sloths have only a tiny stub hidden in the fur.

Which is bigger?

Two-toed sloths are the heavyweights. Most adult Hoffmann’s two-toed sloths weigh 4–8 kg (9–18 lb), with a head-and-body length of about 54–72 cm (21–28 in). Brown-throated three-toed sloths usually weigh 2.25–6.3 kg (5–14 lb) and measure about 42–80 cm (17–31 in) in total, including the tail. The smallest of all is the pygmy three-toed sloth, found only on Isla Escudo de Veraguas off Panama, which is noticeably smaller than its mainland relatives. Island animals often shrink over many generations, and this sloth is a classic example.

Remember that a sloth’s weight changes from day to day. A big share of it is fermenting leaves in the stomach, plus droppings and urine stored for several days before the next trip to the ground.

The neck: a record-breaking skeleton

Almost all mammals, from mice to giraffes, have seven neck vertebrae. Sloths are among the very few exceptions, and the two groups break the rule in opposite directions.

Three-toed sloths have eight or nine neck vertebrae. Their flexible necks let them turn their heads up to about 270 degrees, so they can scan for leaves without moving their bodies. Two-toed sloths usually have five to seven, and the number can vary between individuals. Manatees, with six, are the only other well-known exception.

Diet and daily rhythm

Three-toed sloths are leaf specialists. They eat young leaves, buds and shoots from a fairly small set of trees, often the same ones their mothers used. Two-toed sloths eat leaves too, but also more fruit, flowers and shoots, and they have been recorded at mineral licks. There are occasional reports of them taking animal food. The details are in what do sloths eat?.

Activity differs as well. Two-toed sloths are mostly nocturnal, sleeping by day in tangles of vines and moving for several hours at night. Three-toed sloths are active in short bouts both day and night, which is why they are the ones most visitors see moving in daylight.

Behavior and temper

Both are solitary, slow and quiet, and both rely on stillness and camouflage to avoid predators such as harpy eagles and jaguars. Two-toed sloths, however, have sharp, canine-like front teeth and are more likely to bite and swipe when disturbed. Three-toed sloths have only simple peg-like teeth and tend to be calmer, though they can still hurt you with their claws. Either way, wild sloths should never be handled.

Both come to the ground roughly once a week to defecate and both can swim well; see can sloths swim?.

Where they live and how long they live

The ranges overlap widely. In Central America, Hoffmann’s two-toed sloth and the brown-throated three-toed sloth often share the same forest, from Honduras and Nicaragua to Panama. In South America, the two groups live side by side in much of the Amazon, while the maned three-toed sloth is found only in Brazil’s Atlantic Forest.

Wild lifespans are poorly known for both. Three-toed sloths are estimated to live about 20 to 30 years in the wild. Two-toed sloths do very well in zoos, often living 20 to 30 years and sometimes over 40, while three-toed sloths rarely survive long in captivity because of their specialized diet. More in how long do sloths live?.

Can they interbreed?

No. Two-toed and three-toed sloths belong to different families and separated tens of millions of years ago. They cannot produce hybrids, even when they share a tree. In terms of ancestry, two-toed sloths are actually closer to some extinct giant ground sloths than they are to three-toed sloths.

Their conservation outlook differs too. Both two-toed sloths are listed as Least Concern by the IUCN, as are the brown-throated and pale-throated three-toed sloths. The maned three-toed sloth of Brazil’s Atlantic Forest is Vulnerable, and the pygmy three-toed sloth is Critically Endangered, with a tiny population confined to mangroves on one island. All sloths suffer from forest loss, power lines, roads, dogs and capture for the pet and tourist-photo trade.