Smallest tree sloth

The smallest species of tree sloth alive today is the pygmy three-toed sloth Bradypus pygmaeus, which has a head-and-body length of 48–53 cm, a tail length of 4–6 cm, and a weight of 2.5–3.5 kg. Wholly restricted to Isla Escudo de Veraguas, a small remote island in the Bocas del Toro archipelago off the coast of Panama, it is also the world's rarest species of sloth, categorized as "Critically Endangered" by the IUCN, with only approximately 300 individuals thought to exist on the island, where it lives exclusively in red mangrove trees. It was not formally recognized by scientists as a valid species in its own right until 2001, following morphological and morphometic analyses, but its existence has long been known – in 1825, English illustrator Thomas Landseer produced a detailed colour engraving of one such sloth for a then in-progress work by English zoologist Edward Griffith.

Although none are known to have survived into modern times, there were once not only tree sloths but also many types of terrestrial sloths, known as ground sloths, Whereas many of these were very large, some quite enormous, on certain Caribbean islands there were a number of dwarf or pygmy species, some of which were no bigger than a domestic cat, but weighed more than the pygmy three-toed sloth.