Pygmy three-toed sloth

The pygmy three-toed sloth (Bradypus pygmaeus), also known as the monk sloth or dwarf sloth, is a critically endangered species of sloth in the family Bradypodidae. The species is endemic to Isla Escudo de Veraguas, a small island off the Caribbean coast of Panama. The species was first described by Robert P. Anderson of the University of Kansas and Charles O. Handley Jr., of the Smithsonian Institution in 2001. The pygmy three-toed sloth is significantly smaller than the other three members of its genus, but otherwise resembles the brown-throated three-toed sloth. According to Anderson and Handley Jr., the head-and-body length is between 48 and 53 centimetres (19 and 21 in), and the body...

The pygmy three-toed sloth, like others in its genus, is an arboreal (tree-living) animal. This sloth can spend as many as 15 to 20 hours per day on trees. It moves at an extremely slow speed of 0.24 kilometres per hour (0.15 mph), making it one of the slowest animals. The pygmy three-toed sloth is symbiotically related to green algae; a 2010 study investigated this in detail. Different sloths harbour different types of algae – only Tricophilus species were found on the brown-throated and pygmy three-toed sloths. These algae discolor the fur of the sloth, giving it a greenish hue – this serves as an efficient camouflage. Some of these algae might be transferred to offspring through the mother, others may be picked up from the surroundings over time. The smaller size of pygmy sloths reduces their energy requirements for survival and reproduction, making them an apparent example of insular dwarfism. A BBC documentary, in which English naturalist Chris Packham recognizes the pygmy three-toed sloth as the first in his list of the top ten discoveries in the 2000s, shows a rare clip of a swimming pygmy three-toed sloth. Like other sloths, the pygmy three-toed sloth feeds on leaves. It feeds on red mangrove leaves, which are relatively poor in nutrients and coarser than the tender leaves of Cecropia species eaten by brown-throated sloths on the mainland. Details of mating behavior and reproduction have not been documented.

Panama

The pygmy three-toed sloth, like others in its genus, is an arboreal (tree-living) animal. This sloth can spend as many as 15 to 20 hours per day on trees. It moves at an extremely slow speed of 0.24 kilometres per hour (0.15 mph), making it one of the slowest animals. The pygmy three-toed sloth is symbiotically related to green algae; a 2010 study investigated this in detail. Different sloths harbour different types of algae – only Tricophilus species were found on the brown-throated and pygmy three-toed sloths. These algae discolor the fur of the sloth, giving it a greenish hue – this serves as an efficient camouflage. Some of these algae might be transferred to offspring through the mother, others may be picked up from the surroundings over time. The smaller size of pygmy sloths reduces their energy requirements for survival and reproduction, making them an apparent example of insular dwarfism. A BBC documentary, in which English naturalist Chris Packham recognizes the pygmy three-toed sloth as the first in his list of the top ten discoveries in the 2000s, shows a rare clip of a swimming pygmy three-toed sloth. Like other sloths, the pygmy three-toed sloth feeds on leaves. It feeds on red mangrove leaves, which are relatively poor in nutrients and coarser than the tender leaves of Cecropia species eaten by brown-throated sloths on the mainland. Details of mating behavior and reproduction have not been documented.

The pygmy three-toed sloth is significantly smaller than the other members of its genus, but otherwise resembles the brown-throated sloth. According to Anderson and Handley Jr., the head-and-body length is between 48 and 53 centimetres (19 and 21 in), and the body mass ranges from 2.5 to 3.5 kg (5.5 to 7.7 lb). The brown-throated sloth is nearly 40% heavier and 15% smaller in head-and-body length than the pygmy three-toed sloth. Moreover, the brown-throated sloth is lighter on the crown. The face is buff to tan; a dark band runs across the brow, surrounded by an orange patch. The throat is gray to brown, lighter than the underbelly; the dark brown back is spotted and has a dark stripe along the midline. Facial hair is short, while the long, rough hair on the crown and shoulders forms a hood. The grayish limbs have three claws each. The tail is 4.5 to 6 centimetres (1.8 to 2.4 in) long. They have a relatively small and slender skull, with a large external auditory meatus, narrow squamosal and mandibular processes, a minuscule stylomastoid foramen, and usually lack foramina for the external carotid artery and anterodorsal (meaning in front and toward the back) nasopharynx. The dental formula of three-toed sloths is: 54–5 Two of the teeth in each jaw are incisor-like, although those in the upper jaw are small or may be absent. Many of the features found in pygmy sloths are thought to be indicative of a relatively rapid evolution of a new species in an isolated, island habitat. They host algae inside their fur which causes them to have a greenish color. The algae is generally more noticeable on the top of their head and neck, dorsal portions of the forelimbs, and upper backside.

The pygmy three-toed sloth was first described by Robert P. Anderson of the University of Kansas and Charles O. Handley Jr., of the Smithsonian Institution in 2001. The researchers noted that the three-toed sloths found on Isla Escudo de Veraguas were significantly smaller than those that occur on the nearby outer islands of Bocas del Toro Province. Moreover, they differ from other populations in terms of pelage and cranial characteristics. Hence, they considered the three-toed sloths in Isla Escudo de Veraguas to be an independent species and formally described it from the skin and skull of an adult female. The researchers further pointed out that Isla Escudos de Veraguas is the oldest island and located farthest from the mainland, which began breaking up into small islands due to rises in sea levels 10,000 years ago. They proposed that this species evolved from an isolated population that had originated from the mainland population of brown-throated three-toed sloths; it gradually differentiated enough to become an independent species through insular dwarfism. In another study the following year, the researchers observed that the mean body size of three-toed sloths on an island decreases linearly as the age of the island increases; the area of the island and the distance from the mainland, however, do not appear to significantly affect dwarfing. The pygmy three-toed sloth is one of the four extant members of the genus Bradypus, and is classified under the family Bradypodidae. According to molecular phylogenetic analysis, Bradypodidae nests with Megalonychidae, Megatheriidae and Nothrotheriidae in the sloth superfamily Megatherioidea. The generic name Bradypus is the combination of two Greek words: brady ("slow") and pous ("foot"). The specific name pygmaeus comes from the Greek pugmaios ("as small as a fist"). 'Monk sloth' and 'dwarf sloth' are two other names for this sloth.