The pygmy three-toed sloth (''Bradypus pygmaeus''), also known as the monk sloth or dwarf sloth, is a

sloth Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their li ...

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

to Isla Escudo de Veraguas, a small island off the Caribbean coast of

Panama Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country spanning the southern part of North America and the northern part of South America. It is bordered by Co ...

. The species was first described by Robert P. Anderson of the

University of Kansas The University of Kansas (KU) is a public research university with its main campus in Lawrence, Kansas, United States, and several satellite campuses, research and educational centers, medical centers, and classes across the state of Kansas. Tw ...

and Charles O. Handley Jr., of the

Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...

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 The brown-throated sloth (''Bradypus variegatus'') is a species of three-toed sloth found in the Neotropical realm of Central and South America. It is the most common of the four species of three-toed sloth, and is found in the forests of South ...

. According to Anderson and Handley Jr., the head-and-body length is between , and the body mass ranges from . This sloth, like other sloths, is

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose num ...

(tree-living) and feeds on leaves. It has a body adapted to hang by its limbs; the large curved claws help the sloth to keep a strong grip on tree branches. It lives high in the canopy but descends once a week to defecate on the forest floor. It is

symbiotically Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or para ...

associated with

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( Embryophytes) have emerged deep in the Charophyte alg ...

, that can provide it with a

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

. Details of mating behavior and reproduction have not been documented. The pygmy three-toed sloth is found exclusively in the

red mangrove Red mangrove may refer to at least three plant species: * ''Rhizophora mangle'' * ''Rhizophora mucronata'' * ''Rhizophora stylosa ''Rhizophora stylosa'', the spotted mangrove, red mangrove, small stilted mangrove or stilt-root mangrove, is a tree ...

s of Isla Escudos de Veraguas, restricted to an area of . A 2012 census of pygmy three-toed sloths estimated the total population at 79. The IUCN lists the pygmy three-toed sloth as critically endangered and they are listed on

the world's 100 most threatened species The World's 100 most threatened species is a compilation of the most threatened animals, plants, and fungi in the world. It was the result of a collaboration between over 8,000 scientists from the International Union for Conservation of Nature Spe ...

Discovery and taxonomy

The pygmy three-toed sloth was first described by Robert P. Anderson of the

and Charles O. Handley Jr., of the

in 2001. The researchers noted that the

three-toed sloth The three-toed or three-fingered sloths are arboreal neotropical mammals . They are the only members of the genus ''Bradypus'' and the family Bradypodidae. The four living species of three-toed sloths are the brown-throated sloth, the maned slo ...

s found on Isla Escudo de Veraguas were significantly smaller than those that occur on the nearby outer islands of

Bocas del Toro Province Bocas del Toro (; meaning "Mouth of the Bull") is a province of Panama. Its area is 4,643.9 square kilometers, comprising the mainland and nine main islands. The province consists of the Bocas del Toro Archipelago, Bahía Almirante (Almirante ...

. Moreover, they differ from other populations in terms of

pelage Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket t ...

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

s; it gradually differentiated enough to become an independent species through

insular dwarfism Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is dist ...

. 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 Megalonychidae is an extinct family of sloths including the extinct '' Megalonyx''. Megalonychids first appeared in the early Oligocene, about 35 million years (Ma) ago, in southern Argentina (Patagonia). There is actually one possible find dati ...

Megatheriidae Megatheriidae is a family of extinct ground sloths that lived from approximately 23 mya—11,000 years ago. Megatheriids appeared during the Late Oligocene (Deseadan in the SALMA classification), some 29 million years ago, in South America. ...

and

Nothrotheriidae Nothrotheriidae is a family of extinct ground sloths that lived from approximately 17.5 mya—10,000 years ago, existing for approximately . Previously placed within the tribe Nothrotheriini or subfamily Nothrotheriinae within Megatheriidae, they ...

in the sloth superfamily Megatherioidea. The generic name ''Bradypus'' is the combination of two

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

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.

Characteristics

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 , and the body mass ranges from . 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 A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, partic ...

and shoulders forms a hood. The grayish limbs have three claws each. The tail is long. They have a relatively small and slender skull, with a large

external auditory meatus The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the pinna to the eardrum and is about in length and in diameter. Stru ...

, narrow

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

and

mandibular process The mandibular prominence is an embryological structure which gives rise to the lower portion of the face. The mandible and lower lip derive from it. The mesenchymal cells within the mandibular prominence condense to form Meckel's cartilage. It i ...

es, a minuscule

stylomastoid foramen The stylomastoid foramen is a foramen between the styloid and mastoid processes of the temporal bone of the skull. It is the termination of the facial canal, and transmits the facial nerve, and stylomastoid artery. Facial nerve inflammation in ...

, and usually lack foramina for the

external carotid artery The external carotid artery is a major artery of the head and neck. It arises from the common carotid artery when it splits into the external and internal carotid artery. External carotid artery supplies blood to the face and neck. Structure ...

and anterodorsal (meaning in front and toward the back)

nasopharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...

. The

dental formula Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolog ...

of three-toed sloths is: Two of the teeth in each jaw are

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, w ...

-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.

Distribution and status

The pygmy three-toed sloth is unique in that it is found exclusively in the

s of Isla Escudo de Veraguas; the island has a small area of approximately . A 2012 census of pygmy three-toed sloths estimated the total population at 79 – of which 70 occurred on mangroves and 9 in the surroundings. The population density was calculated as . The total area occupied by mangroves on the island was estimated to be around . While their population has presumably always been low due to their restricted range, the 2012 census found far lower numbers than had been estimated (less than 500) by the IUCN in 2010. The IUCN lists the pygmy three-toed sloth as critically endangered; it is also listed in

CITES Appendix II CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...

. According to the IUCN, conservation efforts are being hampered by conflict between local peoples and the government. Threats to the sloth's survival include timber harvesting and human settlement, that might lead to habitat degradation. After several observations, the corpses of the pygmy three-toed sloth were found to be unharmed physically, suggesting that predation is not a major threat. Instead, disease, habitat loss, or natural causes were larger factors in the species’ death. A study in 2011 showed that there were 79 pygmy sloths in the wild. Studies in 2010 and 2013 suggested a recent

population bottleneck A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Go ...

and decline in

genetic variability Genetic variability is either the presence of, or the generation of, genetic differences. It is defined as "the formation of individuals differing in genotype, or the presence of genotypically different individuals, in contrast to environmentally i ...

Ecology and behavior

The pygmy three-toed sloth, like others in its genus, is an

(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 , making it one of the slowest animals. The pygmy three-toed sloth is

related to

; 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

. 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

. A BBC documentary, in which English naturalist

Chris Packham Christopher Gary Packham CBE (born 4 May 1961) is an English naturalist, nature photographer, television presenter and author, best known for his television work including the CBBC children's nature series '' The Really Wild Show'' from 1986 ...

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 ''Cecropia'' is a Neotropical genus consisting of 61 recognized species with a highly distinctive lineage of dioecious trees. The genus consists of pioneer trees in the more or less humid parts of the Neotropics, with the majority of the speci ...

'' species eaten by brown-throated sloths on the mainland. Details of mating behavior and reproduction have not been documented.

References

External links