How Slothy are Sloth Bears?
Sloth bears adapt their sleep cycle to their environment, which may be a nocturnal, diurnal, or crepuscular schedule depending on other bears, people, or predators in their habitat. Sloth bears may forage for food at night and sleep during the day to avoid potential conflicts with humans. They typically sleep 10 to 14 hours a day and do not hibernate.
Sloths, contrary to popular belief, do not sleep more than the average 10 to 12 hours, and from our last published research, we know that their activity varies depending on the individual and even differs across the same population; some sloths are more diurnal, others nocturnal.
Sloth Ranges, Then and Now
This map shows some of the important ground sloth finds in the region. Green dots represent Jefferson's ground sloth finds, and yellow triangles represent Harlan's ground sloth finds.
More information on Ground Sloths can be found at the La Brea Tarpits Web site, and at the Academy of Natural Sciences Museum.
Group of tree dwelling mammals noted for slowness
Sloths are a Neotropical group of 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 lives hanging upside down in the trees of the tropical rainforests of South America and Central America. Sloths are considered to be most closely related to anteaters, together making up the xenarthran order Pilosa.
There are six extant sloth species in two genera – Bradypus (three-toed sloths) and Choloepus (two-toed sloths). Despite this traditional naming, all sloths have three toes on each rear limb – although two-toed sloths have only two digits on each forelimb.[3] The two groups of sloths are from different, distantly related families, and are thought to have evolved their morphology via parallel evolution from terrestrial ancestors. Besides the extant species, many species of ground sloths ranging up to the size of elephants (like Megatherium) inhabited both North and South America during the Pleistocene Epoch. However, they became extinct during the Quaternary extinction event around 12,000 years ago, along with most large animals across the Americas. The extinction correlates in time with the arrival of humans, but climate change has also been suggested to have contributed. Members of an endemic radiation of Caribbean sloths also formerly lived in the Greater Antilles but became extinct after humans settled the archipelago in the mid-Holocene, around 6,000 years ago.
Sloths are so named because of their very low metabolism and deliberate movements. Sloth, related to slow, literally means "laziness", and their common names in several other languages (e.g. German: Faultier, French: paresseux, Spanish: perezoso, Romanian: leneș, Finnish: laiskiainen) also mean "lazy" or similar. Their slowness permits their low-energy diet of leaves and avoids detection by predatory hawks and cats that hunt by sight.[3] Sloths are almost helpless on the ground but are able to swim.[4] The shaggy coat has grooved hair that is host to symbiotic green algae which camouflage the animal in the trees and provide it nutrients. The algae also nourish sloth moths, some species of which exist solely on sloths.[5]
Challenges and threats
Both sloth bears and sloths have their own unique set of challenges in the wild. Sloth bears, for example, face deforestation and habitat loss. Forests are cleared for agriculture and urban settlements, resulting in sloth bears losing their home and food sources. Poachers are also an issue since sloth bears’ claws and gallbladders are sold illegally in the wildlife trade business since they are highly valued for medicine and ornamental purposes.
Sloths, both two-fingered and three-fingered, face similar challenges. In the tropical rainforests of Central and South America, rainforests are cut down for logging and converted into farmland and pastures; sloths lose both their homes and food supplies.
Both sloth bears and sloths are grappling with the impacts of human activities that threaten their survival. While each species faces unique challenges based on where and how they live, there is a common thread: most of the hurdles they encounter in the wild can be traced back to human actions.
Sloth bones and claws
All four species of ground sloth had very large claws and small, blunt teeth. They all were herbivores and probably used the teeth for browsing on trees and shrubs. The shape of their hip bones indicates that they could stand up on their hind legs. This would allow them to reach high up into trees for the best leaves and twigs.
The bone on the left is the finger bone (phalanx) that supports the claw on the thumb of a Jefferson's ground sloth. The specimen on the right is a tooth, also from a Jefferson's ground sloth.
Both of these specimens were recovered from Heinze Cave, Jefferson County, Missouri. Radiocarbon dating indicates that both specimens are more than 40,000 years old.
All four species of ground sloth became extinct in North America approximately 10,000 years ago. The reason for their extinction is being studied by paleontologists.
Taxonomy and evolution
Sloths belong to the superorder Xenarthra, a group of placental mammals believed to have evolved in the continent of South America around 60 million years ago.[6] One study found that xenarthrans broke off from other placental mammals around 100 million years ago.[7] Anteaters and armadillos are also included among Xenarthra. The earliest xenarthrans were arboreal herbivores with sturdy vertebral columns, fused pelvises, stubby teeth, and small brains. Sloths are in the taxonomic suborder Folivora[2] of the order Pilosa. These names are from the Latin 'leaf eater' and 'hairy', respectively. Pilosa is one of the smallest of the orders of the mammal class; its only other suborder contains the anteaters.
The Folivora are divided into at least eight families, only two of which have living species; the remainder are entirely extinct (†):[8]
The common ancestor of the two existing sloth genera dates to about 28 million years ago,[8] with similarities between the two- and three- toed sloths an example of convergent evolution to an arboreal lifestyle, "one of the most striking examples of convergent evolution known among mammals".[13] The ancient Xenarthra included a significantly greater variety of species, with a wider distribution, than those of today. Ancient sloths were mostly terrestrial, and some reached sizes that rival those of elephants, as was the case for Megatherium.[4]
Sloths arose in South America during a long period of isolation and eventually spread to a number of the Caribbean islands as well as North America. It is thought that swimming led to oceanic dispersal of pilosans to the Greater Antilles by the Oligocene, and that the megalonychid Pliometanastes and the mylodontid Thinobadistes were able to colonise North America about 9 million years ago, well before the formation of the Isthmus of Panama. The latter development, about 3 million years ago, allowed megatheriids and nothrotheriids to also invade North America as part of the Great American Interchange. Additionally, the nothrotheriid Thalassocnus of the west coast of South America became adapted to a semiaquatic and, eventually, perhaps fully aquatic marine lifestyle.[14] In Peru and Chile, Thalassocnus entered the coastal habitat beginning in the late Miocene. They presumably waded and paddled in the water for short period, but over a span of 4 million years, they eventually evolved into swimming creatures, becoming specialist bottom feeders of seagrasses, similar to the extant sirenians.[15]
Both types of extant tree sloth tend to occupy the same forests; in most areas, a particular species of the somewhat smaller and generally slower-moving three-toed sloth (Bradypus) and a single species of the two-toed type will jointly predominate. Based on morphological comparisons, it was thought the two-toed sloths nested phylogenetically within one of the divisions of the extinct Greater Antilles sloths.[16] Though data has been collected on over 33 different species of sloths by analyzing bone structures, many of the relationships between clades on a phylogenetic tree were unclear.[17] Much of the morphological evidence collected to support the hypothesis of diphyly has been based on the structure of the inner ear.[18]
Recently obtained molecular data from collagen[8] and mitochondrial DNA sequences[19] fall in line with the diphyly (convergent evolution) hypothesis but have overturned some of the other conclusions obtained from morphology. These investigations consistently place two-toed sloths close to mylodontids and three-toed sloths within Megatherioidea, close to Megalonyx, megatheriids and nothrotheriids. They make the previously recognized family Megalonychidae polyphyletic, with both two-toed sloths and Greater Antilles sloths being moved away from Megalonyx. Greater Antilles sloths are now placed in a separate, basal branch of the sloth evolutionary tree.[8][19]
The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data.[8]
The marine sloths of South America's Pacific coast became extinct at the end of the Pliocene following the closing of the Central American Seaway; the closing caused a cooling trend in the coastal waters which killed off much of the area's seagrass (and which would have also made thermoregulation difficult for the sloths, with their slow metabolism).[20]
Ground sloths disappeared from both North and South America shortly after the appearance of humans about 11,000 years ago. Evidence suggests human hunting contributed to the extinction of the American megafauna. Ground sloth remains found in both North and South America indicate that they were killed, cooked, and eaten by humans.[4] Climate change that came with the end of the last ice age may have also played a role, although previous similar glacial retreats were not associated with similar extinction rates.
Megalocnus and some other Caribbean sloths survived until about 5,000 years ago, long after ground sloths had died out on the mainland, but then went extinct when humans finally colonized the Greater Antilles.[21]
Are sloth bears related to sloths?
Contrary to their name, sloth bears and sloths are not closely related, and both belong to entirely different taxonomic orders and families with unique evolutionary histories. For example, sloth bears belong to the order Carnivora, which includes mammals such as dogs, cats, seals, and bears. Within this order, they are also under Ursidae or Bear family.
The name “sloth bear” comes from the bear’s slow-moving behavior and long claws, like a sloth, which led early zoologists and taxonomists to draw parallels between them. However, this similarity is due to convergent evolution, where unrelated species independently develop similar traits in response to similar environments.
Despite these surface resemblances, sloth bears and sloths are genetically and taxonomically distant as well as having strikingly different evolutionary paths.
Sloths, unlike sloth bears, belong to the order Pilosa, sharing it with anteaters and armadillos. Over millions of years, sloths have adapted to a slow-paced arboreal lifestyle, developing features like long arms, curved claws, and a slow metabolism to thrive in treetop habitats where they perform various activities, including eating, sleeping, mating, and giving birth.
What is a sloth bear?
A Sloth bear is a type of bear species native to India, Sri Lanka, Nepal, and Bhutan. Known for its long snout and long lower lip used for sucking up insects, it’s officially named Melursus ursinus. Despite the name referring to them as ‘lazy’, sloth bears are anything but lazy!
These bears have a distinctive shaggy black coat with a whitish-yellow ‘U’ or ‘Y’ shaped mark on their chest. And although they share a resemblance, sloth bears should not be confused with the Asian Black Bear (Ursus thibetanus)
Conservation Status of Sloths and Sloth Bears
IUCN is the International Union for Conservation of Nature. Under their Red List of Threatened Species, sloth bears are listed as vulnerable as of 2016 during their last assessment. Their population is decreasing, with an estimated of fewer than 20,000 individuals spread across the Indian subcontinent.
Some sloth species are in a similar situation; IUCN has the Maned Sloth listed as vulnerable with the population decreasing. Pygmy Sloths are listed as critically endangered, with a population size of around 2,000-2,500 individuals.
The Brown-Throated Sloth is listed as Least Concern, though there is evidence indicating the population is decreasing as well; for this reason, it is urgent to determine the species’ population trends.
What can we do to protect both species?
These extraordinary creatures’ continued existence hinges significantly on our actions today. This involves adopting more sustainable farming practices and endorsing conservation initiatives that safeguard the natural habitats of these animals from further degradation.
You can support organizations working with this species, like Wildlife SOS, founded in 1995; it has a strong track record in India for rescuing wildlife in distress, including sloth bears, elephants, leopards, and others. Free the Bears is an organization that works to rescue and rehabilitate bears in various Asian countries.
Four species of ground sloths inhabited the United States at the end of the last Ice Age. These were Jefferson's ground sloth (Megalonyx jeffersonii), Laurillard's ground sloth (Eremotherium laurillardi), the Shasta ground sloth (Nothrotheriops shastensis), and Harlan's ground sloth (Glossotherium harlani). Of these four only two, Jefferson's and Harlan's ground sloths, are found in the midwestern U.S.
Ground sloths were large relatives of the modern two-toed sloths (Choloepus spp.) and three-toed sloths (Bradypus spp.). Unlike modern sloths, which spend most of their time in trees, the ground sloths spent all of their time on the ground. This is fortunate because Jefferson's and Harlan's ground sloth were each about the size of an oxen.
All four species of ground sloth had very large claws. However, all were herbivores. They had relatively small, blunt teeth, which they probably used for browsing on trees and shrubs. The shape of their hip bones indicates that they could stand up on their hind legs. This would allow them to reach high up into trees for the best leaves and twigs.
The picture above shows a reconstruction of Jefferson's ground sloth from the University of Iowa Museum of Natural History.
Where do Sloth Bears Live?
Sloth Bears thrive in the Indian subcontinent’s diverse environments like dry forests, grasslands, wet forests, and mountains. They favor rocky outcrops and caves for daytime shelter. The tropical climate in these regions is marked by high temperatures and substantial rainfall, fostering a biodiverse environment.
Sloths, on the other hand, are found in the rainforests of Central and South America. Preferring a life high up in the trees where they hang using their strong claws. Sloths consider the forest canopy their primary home. They flourish in humid environments and rely on a diverse array of leaves as their main source of food.
Surprisingly, both sloth bears and sloths typically lead solitary lives. Sloth bears may be spotted in groups during times of abundant resources, and occasionally, groups of female sloths share the same tree.
