54-546: See text 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, however, one possible find dating to the Eocene , about 40 Ma ago, on Seymour Island in Antarctica (which was then still connected to South America). They first reached North America by island-hopping across
108-435: 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
162-514: A 2000 article by Harington et al. in Arctic claimed that "nearly every good specimen has been described as a different species". A broader perspective on the group, accounting for age, sex, individual and geographic differences, indicates that only three species are valid ( M. leptostomus , M. wheatleyi , and M. jeffersonii ) in the late Pliocene and Pleistocene of North America. Although work by McDonald lists five species. Jefferson's ground sloth has
216-572: A day. Two-toed sloths are nocturnal . Three-toed sloths are mostly nocturnal but can be active in the day. They spend 90 per cent of their time motionless. Sloths are solitary animals that rarely interact with one another except during breeding season, though female sloths do sometimes congregate, more so than do males. Sloths descend about once every eight days to defecate on the ground. The reason and mechanism behind this behavior have long been debated among scientists. There are at least five hypotheses: 1) fertilize trees when feces are deposited at
270-418: A fall indirectly because the mothers prove unwilling to leave the safety of the trees to retrieve the young. Females normally bear one baby every year, but sometimes sloths' low level of movement actually keeps females from finding males for longer than one year. Sloths are not particularly sexually dimorphic and several zoos have received sloths of the wrong sex. The average lifespan of two-toed sloths in
324-572: A highly specific community of commensal beetles , mites and moths . The species of sloths recorded to host arthropods include the pale-throated three-toed sloth, the brown-throated three-toed sloth, and Linnaeus's two-toed sloth. Sloths benefit from their relationship with moths because the moths are responsible for fertilizing algae on the sloth, which provides them with nutrients. Their limbs are adapted for hanging and grasping, not for supporting their weight. Muscle mass makes up only 25 to 30 percent of their total body weight. Most other mammals have
378-472: A marginally higher speed of 4.5 m (15 ft) per minute if they are in immediate danger from a predator. While they sometimes sit on top of branches, they usually eat, sleep, and even give birth hanging from branches. They sometimes remain hanging from branches even after death. On the ground, the maximum speed of sloths is 3 m (9.8 ft) per minute. Two-toed sloths are generally better able than three-toed sloths to disperse between clumps of trees on
432-490: A muscle mass that makes up 40 to 45 percent of their total body weight. Their specialised hands and feet have long, curved claws to allow them to hang upside down from branches without effort, and are used to drag themselves along the ground, since they cannot walk. On three-toed sloths, the arms are 50 percent longer than the legs. Sloths move only when necessary and even then, very slowly. They usually move at an average speed of 4 m (13 ft) per minute but can move at
486-416: 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 . 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. Much of
540-675: A special place in modern paleontology , for Thomas Jefferson 's "memoir" on Megalonyx , read before the American Philosophical Society of Philadelphia , on 10 March 1797, marked the beginning of vertebrate paleontology in North America. Jefferson's paper was published, with an accompanying description and illustrations of the Megalonyx fossils by Casper Wistar , in 1799. When Lewis and Clark set out, Jefferson instructed Meriwether Lewis to keep an eye out for ground sloths. He
594-625: A tree, they are held in place by the claws themselves and often do not fall down even if shot from below. Sloths are victims of animal trafficking where they are sold as pets. However, they generally make very poor pets, as they have such a specialized ecology. The Sloth Institute Costa Rica is known for caring, rehabilitating and releasing sloths back into the wild. Also in Costa Rica, the Aviarios Sloth Sanctuary cares for sloths. It has rehabilitated and returned about 130 individuals to
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#1732876647938648-497: Is based on collagen and mitochondrial DNA sequence data (see Fig. 4 of Presslee et al ., 2019). Neocnus dousman Acratocnus ye Neocnus comes Parocnus serus Scelidotheriidae Mylodontidae Choloepodidae (two-toed sloths) Megalonychidae Bradypodidae (three-toed sloths) Nothrotheriidae Megatheriidae Sloths in the Caribbean survived about 5,000 years longer than ground sloths on
702-565: The Aves Ridge is suggested to have formed a land bridge during the interval, allowing overland migration into the Greater Antilles. The existence of such a land bridge has been questioned because of the lack of geological evidence for the Aves Ridge having been subaerially exposed as well as the fact that many other South American animals (such as marsupials and ungulates ) are absent from
756-665: The Central American Seaway , about 9 million years ago, prior to formation of the Isthmus of Panama about 2.7 million years ago (which led to the main pulse of the Great American Interchange ). Some megalonychid lineages increased in size as time passed. The first species of these were small and may have been partly tree-dwelling, whereas the Pliocene (about 5 to 2 million years ago) species were already approximately half
810-771: The Early Oligocene to the Mid- Holocene . They are known from Cuba , Hispaniola and Puerto Rico , but are absent from Jamaica . While they were formerly placed in the Megalonychidae alongside two-toed sloths and ground sloths like Megalonyx , recent mitochondrial DNA and collagen sequencing studies place them as the earliest diverging group basal to all other sloths. or as an outgroup to Megatherioidea . They displayed significant diversity in body size and lifestyle, with Megalocnus being terrestrial and probably weighing several hundred kilograms, while Neocnus
864-683: 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. Sloths are almost helpless on
918-558: The Quaternary extinction event following the arrival of humans to the Americas. Megalonyx , which means "giant claw", is a widespread North American genus that lived past the close of the last (Wisconsin) glaciation , when so many large mammals died out. Remains have been found as far north as Alaska and the Yukon . Ongoing excavations at Tarkio Valley in southwest Iowa may reveal something of
972-757: The biomass of arboreal mammals. Four of the six living species are currently rated "least concern"; the maned three-toed sloth ( Bradypus torquatus ), which inhabits Brazil's dwindling Atlantic Forest , is classified as "vulnerable", while the island-dwelling pygmy three-toed sloth ( B. pygmaeus ) is critically endangered . Sloths' lower metabolism confines them to the tropics, and they adopt thermoregulation behaviors of cold-blooded animals such as sunning themselves. The majority of recorded sloth deaths in Costa Rica are due to contact with electrical lines and poachers . Their claws also provide another, unexpected deterrent to human hunters; when hanging upside-down in
1026-467: The manatees , with six. Sloths have colour vision but have poor visual acuity. They also have poor hearing. Thus, they rely on their sense of smell and touch to find food. Sloths have very low metabolic rates (less than half of that expected for a mammal of their size), and low body temperatures: 30 to 34 °C (86 to 93 °F) when active, and still lower when resting. Sloths are heterothermic , meaning their body temperature may vary according to
1080-703: The Greater Antilles, making a complete land bridge unlikely. The earliest evidence suggesting the presence of sloths in the Caribbean is a partial femur from the Early Oligocene of Puerto Rico . Other pre-Pleistocene fossil remains include Imagocnus from the Early Miocene of Cuba , and an indeterminate species from the Late Miocene of the Dominican Republic. Megalocnid sloths were relatively small compared to mainland ground sloths, though they were
1134-451: The Oligocene, suggesting an early radiation within the group. An alternative taxonomy of the group has been proposed including the families Acratocnidae and Parocnidae within a new superfamily, Megalocnoidea. Based on White and MacPhee (2001): and Vinola-Lopez et al. 2022 For other sloth taxa of the Caribbean, see Pilosans of the Caribbean . The following sloth family phylogenetic tree
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#17328766479381188-519: The anatomy of their limbs, that Neocnus and Acratocnus were likely climbing animals. The taxonomy of Caribbean sloths is in flux, with the number of species present among the Pleistocene - Holocene taxa in question; some species are likely junior synonyms , while the diversity of some genera is probably understated. The mitochondrial DNA study suggests that Acratocnus ye and Parocnus serus are deeply divergent from each other, having split during
1242-429: The base of the tree; 2) cover feces and avoid predation; 3) chemical communication between individuals; 4) pick up trace nutrients in their claws, that are then ingested; and 5) favor a mutualistic relationship with populations of fur moths. More recently, a new hypothesis has emerged, which presents evidence against the previous ones and proposes that all current sloths are descendants from species that defecated on
1296-481: 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 . 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
1350-519: The elements while they hang upside down. In most conditions, the fur hosts symbiotic algae, which provide camouflage from predatory jaguars , ocelots , and harpy eagles . Because of the algae, sloth fur is a small ecosystem of its own, hosting many species of commensal and parasitic arthropods . There are a large number of arthropods associated with sloths . These include biting and blood-sucking flies such as mosquitoes and sandflies , triatomine bugs , lice , ticks and mites . Sloths have
1404-511: 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). 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
1458-437: The environment, normally ranging from 25 to 35 °C (77 to 95 °F), but able to drop to as low as 20 °C (68 °F), inducing torpor . The outer hairs of sloth fur grow in a direction opposite from that of other mammals. In most mammals, hairs grow toward the extremities , but because sloths spend so much time with their limbs above their bodies, their hairs grow away from the extremities to provide protection from
1512-591: 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
1566-528: 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. 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
1620-496: The familial life of Megalonyx . An adult was found in direct association with two juveniles of different ages, suggesting that adults cared for young of different generations. The earliest known North American megalonychid, Pliometanastes protistus , lived in Florida and the southern U.S. about 9 million years ago, and is believed to have been the predecessor of Megalonyx . Several species of Megalonyx have been named; in fact,
1674-432: 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. In Peru and Chile , Thalassocnus entered
Megalonychidae - Misplaced Pages Continue
1728-743: The ground but are able to swim. 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. 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. One study found that xenarthrans broke off from other placental mammals around 100 million years ago. 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
1782-462: The ground, and there simply has not been enough selective pressure to abandon this behavior, since cases of predation during defecation are actually very rare. Baby sloths learn what to eat by licking the lips of their mother. All sloths eat the leaves of Cecropia . Two-toed sloths are omnivorous , with a diverse diet of insects , carrion , fruits , leaves and small lizards , ranging over up to 140 hectares (350 acres). Three-toed sloths, on
1836-472: The ground. Sloths are surprisingly strong swimmers and can reach speeds of 13.5 m (44 ft) per minute. They use their long arms to paddle through the water and can cross rivers and swim between islands. Sloths can reduce their already slow metabolism even further and slow their heart rate to less than a third of normal, allowing them to hold their breath underwater for up to 40 minutes. Wild brown-throated three-toed sloths sleep on average 9.6 hours
1890-438: The large energy expenditure and dangers involved in the journey to the ground, this behaviour has been described as a mystery. Recent research shows that moths, which live in the sloth's fur, lay eggs in the sloth's feces. When they hatch, the larvae feed on the feces, and when mature fly up onto the sloth above. These moths may have a symbiotic relationship with sloths, as they live in the fur and promote growth of algae, which
1944-402: The largest mammals native to the Caribbean islands with the largest species Megalocnus rodens estimated to weigh around 146 kilograms (322 lb) or 270 kilograms (600 lb), with the smallest genera Neocnus and Acratocnus estimated to only weigh 8–15 kilograms (18–33 lb). Like other sloths megalocnids were probably folivores, with some authors suggesting that based on
1998-509: The latter are more closely related to mylodontid sloths. The megalonychids plus nothrotheriid and megatheriid sloths, together with living three-toed sloths , make up the sloth superfamily Megatherioidea . Megalonychidae, along with all other mainland ground sloths became extinct in North and South America around the end of the Late Pleistocene , approximately 12,000 years ago, as part of
2052-634: The mainland, but then went extinct when humans finally colonized the Greater Antilles. Sloths can be 60 to 80 cm (24 to 31 in) long and, depending on the species, weigh from 3.6 to 7.7 kg (7.9 to 17.0 lb). Two-toed sloths are slightly larger than three-toed sloths. Sloths have long limbs and rounded heads with tiny ears. Three-toed sloths also have stubby tails about 5 to 6 cm (2.0 to 2.4 in) long. Sloths are unusual among mammals in not having seven cervical vertebrae . Two-toed sloths have five to seven, while three-toed sloths have eight or nine. The other mammals not having seven are
2106-405: The mainland. On Cuba the latest date for Megalocnus is calibrated 4700 years Before Present (BP). approximately 2700 BC. while dates for Parocnus browni are around 6250 BP (4250 BC). On Hispaniola the dates for some indeterminate sloth specimens are around 5000 BP (3000 BC); these dates roughly coincide with the first settlement of the Caribbean, which suggests that humans were the cause of
2160-603: The morphological evidence collected to support the hypothesis of diphyly has been based on the structure of the inner ear. Recently obtained molecular data from collagen and mitochondrial DNA sequences 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
2214-422: The other hand, are almost entirely herbivorous (plant eaters), with a limited diet of leaves from only a few trees, and no other mammal digests its food as slowly. They have made adaptations to arboreal browsing. Leaves, their main food source, provide very little energy or nutrients, and do not digest easily, so sloths have large, slow-acting, multi-chambered stomachs in which symbiotic bacteria break down
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2268-659: 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. The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data. Megalocnidae (Greater Antilles sloths) Scelidotheriidae Mylodontidae Choloepodidae (two-toed sloths) Megalonychidae Bradypodidae (three-toed sloths) Nothrotheriidae Megatheriidae The marine sloths of South America's Pacific coast became extinct at
2322-419: The size of the huge Late Pleistocene Megalonyx jeffersonii from the last ice age . It was formerly believed, based on morphological comparisons, that Greater Antilles sloths and extant arboreal two-toed sloths were part of this family. However, molecular results based on sequences from collagen and mitochondrial DNA have shown that the former represent a basal branch of the sloth radiation, while
2376-587: The sloths eat. Individual sloths tend to spend the bulk of their time feeding on a single "modal" tree; by burying their excreta near the trunk of that tree, they may also help nourish it. The pale- and brown-throated three-toed sloths mate seasonally, while the maned three-toed sloth breeds at any time of the year. The reproduction of pygmy three-toed sloths is currently unknown. Litters are of one newborn only, after six months' gestation for three-toed, and 12 months for two-toed. Newborns stay with their mother for about five months. In some cases, young sloths die from
2430-455: The taxonomic suborder Folivora 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 ( † ): The common ancestor of
2484-399: The tough leaves. As much as two-thirds of a well-fed sloth's body weight consists of the contents of its stomach, and the digestive process can take a month or more to complete. Three-toed sloths go to the ground to urinate and defecate about once a week, digging a hole and covering it afterwards. They go to the same spot each time and are vulnerable to predation while doing so. Considering
2538-492: The two existing sloth genera dates to about 28 million years ago, 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". 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
2592-600: The wild is currently unknown due to a lack of full-lifespan studies in a natural environment. Median life expectancy in human care is about 16 years, with one individual at the Smithsonian Institution's National Zoo reaching an age of 49 years before her death. Although habitat is limited to the tropical rainforests of Central and South America, in that environment sloths are successful. On Barro Colorado Island in Panama , sloths have been estimated to constitute 70% of
2646-458: The wild. However, a report in May 2016 featured two former veterinarians from the facility who were critical of the sanctuary's efforts, accusing it of mistreating the animals. Megalocnidae Megalocnoidea Delsuc et al, 2019 Megalocnidae is an extinct family (alternatively considered to be a superfamily as Megalocnoidea ) of sloths , native to the islands of the Greater Antilles from
2700-923: The work of Stinnesbeck and colleagues (2021). (Note that this tree does not conform to genetic studies, as it includes the Caribbean sloths Neocnus , Parocnus Megalocnus and Arcatocnus which have been placed in the separate family Megalocnidae , well as the two toed sloths ( Choloepus ), which are placed in the clade Mylodontoidea ). Megalonychotherium Eucholoeops Megalonyx Pliometanastes Pliomorphus Megalocnus Parocnus Neocnus Acratocnus Choloepus Ahytherium Megistonyx Xibalbaonyx Nohochichak Meizonyx Zacatzontli Total evidence phylogeny after Tejada et al. 2023. Megalonychotherium Pliometanastes Megalonyx Australonyx Ahytherium Megistonyx Sloths Sloths are
2754-485: 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. 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
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#17328766479382808-726: Was hoping they would find some living in the Western range. Megalonyx jeffersonii was named after Thomas Jefferson in 1822. The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig. 4 of Presslee et al ., 2019). † Megalocnidae (Caribbean sloths) † Scelidotheriidae † Mylodontidae Choloepodidae (two-toed sloths) † Megalonyx jeffersoni Bradypus torquatus Bradypus pygmaeus Bradypus tridactylus Bradypus variegatus † Nothrotheriops shastensis † Megatherium americanum A morphological tree of Megalonychidae, based on
2862-532: Was likely arboreal and similar in weight to extant tree sloths, at less than 10 kilograms. It is thought that sloths arrived in the Caribbean from South America (where they arose) around the Eocene-Oligocene boundary about 33 million years ago, when there was a significant sea level drop caused by a glaciation episode. This has been associated with the GAARlandia (Greater Aves Antilles Ridge) hypothesis, where
2916-566: Was the case for Megatherium . 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
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