Chubutherium

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Xenarthra
Family: Mylodontidae
Genus: Chubutherium
Species: S. leptocephalum
               S. parodii
Conservation Status: Extinct
Temporal Range: Oligocene - Mid Miocene

Chubutherium ferelloii is an extinct species of ground sloth. They first appeared in the Oligocene and died out during the Middle Miocene. It is related to the Pleistocene genus, Scelidotherium. Only a few specimens have been found in Patagonia.

Scelidotherium

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Xenarthra

Family: Mylodontidae

Genus: Scelidotherium

Species: S. leptocephalum

               S. parodii 

Scelidotherium is an extinct genus of ground sloth of the family Mylodontidae, endemic to South America during the middle Pleistocene epoch. It lived from 780,000 - 11,000 years ago. They existed for approximately 0.67 million years.

It is characterized by an elongated, superficially anteater-like head. It is known almost exclusively from Argentina, but its distribution may have extended into Paraguay and Uruguay.

The meaning of their name is femur Beast.

They were 3.6 ft tall and about 3000 kgs.

Paramylodon

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Pilosa

Family: Mylodontidae

Genus: Paramylodon

Species: P. harlani

Temporal Range: Late Pliocene to Pleistocene (4.9 ma - 11,000 years ago)

It is an extinct genus of ground sloth of the family Mylodontidae endemic to North America during the Pliocene through Pleistocene epochs.

Paramylodon was about 9.8 ft in height and weighted as much as 1000 kg. It is known from North America deposits, including in Mexico and the United States and as far south as Guatemala. Currently there is just one recognized species, P. harlani. 

Recently a Paramylodon specimen was identified from the Tarkio Vallet site in Lowa association with Megalonyx. This is probably the first time these species have been found in close association. These two species have since been uncovered at  the Fairmead Landfill Site and Irvington Site in California.

Mylodon

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Pilosa

Family: Mylodontidae

Genus: Mylodon

Species: M. darwini

Temporal Range: Pleistocene to Holocene

It is a extinct genus of ground sloth that lived in the region South America until roughly 10,000 years ago. Exactly the fossil remains found in Argentina and Chile.

Mylodon's close relatives include the ground sloths of the genera has often been confused with Glossotherium and Paramylodon. Scientists often confused Mylodon with Glossotherium. 

Mylodon weighed about 2,500 kg and stood up to 10 ft when raised up on its hind legs. It had very thick hide and had osteoderms within its skin for added armor. Because of this armor and its long and sharp claws, it is unlikely that the Mylodon had any natural enemies other than humans, who would have still difficult to pierce with stone projectile points.

Mylodon has been traditionally considered a grazer in open areas, which is theorized based on its paleoenvironment as well as from the vegetation found in fossilized dung. However new study suggests that they  had been a mixed or selective-feeder instead and the paleoenvironment of the formation where the animal was found indicates a wide variety of vegetation to be selected from. 

The Mylodon had a wide range of climate and environment tolerance. It was probably capable of inhabiting arid to semiarid and cold climates, humid and warm climates and cooler and montane climates.

Lestodon

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Pilosa

Family: Mylodontidae

Genus: Lestodon

Species: L. armatus

Temporal Range: Pleistocene

It is an extinct genus of megafaunal ground sloth from South America during the Pleistocene period. Its fossil

remains have been found in Argentina, Paraguay, Uruguay and Bolivia. 4.6 (15ft) from snout to tail tip, it is estimated to have weighted about 4 tons. It was a herbivore and primarily fed on the grasses on the South American Plains and is thought to perhaps have used its semi-bipedal stance to obtain foliage from trees. The genus name Lestodon derives from the Greek for robber tooth.
Lestodon had a large, blunt and square mandible well adapted for foliage consumption. Its muzzle and dentition show significant adaption to this diet. The shape of the muzzle aided the ground sloth in the grazing necessary to sustain the metabolic activity of its large body, square,flat muzzles are associated with bulk feeders while pointed snouts are adaptive features of precision eaters. To sustain its coloric needs with plant matter, the sloth would have needed to be able to consume a high quantity of food with little precision. The species would dig its food, and would have accidentally ingested a large amount of grinity dirt and soil particulate. This gives them a large crown height, called hypsodonty that is unsuitable for strong bite forces. While the mandibular muscles would have been well developed to support the allometrically positive jaw of Lestodon, they would have also been extremely weak.
Researchers working at the Arroyo del Vizcaino site near Sauce, Uruguay, found evidence suggesting that Lestodon was hunted by humans about 30,000 years ago. This was discovered through the analysis of Lestodon bones. Deep slash markings on some of them were discovered the use of human stone tools.

Glossotherium

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Xenarthra

Family: Mylodontidae

Genus: Glossotherium

Species: G. robustum

               G. chapadmalense

Temporal Range: Late Pliocene to Early Holocene (2.5 - 0.010 ma)

Its literal meaning is the Tongue Beast. It was a genus of ground sloth which was heavily built animal with a length of about 13 ft snout to tail-tip and a weight estimated at 1000 kg. They could potentially assume a slight bipedal stance.

They are generally wider and more robust with a dignostic increased amount of lateral flare at the predental spout. 

G. robustum was endemic to South America and weighted about 1500 kg. Pleistocene records indicate that it was widely distributed between 20 degree south to 40 degree south with a range spanning across Argentina, Chile, Uruguay, and Paraguay.

Sloths have ever-growing adult dentition. They lack deciduous dentition and have a reduction in tooth number. Sloth teeth also lack the enamel and cuspation pattern generally present in other mammals. Their tooth forms are oval, sub-rectangular or elongate irregular ovoid. cheek teeth in Glossotherium are larger, have more complex shapes and retain more of the cementum layer around all sides of each tooth than the shasta ground sloth and tree sloths.

Their diet is still unclear. However based on the dental evidence, it was likely more suited to grazing, though it was also probably less efficient at ingesting grasses since its dental apparatus was more suited to shearing which would have been too ineffective at processing plant materials down to an ingestible size to obtain adequate nutritive value. They have a very slow rate of passage of food through the gut. They could probably survive better on foods of lower nutritional value than other sloths could. They likely ate grasses, but also probably they ate a variety of foliage as well and would be better considered a browser-grazer than simple grazer.

They use the same way what the elephants do to communicate. sloths may have used low frequency sounds in melting calls or other social interactions of for long-range sound sensing as in predator-prey interactions or weather forecasting. Another possible explanation for hearing in low frequencies may be due to forssorial habits: low hearing frequencies coupled with a short interaural distance suggest that Glossotherium probably had very poor sound localization.This indicates evidence of an underground lifestyle since loss of high frequency hearing is common to fossorial mammals. Their huge nostrils were likely effective for sound emission with expanded nares possibly related to emission of low frequency sounds up to 600 Hz.

Due to its size and strength, Glossotherium would have had few natural enimies apart from Smilodon. It is believed to have died out in the Pleistocene (1.8 - 12,000 years ago). The most recent reported date is about 8700 years ago.

They have been found in South America and Mexico. It is closely related to Paramylodon of North America.Earliest Glossotherium specimens are known from the Pliocene of South America and are represented by the species, G. chapadmalense. All speciemens of Pleistocene age are typically lumped into G. robustum and a few other quentionalbe species. Further research is needed at the species level.

Mylodontidae

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia

Order: Pilosa
Family:  Mylodontidae
Mylodontidae is a family of extinct ground sloths which  lived about 22.89 million years from 23 million years ago to 11,000 million years ago.

Genus

• Glossotherium
• Lestodon
• Mylodon
• Paramylodon
• Scelidotherium
• Chubutherium

Pronothrotherium

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Xenarthra
Family: Nothrotheriidae
Genus: Pronothrotherium
Species: P. typicum
Temporal Range: Miocene

It is an extinct genus of ground sloth of South America. They were from the Miocene Epoch. They may be familiar with the Marine life.

Nothrotherium

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Xenarthra

Family: Nothrotheriidae

Genus: Nothrotherium

Species: N. maquinense Lund

               N. escrivanense

 It is an extinct genus of medium-sized ground sloth from South America and Mexico. It differs from Nothrotheriops in smaller size and differences in skull and hind leg bones, but genera can be traced back to Hapolops, the genus which both evolved from in different ecoloogical conditions. These browsing ground sloths consumed roots, stems, seeds and leaves of various desert plants, such as the yucca and agave.

Hapalops

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Xenarthra

Family: Megatheriidae
Species: H. indifferens
               H. longiceps
               H. latus
               H. cadens
               H. congermanus
               H. gallaicus

Conservation Status: Extinct

Temporal Range: Late Oligocene - Miocene

Hapalops is extinct genus of ground sloth from the late Oligocene of South America. Though related to the giant Megatherium, Hapalops was much smaller, measuring about 1 meter in length. Like most extinct sloths it is categorized as a ground sloth, but it is believed that the smaller size of Hapalops allowed it to engage in some climbing behaviors.

It had a robust body, short skull and long limbs with large, curved claws. When it did visit the ground the animal probably walked on the knuckles of its forelimbs, like gorilla. Hapalops had very few teeth with no incisors, the mandible included only four pairs of teeth.

Hoffmann's Two-Toed Sloth

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Pilosa

Family: Megalonychidae

Genus: Choloepus
Species: C. hoffmanni

Conservation Status: LC (Least Concerned)

Hoffmann's tow-toed nocturnal and arboreal animal, found in mature and secondary rainforests and deciduous forests. The common name commemorates the German naturalist Karl Hoffmann.

Description

This sloth is a heavily built animal with shaggy fur and slow, deliberate movements. The fore feet have only two toes, each ending with long, curved claws, The three toes sloth also have these same characteristics which may be found in the same geographic areas, but there are some characteristics that definitely distinguished them from the two toed sloths. Those characteristics include they have the longer snout, separate rather than partially fused toes of the forefeet, the absence of hair on the soles of the feet, and larger overall size. The wrist of the sloth has developed some specific traits due to their slow, yet acrobatic motions. These evolved traits include diminution and distal migration of the pisiform bone. with a loss of contact with the ulna; reduction of the distal end of the ulna to a styloid process, and extremely reduced contact between the ulna and triquetral bone.

This Hoffmann's two-toed sloth is very much related with Linnaeus's two-toed sloth. These two are also very closely resembles. The primary physical differences between the two species relate to suitable skeletal features.
Adults range from 54 to 72 cm in head-body length and weigh from 2.1 to 9 kg. Although they do not have stubby tails, just 1.5 to 3 cm long, this is too short to be visible through the long fur. The claws are 5 to 6.5 cm long. Females are larger on average than males, although with considerable overlap in size. Their fur is tan to light brown in colour, being lighter on the face, but usually has a greenish tinge because of the presence of algae living in the hairs.

Habitat

this sloth inhabits tropical forests from sea level to to 3300 m above sea level. It is found in the rainforest canopy in two separate regions of Central and South America, separated by the Andes. One population is found from eastern Honduras in the north to western Ecuador in the south and the other in eastern Peru, Western Brazil and northern Bolivia. According to the study a divergence date of about 7 million years between these populations has been suggested.

 

Behavior

Two-toed sloth spend most of their time in trees, through they may travel on the ground to move to a new tree. A new study suggests on Barro Colorado Island, these species of sloth is exclusively nocturnal, even though in other locations they are known to be active during day. This is may be because of the competition with brown-throated sloth. They often move slowly through the canopy for about eight hours each night, and spend much of the day sleeping in tangles of lianas, They move only very slowly, typically at around 0.14 m/s, although they can move up to 50% faster when excited. They are solitary in the wild and aside from mothers with young, it is unusual for two be found in a tree at the same time.
Sloths have very poor eyesight and hearing and rely almost entirely on their sense of touch and smell to find food. This sloth is often spits when the mouth opens.

Diet

Their main source of diet is tree leaves. Though they also eat fruits and flowers. Sloths have three chambered stomachs. A sloth may take up to a month to completely digest a meal and up to two-thirds of a sloth's weight may be the leaves in its digestive system.

Predators

Sloths have many predators, including the jaguars, ocelots, harpy eagles, margays and anacondas.. If threatened, sloth s can defend themselves by slashing out at a predator with their huge claws or biting with their sharp cheek teeth. However, a sloth's main defense is to avoid being in the first place. The two-toed sloth can survive wounds that would be fatal to another mammal its size. The sloth's slow, deliberate movements and algae-covered fur make them difficult for predators to spot from a distance. Their treetop homes are also out of reach for many larger predators.

 

Life Cycle

Courtship consists of the female licking the male's face and rubbing her genitals against the male's body. Gestation lasts between 355 and 377 days, and results in the birth of a single young. The birth takes place in either the ground or in the hanging position. Newborn sloths weight 340 to 454 g. from birth they have long caws and able to cling to their mothers' undersides. The begin to take solid food at 15 to 27 days and are fully weaned by 9 weeks. young sloths make loud bleating alarm calls if separated from their mothers.
Hoffmann's sloth reach sexual maturity at two to four years of age and have been reported to live up to 32 years in captivity.

Conservation Status

Habitat destruction is probably causing a decrease in the wild Hoffmann's two-toed sloth population but little reliable data is available on the number of wild individuals. Sloths and people have little contact with one another in the wild.

Choloepus

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Pilosa

Family: Megalonychidae

Genus: Choloepus
Species: C. didactylus
               C. hoffmanni
Temporal Range: Late Miocene to Recent

Choloepus is a genus of living sloth which lived in Central and South America, within the family Megalonychidae consisting of two-toed sloths. This is the only surviving genus of the family Megalonychidae which has two species, Linnaeus's two-toed sloth and Hoffmann's two-toed sloth.

Relation to the three-toed sloth

The relationship between the two-toed and three-toed sloth is not close. According to study it is confirmed that the two genera are not closely related and each adopted its arboreal lifestyle independently. It is unclear from which (if any) ground dwelling sloth the three-toed sloths evolved; the two-toed sloths appear to nest phylogenetically within one of the divisions of Caribbean megalonychids, and thus probably either descended from them or are part of a clade that invaded the Caribbean multiple times. Though data has been collected on over 33 different species of sloths just by analyzing bone structures, many of the relationships between clades on a phylogenetic tree are unknown. Both types tend to occupy the same forests; in  most areas, a particular species of three-toed sloth and a single species of the larger two-toed type will jointly predominate.

Each genus of sloth has a common ancestor, but what that ancestor was, when it existed, and many of its traits remain virtually unknown. There is relatively little evidence to support the hypothesis of diphyly and only a small amount of data to study overall.In fact, most of the evidence of support the hypothesis of diphyly  is still heavily based on the same trait that cause the hypothesis to be suggested; the structure of the inner ear.

One of the largest problems that exists when attempting to identify clades of modern tree sloths is the issue of missing links between surviving, living species and their unidentified common ancestors. There are several families of extinct sloths, about which very little is known. The missing information causes large holes in phylogenetic trees and makes tracing paths of evolution a daunting task. As a result, there are many versions of the phylogenetic tree that would describe the evolution and relationship between sloths, most of which conclude that convergent evolution is the likely mechanism that resulted in today's genera of tree sloths. Despite a couple of discrepancies in DNA sequencing, it is largely accepted that extant tree sloth species of genera Choloepus and Bradypus do not share a recent common ancestor, making them diphyletic to one another and indicating similarities through convergent evolution.. This means that the two extant genera evolved analogous traits, such as locomotion methods, size, habitat and many other traits independently. from one another as opposed to from their last common ancestor.

If the theory of convergent evolution between the two species were accepted  as true, that would make sloths one of the most striking examples of convergent evolution known among mammals. In order to further support this theory, there would need to be more information and data gathered about intermediate species between the extant species and the common ancestor, which is estimated to have gone extinct over 30 million years ago.

A study of retrovirus and m-DNA suggests that C. didactylus and C. hoffmanni diverged six to seven million years ago. Furthermore, based on cytochrome c oxidase subunit I sequence, a similar  divergence date (~7mya) between the two populations of C. hoffmanni separated by the Andes has been reported.

Characteristics

The name two-toed sloth erroneously describe the number of toes. They have two fingers in their hands (in the thoracic limbs) and three toes in their feet (in the pelvic limbs). The name two-toed sloth is misleading, although widely used. The name was intended to describe specific anatomical differences between members of the genus Choloepus and Bradypus. However to accurately describe these differences, the correct name should be two fingered sloth (Choloepus spp) as the differences occur in the hands and not in the feet. They are also larger than tree-toed sloths, having a body length of 58 to 70 cm and weighing 4 to 8 kg. other distinguishing features include a more prominent snout, longer fur, and the absence of a tail.

two-toed sloths have a reduced, ever growing dentition with neither incisors nor true canines, which overall lacks homology with the dental formula of other mammals. Their first tooth is very canine-like in shape and is referred to as a caninoform. It is separated from the other teeth or molariforms by a diastema. The molariforms are used specifically for grinding and are mortar and pestle-like in appearance and function. Thus, they can grind food for easier digestibility, which takes the majority of their energy.They dental formula of two-toed sloths is: 4/5 (unau)

Two-toed sloths are unusual among mammals in possessing as few as five cervical verrtebrae, which may be due to mutations in the homeotic genes. All otehr mammals have seven cervical vertebrae. Other than the  three-toed sloth and the manatee.

Feeding

They eat primarily leaves, but also shoots, fruits, nuts, berries, bark, some native flowers and even some small rodents. When they can not find food they have been known to eat the algae that grow on their fur for nutrients. They have large stomachs with multiple chambers, which help to ferment the large amount of plant matter they eat. Food can take up to a month to digest due to their slow metabolism. Depending on when in the excretion cycle a sloth is weighed, urine and feces may account for up to 30% of the animal's body weight which averages about 6 kg. They get their water from juicy plants.

Behaviour

The two-toed sloths most of their lives hanging upside down from trees. They cannot walk, so they pull hand-over-hand to move around which is at an extreme slow rate. Being predominantly nocturnal, their fur which grows greenish algae to blend in, is their main source of protection. Their body temperatures depend at least partially on the ambient temperature; they cannot shiver to keep warm, as other mammals do, because of their unusually low metabolic rates and reduced musculature. The-toed sloths also differ from three-toed sloths in their climbing behavior, preferring to descend head first.

Life Cycle

Two-toed sloths have a gestation period of six months to a year, depending on the exact species. The mother gives births to a single young while hanging upside down. The young are born with claws and are weaned after about a month, although they will remain with the mother for several more months and do not reach sexual maturity until the age of three years, in the case of females or four to five years, in the case of males.

Neocnus

Kingdom: Animalia
Phylum: Chordata
Class: Mamallia
Order: Pilosa
Family: Megalonychidae
Genus: Neocnus
Species: N. gliriformis
               N. major
               N. comes
               N. dousman
               N. toupiti
Conservation Status: Extinct
Temporal Range: Pleistocene

 Neocnus is an extinct genus of ground sloth, whose species ranged across Cuba and Hispaniola. Neocnus would have resembled a typical megalonychid ground sloth, though much smaller, with a longer tail and broad trunk, as well as lissome limbs and long claws. This sloth was known for having caudal vertebrae that were broad, a trait shared with other ground sloths, indicating that this animal like the tamandua of today, likely used its tail to stand  upright. The caniniform teeth of the Neocnus were large and triangular, and its skull was deep and large. 

The fossils of this sloth were found in Haitian cave deposits. They have been dated to as recently as 4391 BP, calibrated to 5000 BP. It is theorized that this sloth, in common with other Antillean sloths was killed off by humans seeking its pelt and meat. Currently, this species of sloth is being studied by evolutionary historians. Neocnus is suspected of having been semi-arboreal.

Megalocnus

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Pilosa
Family: Megalonychidae
Genus: Megalocnus
Species: M. redens
               M. zile
Conservation Status: Extinct
Temporal Range: Late Pleistocene to Holocene

The ground sloths of the extinct genus Megalocnus were among the largest of the Caribbean ground sloths, with individuals estimated to have weighted up to 90 kg when alive. Two species are known, M. rodens of Cuba and M. zile of Hispaniola. Megalocnus means great sloth. According to the fossil reports M. redens indicate survival well into the Holocene.

Imagocnus

 

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Xenarthra

Family: Megalonychidae

Genus: Imagocnus

Species: I. zazae

 Temporal Range: Early Miocene 

Imagocnus is an extinct genus of ground sloth from the early Miocene of Cuba.This sloth resided in the Antilles and showed a range of body size. Its relationships to other Antilean sloths are not immediately clear, though the genera Megalocnus and Parcnus other ground sloths are its most likely relatives. Not much details is known about this genus of sloth due to lack of fossil evidence. Though it is believed that this genus of sloth did not lived for a long time period for some unknown reason.

Habanocnus

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Xenarthra
Family: Megalonychidae
Genus: Habanocnus
Species: H. hoffstetteri
               H. paulacounto

Habanocnus is an extinct genus of ground sloth. It is also known as the Havana Sloth. It is  indigenous to Late Pleistocene Cuba. There is not much significant excavation of these spices with what we can get some identification. What we gather, we can only say that Acratocnus and Habanocnus are taxonomic synonyms. There is not much identificational difference between these to genus.

Acratocnus

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Pilosa

Family: Megalonychidae

Genus: Acratocnus
Species: A. odontrigonus
              A. antillensis
              A. ye

Temporal Range: 2.5 mya - 5000 BP (Pleistocene to Holocene)

Acratocnus is an extinct genus of ground sloth found in Cuba, Hispaniola and Puerto Rico. It is a member of the family Megalonychidae, whose sole surviving genus is Choloepus (the two toed tree sloth)

 

HABITAT

The species of Acratocnus were found on the islands of Puerto Rico, Cuba and Hispaniola, where they inhabitat the montane forests of the highlands. The Puerto Rican ground sloth, Acratocnus odontrigonus is known from several poorly documented cave excavations in northwestern Puerto Rico. The various species are regarded as being semi-arboreal because of their small size and their large hooked claws.

SIZE

The various species of Acratocnus ranged in different weights. their weight varied from 22kg to 70 kg.This indicates that they are much larger than the living tree sloths as those are not more than 15 kg.

 

EXTINCTION

As with many sloth fossils, these species of sloth have not been radio-metrically dated. It is suggested that the Puerto Rican and Hispaniolan Acratocnus species survived into the late Pleistocene but disappeared by the mid-Holocene. According to the latest survival reports it is confirmed that there is no evidence of any kind of ground sloth in Cuba after 5000 BP. The causes of their extinction may have been climate changes or more likely human hunting or any kind of plague.

Megalonyx

Kingdom: Animalia
Phylum: Chordata
Order: Pilosa
Family: Megalonychidae
Genus: Megalonyx
Species: M. matthisi
               M. wheatieyi
               M. leptostomus
               M. jeffersonii

Conservation Status: Extinct
Temporal Range: Miocene to Pleistocene 

Megalonyx is an extinct genus of giant ground sloths of the family Megalonychidae endemic to North America from the Hemphillian of the Late Miocene through to the Rancholabrean of the Pleistocene, living from around 10. 3 Million years ago to 11,000 years ago, existing for approximately 10.289 million years.

DESCRIPTION

Megalonyx certainly does not look like a sloth, it was a large, heavily built animal about 9.8 feet (3m) long. Its maximum weight is estimated at 1000 kg. This is medium-sized among the giant ground sloths. It is of the size of an American Bison. Like other ground sloths it had a blunt snout, massive jaw, and large peg-like teeth.

 HIND LEGS

It was not like the usual sloths what we have seen in the jungles of South America, it was built for living on the ground. Their hind was built like human feet, i.e. Megalonyx walked with heel, foot and toe bones all on the ground just what we do. This provided good surface area for carrying weight and better balance when the stood up. This is called 'Plantigrade' by the biologists. This provided good surface area for carrying weight and better balance when Megalonyx stood up. And Megalonyx probably spend a lot of time standing in order to eat. To give this giant ground sloth added stability and to ease the stress on its massive hind legs.

 TAIL

Except their massive legs the have a thick, muscular tail which is very rare for the land mammals. Its massive hips gave ample area for strong muscles, while Megalonyx spent time ripping down and feasting on soft leaves and fruit from the trees.

ARM

Bending down those huge branches to reach its mouth was the job of the Megalonyx's powerful arms. The arm and shoulder bones are large and have wide wings and large knobs where big muscles attached. Each of the three fingers on the hand was equipped with large, powerful claws upto 8 inches or 20 cm long. Unlike the claws of the modern lion these giant claws were mostly used to grasp and tear up branches and leaves. However, they also made for a very effective defense against the predators. One swipe of the arm of the Megalonyx may have been more powerful than a grizzly bear.

TEETH

One of the most peculiar anatomical  feature of sloths is their teeth, which lack the hard enamel found in the humans and nearly all other mammals. Instead, sloths possess simple peg-like molar (back) teeth made primarily of the material dentin. Dentin is much softer than enamel and wears out faster. The sloths teeth never stop growing. Because of this, Megalonyx could keep on eating even if a tooth was damaged, since the damaged part would wear out and be replaced by healthy dentin over time. Inlike nearly all other mammals, Megalonyx never had to worry about a chipped tooth.

TAXONOMY

The generic name Megalonyx was proposed by future U.S. President Thomas Jefferson in 1797, based on fossil specimens of what later came to be called Megalonyx jeffersonii that he had received from western Virginia. His presentation to the American Philosophical Society that year is often credited as the beginning of vertebrate paleontology  in North America. However, Jefferson's name has no validity in zoological nomenclature, and Megalonyx was first formally named by Richard Harian in 1825.

 

EVOLUTION

Megalonyx evolved from ancestors that island-hopped across the Central American Seaway from South America, where ground sloths arose, prior to formation of the Panamanian land bridge. Its appearance in North America thus predates the bulk of the faunal exchange between North and South America. Its immediate predecessor was Pliometanastes and its closest living relatives are the two toed sloths (Choloepus).
M. jeffersoni lived from the Illinoian Stage during the Middle Pleistocene (150,000 years BP) through to the Rancholabrean of the Late Pleistocene (11,000 BP). It belongs to the genus Megalonyx, a name proposed by Thomas Jefferson, future president of the United States, in 1797. M. jeffersoni was probably descended from M. wheatieyi, which was in turn was probably derived from M. leptostomus. This was named by Cope (1893). This species lived from Florida to Texas, north to Kansas and Nebraska, and west to New Mexico, Nevada, Oregon, and Washington. It is about half the size of M. jeffersoni.

 

HABITAT

Megalonyx ranged over much of North and Central America. Their remains have been found as far north as Alaska and the Yukon.

M.jeffersonii was apparently the most wide ranging giant ground sloth. Fossils are known from many Pleistocene sites in the United States, including most of the states east of the Rocky Mountains as well as along the west coast. It was the only ground sloth to range as far north as the present-day Yukon and Alaska.

The first specimen  ever found in the Colorado was discovered at the Ziegler Reservoir site near Snowmass Village. The Firelands ground sloth fossils dated between 11,727and 11,424 B.C. represents the earliest known hunting activity by Ohioan Paleoindians.

SOCIAL BEHAVIOR

Aside from the basics of the size, food choice and general mobility it is often difficult to learn details of the life habits of animals from their fossils. But recently from an ongoing excavations at Tarkio valley in southwest lowa may reveal something of 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.

Megalonychidae

Temporal Range:  35 Mya - 0 Mya

OVERVIEW

                      Megalonychidae is a group of sloth that includes the extinct ground sloth and the living two toed sloth. Megalonychidae first appeared in the early Oligocene, about 35 million years ago, in Southern Argentina (Patagonia), and as far as the Antilles by the early Miocene. Megalonychids first reached North America by island hopping, about 9 million years ago. prior to the formation of the Isthmus of Panama.
                        Megalonychid ground sloths went extinct in North and South America around the end of the Pleistocene and in the Antilles apparently by about 5000 BP, living two-toed sloths of genus Choloepus as the only surviving member of the family.

EVOLUTION

                        Megalonyx means giant claws. Megalonyx is widespread North American genus that lived past in the close of the last Ice Glaciation. Remains of Megalonyx have been found as far north as Alaska to the Yukon. Ongoing excavations at Tarkio Valley in southwest Iowa may reveal something of 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; actually most of the good specimen described as 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.

Pale Throated Sloth

 

Scientific Classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Superorder: Xenarthra
Order: Pilosa
Suborder: Folivora
Family: Bradypodidae
Genus: Bradypus
Species: B. tridactylus
Conservation Status: LC (Least Concerned)

OVERVIEW

                      The pale throated sloth  is a species of three toed sloth that inhabits tropical rainforests in the northern south America. It is similar in appearance to, and often confused with, the brown-throated sloth, which has a much wider distribution. Genetic evidence has been interpreted to suggest the two species diverged only around 400,000 years ago, although the most recent evidence indicates the split was closer to 6 million years.

DESCRIPTION

                     Pale-throated sloths have a rounded head with a blunt nose and small external ears. The limbs are long and weak, with the arms being nearly twice the length of the hindlimbs. The hands and feet each have three digits, armed with long, arched claws, with the middle claw being the largest and most powerful. Males are 45 to 55 centimetres (18 to 22 in) in head-body length, with a short, 4 to 6 centimetres (1.6 to 2.4 in), tail, and weigh from 3.2 to 6 kilograms (7.1 to 13.2 lb). However, the females are noticeably larger, being from 50 to 75 centimetres (20 to 30 in) in length, and weighing 3.8 to 6.5 kilograms (8.4 to 14.3 lb). 

                  The body is covered with coarse guard hairs up to 10 centimetres (3.9 in) long, with a finer undercoat. Green algae live mutualistically  between the microscopic scales on the surface of the guard hairs, giving the sloth a somewhat greenish appearance that serves as camouflage. Adults are blackish-grey over most of the body, with darker patches distributed over the backs, shoulders, and hips. Males have a bright yellow or orange patch on the back, divided by a central black stripe. Pale-throated sloths are difficult to distinguish from the closely related brown throated sloth but as their names have a pale yellow patch on the throat.

                 The eyes are large and forward facing for binocular vision, with round pupils. Unusually, they appear to lack any cone cells in the retina. suggesting that the sloth is unable to see color. Despite its apparently small ears, the pale-throated sloth has excellent hearing; it has also been reported to have a good sense of smell.

                 The sloth has nine cervical vertebrae. A pale-throated sloth can bend its head backwards and forwards through 270° and rotate it through 330°.

HABITAT

 

                   The pale-throated sloth is found only in the tropical forests of northern South America, including Guyana, Suriname, French Guyana, western Venezuela and Columbia and Brazil, north of the Amazon River. 

BEHAVIOR

                  Pale-throated sloths are solitary, herbivorous animals that spend almost their entire lives in trees. Depending on habitat, population densities of anything from 1.7 to 221 per square kilometre.

                  The pale-throated sloth can hang so securely with its hooklike claws that it even falls asleep in this position. It may even stay suspended in the trees for some time after it dies. They have been reported to spend over eighteen hours each day asleep, and move through the tree canopy only very slowly. They periodically descend from the trees to defecate, depositing a pile of small pellets in a hole dug into the ground. Despite their arboreal lifestyle, they are effective swimmers. Their call is a bird-like whistle described as an "ai-ai" sound. 

                 In addition to their mutualism with green algae, pale-throated sloths are also commensal with sloth moths. and with certain species of beetle. These insects live in the sloth's fur, and lay their eggs in its dung, on which their larvae feed. 

DIET

                They eat only leaves, including those of Cecropia, Ceiba, Elizabetha, and Hevea. 

THREATS

                The known predators of these Pale throated sloths are  Jaguars, Anacondas, Harpy Eagle, Margays.

REPRODUCTION

                   Mating takes place in the trees, with the pair either face to face, or with the male on the female's back. The female gives birth to a single infant after a gestation period of about six months. The young are born already fully furred, and with open eyes. The young animal clings to the mother's underside for the first month of life, by which time it has reached a weight of around 300 grams (10 oz). They begin to take solid food at three weeks, and are fully weaned some time after the first month. The young initially have soft greyish-brown fur, which darkens and becomes rougher as they age. They reach sexual maturity at around three years.