Sloth

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Theria
Infraclass: Eutheria
Superorder: Xenarthra
Order: Pilosa
Suborder: Folivora
Family: Bradypodidae
             Megalonychidae
             Megatheriidae
             Mylodontidae
             Nothrotheriidae

OVERVIEW

Sloths are medium sized mammal which are arboreal (tree-dwelling) resident of the jungles of the Central and South America and are known for being slow moving. Extinct sloth species includes a few species of aquatic sloths and ground sloths some of which are attained the size of elephant. Sloths are habitat for other organisms, and a single sloth may be a moth, beetles, cockroaches, ciliates, fungi and algae.

ECOLOGY

Sloths diets consist of buds, tender shoots and leaves mainly of Cecropia tree. Some two-toed sloths have been documented as eating insects, small reptiles and birds as a small supplement of its diet. They have made extraordinary adaptation to an  arboreal. browsing lifestyle. Their main food source is leaves which gives them very little energy or nutrition and do not digest easily. Their tongue has a unique ability to protrude from their mouth 10 to 12 months which is useful to for collecting leaves just out of the reach.



Although they are unable to survive outside the tropical rainforest South and Central America, within that environment sloths are outstandingly successful creature.

EVOLUTION

Sloths are members of the superorder Xenarthra, a group of mammals that appeared in South America about 60 million year ago (Mya). although at least one source puts the date at which sloths and related animals broke off from other placental mammals at about 100 Mya. Also included among the Xenarthra are anteaters and armadilos. The earliest xenarthans were arboreal herbivores with sturdy spines fused pelvises, stubby teeth and small brains.

Ground Sloth fossils

The living sloths belong to one of two families, known as the Megalonychidae (two toed sloth) and Bradypodidae (three toed sloth). The ancestor of these two genera lived about 35-40 Mya, making the living forms stunning examples of convergent or parallel evolution. The two-toed sloths of today are far more closely related to one particular group of ground sloths than to the living three-toed sloths. Whether these ground-dwelling Megalonychidae were descended from tree-climbing ancestors or whether the two-toed sloths are really miniature ground sloths converted (or reverted) to arboreal life cannot presently be determined to satisfaction. The latter possibility seems slightly more likely, because the small ground sloths Acratocnus and Neocnus, which were also able to climb, are among the closest relatives of the two-toed sloths, and these together were related to the huge ground sloths Megalonyx and Megalocnus.
The Evolutionary history of the three toed sloth is not cleared (no close relative or nothing close fossils have been found).

PHYSIOLOGY

Sloth Claws

            In most mammals, hairs grow toward the extremities, but because sloths spend so much time with their legs above their bodies, their hairs grow away from the extremities to provide protection from the elements while the sloth hangs upside down.This fur provides camouflage. Because of the algae, sloth fur is a small ecosystem of its own, hosting many species of non-parasitic insects. Sloths have short, flat heads, big eyes; short snouts, long legs, and tiny ears. Some species have stubby tails (6–7 cm long). Altogether, sloths' bodies usually are between 50 and 60 cm long. Sloths' claws serve as their only natural defense. A cornered sloth may swipe at its attackers in an effort to scare them away or wound them. Despite sloths' apparent defenselessness, predators do not pose special problems: sloths blend in with the trees and move slowly, do not attract attention. Only during their infrequent visits to ground level do they become vulnerable. The main predators of sloths are the Jaguar, the harpy eagle an Humans. The majority of recorded sloth deaths in Costa Rica are due to contact with electrical lines and poachers. Their claws also provide a further unexpected deterrent to human hunters; when hanging upside-down in a tree, they are held in place by the claws themselves and often do not fall down even if shot from below.
Their sense of smell is far better than their eyesight and  hearing.
Despite their adaptation to living in trees, sloths (like many other rainforest animals) make competent swimmers. This is likely to have been true of the extinct ground sloths, as well, as evidenced by the fact that megalonychid sloths were able Colonise the 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 existence of the Isthmus of Panama. Additionally the nothrotheriid Thalassocnus of the west coast of South America became adapted to a semiaquatic marine lifestyle.
Sloths move only when necessary and even then very slowly; they have about a quarter as much muscle tissue as other animals of similar weight. They can move at a marginally higher speed if they are in immediate danger from a predator (4 m or 13 ft per minute for the three-toed sloth), but they burn large amounts of energy doing so. Their specialized hands and feet have long, curved claws to allow them to hang upside down from branches without effort. While they sometimes sit on top of branches, they usually eat, sleep, and even give birth hanging from limbs. They sometimes remain hanging from branches after death. On the ground, the maximum speed of the three-toed sloth is 2 m or 6.5 ft per minute.

Three Toed Sloth Swimming

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. The reason for this risky behavior is unknown, although some believe it is to avoid making noise while defecating from up high that would attract predators.Consistent with this, they reportedly relieve themselves from their branches during storms in the rainy season.

Sloth With Its Cub

Infant sloths normally cling to their mothers' fur, but occasionally fall off but they are very sturdily built and rarely die from a fall. In some cases, they die from 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.
Two-toed sloths have only six cervical vertebrae and three-toed sloths with 9 cervical vertebrae.
Sloths sleeps about 15 to 18 hours each day. Three-toed sloths are mostly diurnal and two-toed sloths are nocturnal.

CLASSIFICATION 

Family: Bradypodidae (Three-toed sloth)

• Bradypus
  • Pale-throated Sloth (Bradypus tridactylus)
  • Brown-throated Sloth (Bradypus variegatus)
  • Maned Sloth (Bradypus torquatus)
  • Pygmy Three-toed Sloth(Bradypus pygmaeus)
   

Family: Megalonychidae (Two-toed and extinct ground sloth)

• Choloepus
  
  • Hoffman's Two-toed Sloth (Choloepus hoffmanni)
  • Linnaeus's Two-toed Sloth (Choloepus didactylus)
   
• Acratocnus
• Habanocnus
• Imagocnus
• Megalocnus
• Megalonyx
• Neocnus

Family: Megatheriidae (extinct ground sloth)

• Eremotherium
• Hapalops
• Megatherium
• Prepotherium
• Promegatherium
• Pelecyodon

Family: Mylodontidae (extinct ground sloth)

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

Family: Nothrotheriidae (extinct ground sloth)

• Mionothropus
• Nothropus
• Nothrotheriops
• Nothrotherium
• Pronothrotherium
• Thalassocnus

EXTINCTION

                  Along with many other animals, about 10,000 years ago the ground sloths disappears in both of the North and the South America, shortly after the entry of humans. Much evidence suggests human hunting contributed to the extinction of the American megafauna, like that of far northern Asia, Australia, New Zealand and Madagascar. Simultaneous climate change that came with the end of the last Ice Age may have also played a role in some cases. However, the survival of ground sloth on the Antilles until about 5000 years ago (after these islands were finally settled by human),  long after they had died out on the mainland, points toward human activities as the agency of extinction.
                  In Peru and Chile sloths of the genus Thalassocnus adapted to a coastal marine lifestyle beginning in the late Miocene. Initially they just stood in the water, but over a span of 4 million years they eventually evolved into swimming creatures. It is thought that when the Isthmus of Panama, closed about 3 million years ago the water grew colder, perhaps contributing to their extinction by the late Pliocene, The plants these sloths fed on may have grown sparse, or they may have been unable to adapt to the lower water.