SLOTHS

Cards (122)

  • Sloths are a Neotropical group of xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths
  • The common ancestor of 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
  • Ancient sloths were mostly terrestrial, and some reached sizes that rival those of elephants, as 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
  • The nothrotheriid Thalassocnus of the west coast of South America became adapted to a semiaquatic and, eventually, perhaps fully aquatic marine lifestyle
  • 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
  • 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
  • The 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
  • Much of the morphological evidence collected to support the hypothesis of diphyly has been based on the structure of the inner ear
  • 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
  • Folivora
    Sloth family phylogenetic tree
  • 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
  • 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
  • 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
  • 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 the manatees, with six
  • Sloths
    Have colour vision but have poor visual acuity, and have poor hearing
  • Sloths 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 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 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
  • Sloth fur is a small ecosystem of its own, hosting many species of commensal and parasitic arthropods
  • Arthropods associated with sloths

    • Biting and blood-sucking flies such as mosquitoes and sandflies
    • Triatomine bugs
    • Lice
    • Ticks
    • Mites
  • Sloths have a highly specific community of commensal beetles, mites and moths
  • Sloths benefit from their relationship with moths because the moths are responsible for fertilizing algae on the sloth, which provides them with nutrients
  • Sloths
    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, while most other mammals have a muscle mass that makes up 40 to 45 percent of their total body weight
  • Sloths
    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