Xenarthra
Overview
 
The superorder Xenarthra is a group of placental mammals (infraclass Eutheria
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...

), existent today only in the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

 and represented by anteater
Anteater
Anteaters, also known as antbear, are the four mammal species of the suborder Vermilingua commonly known for eating ants and termites. Together with the sloths, they compose the order Pilosa...

s, tree sloth
Sloth
Sloths are the six species of medium-sized mammals belonging to the families Megalonychidae and Bradypodidae , part of the order Pilosa and therefore related to armadillos and anteaters, which sport a similar set of specialized claws.They are arboreal residents of the jungles of Central and South...

s, and armadillo
Armadillo
Armadillos are New World placental mammals, known for having a leathery armor shell. Dasypodidae is the only surviving family in the order Cingulata, part of the superorder Xenarthra along with the anteaters and sloths. The word armadillo is Spanish for "little armored one"...

s. The origins of the order can be traced back as far as the Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...

 (about 60-65 Ma, shortly after the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

) in South America . Xenarthrans developed and diversified extensively in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

 during its long period of isolation, invaded the Antilles
Antilles
The Antilles islands form the greater part of the West Indies in the Caribbean Sea. The Antilles are divided into two major groups: the "Greater Antilles" to the north and west, including the larger islands of Cuba, Jamaica, Hispaniola , and Puerto Rico; and the smaller "Lesser Antilles" on the...

 by the early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...

, and then spread to Central
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

 and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 starting about nine million years ago, as part of the Great American Interchange
Great American Interchange
The Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...

 .
Encyclopedia
The superorder Xenarthra is a group of placental mammals (infraclass Eutheria
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...

), existent today only in the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

 and represented by anteater
Anteater
Anteaters, also known as antbear, are the four mammal species of the suborder Vermilingua commonly known for eating ants and termites. Together with the sloths, they compose the order Pilosa...

s, tree sloth
Sloth
Sloths are the six species of medium-sized mammals belonging to the families Megalonychidae and Bradypodidae , part of the order Pilosa and therefore related to armadillos and anteaters, which sport a similar set of specialized claws.They are arboreal residents of the jungles of Central and South...

s, and armadillo
Armadillo
Armadillos are New World placental mammals, known for having a leathery armor shell. Dasypodidae is the only surviving family in the order Cingulata, part of the superorder Xenarthra along with the anteaters and sloths. The word armadillo is Spanish for "little armored one"...

s. The origins of the order can be traced back as far as the Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...

 (about 60-65 Ma, shortly after the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

) in South America . Xenarthrans developed and diversified extensively in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

 during its long period of isolation, invaded the Antilles
Antilles
The Antilles islands form the greater part of the West Indies in the Caribbean Sea. The Antilles are divided into two major groups: the "Greater Antilles" to the north and west, including the larger islands of Cuba, Jamaica, Hispaniola , and Puerto Rico; and the smaller "Lesser Antilles" on the...

 by the early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...

, and then spread to Central
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

 and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 starting about nine million years ago, as part of the Great American Interchange
Great American Interchange
The Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...

 . Nearly all of the formerly abundant megafauna
Megafauna
In terrestrial zoology, megafauna are "giant", "very large" or "large" animals. The most common thresholds used are or...

l xenarthrans, such as ground sloth
Ground sloth
Ground sloths are a diverse group of extinct sloths, in the mammalian superorder Xenarthra. Their most recent survivors lived in the Antilles, where it has been proposed they may have survived until 1550 CE; however, the youngest AMS radiocarbon date reported is 4190 BP, calibrated to c. 4700 BP...

s, glyptodonts
Glyptodontidae
Glyptodonts were large, more heavily armored relatives of extinct pampatheres and modern armadillos.They first evolved during the Miocene in South America, which remained their center of species diversity...

, and pampatheres
Pampatheriidae
Pampatheridae is an ancient family, now extinct, of large armadillo-like plantigrade armored xenarthrans. They are related to Glyptodontidae, an extinct family of much larger and more heavily armored xenarthrans, as well as to smaller extant armadillos...

 went extinct
Quaternary extinction event
The Quaternary period saw the extinctions of numerous predominantly larger, especially megafaunal, species, many of which occurred during the transition from the Pleistocene to the Holocene epoch. However, the extinction wave did not stop at the end of the Pleistocene, but continued especially on...

 at the end of the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

.

Xenarthrans share several distinctions from those of other placental mammals. The name Xenarthra means "strange joints", and was chosen because their vertebral joints have extra articulations and are unlike those of any other mammals. The males lack external testicle
Testicle
The testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...

s, which are instead placed between the bladder and the rectum. Also, xenarthrans have the lowest metabolic rates among the theria
Theria
Theria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians . The only omitted extant mammal group is the egg-laying monotremes....

ns.

Evolutionary relationships

Xenarthrans were classified in the past together with the pangolin
Pangolin
A pangolin , also scaly anteater or Trenggiling, is a mammal of the order Pholidota. There is only one extant family and one genus of pangolins, comprising eight species. There are also a number of extinct taxa. Pangolins have large keratin scales covering their skin and are the only mammals with...

s and aardvark
Aardvark
The aardvark is a medium-sized, burrowing, nocturnal mammal native to Africa...

s as the order Edentata (meaning toothless, because the members do not have front incisor teeth or molars, or have poorly-developed molars). It was subsequently realized that Edentata was polyphyletic—that it contained unrelated families and was subsequently split up to reflect their true phylogeny. Aardvarks and pangolins are now placed in individual orders, and the new order Xenarthra was erected to group the remaining families (which are all related). The name Xenarthra means "strange joints", and was chosen because their vertebral joints have extra articulations and are unlike those of any other mammals. Because they lack characteristics believed to be present in the common ancestor of other known eutheria
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...

n mammals, some weak morphological evidence suggests that the Xenarthra are outside the Epitheria
Epitheria
Epitherians comprise all the placental mammals except the Xenarthra. They are primarily characterized by having a stirrup-shaped stapes in the middle ear, which allows for passage of a blood vessel. This is in contrast to the column-shaped stapes found in marsupials, monotremes, and xenarthrans...

, which contains all other known eutherians today. Some workers have even placed xenarthrans outside of placentals as a separate group Paratheria
Paratheria (mammals)
Paratheria is an obsolete term used for a group that included at least the xenarthran mammals. It was proposed by Oldfield Thomas in 1887 to set apart the sloths, anteaters, armadillos, and pangolins, usually classified as placentals, from both marsupial and placental mammals, an arrangement that...

.

The morphology of xenarthrans generally suggests that the anteaters and sloths are closest together within Xenarthra, which is upheld by molecular studies. The order Xenarthra is more and more often divided into two orders: Pilosa, containing the Vermilingua (anteaters) and Folivora (sloths; previously known as Tardigrada or Phyllophaga), and the separate order Cingulata (armadillos). Xenarthra now has the rank of cohort or super-order. The Xenarthra are part of the super-cohort Atlantogenata
Atlantogenata
Atlantogenata is a proposed clade of mammals containing the cohorts or super-orders Afrotheria, Xenarthra and Meridiungulata. These groups originated and radiated in the South American and African continents, presumably in the Cretaceous. Together with Boreoeutheria it makes up Eutheria...

.

Xenarthra may be most closely related to either Afrotheria
Afrotheria
Afrotheria is a clade of mammals, the living members of which belong to groups from Africa or of African origin: golden moles, sengis , tenrecs, aardvarks, hyraxes, elephants and sea cows. The common ancestry of these animals was not recognized until the late 1990s...

 (in the group Atlantogenata
Atlantogenata
Atlantogenata is a proposed clade of mammals containing the cohorts or super-orders Afrotheria, Xenarthra and Meridiungulata. These groups originated and radiated in the South American and African continents, presumably in the Cretaceous. Together with Boreoeutheria it makes up Eutheria...

), or Epitheria
Epitheria
Epitherians comprise all the placental mammals except the Xenarthra. They are primarily characterized by having a stirrup-shaped stapes in the middle ear, which allows for passage of a blood vessel. This is in contrast to the column-shaped stapes found in marsupials, monotremes, and xenarthrans...

 (comprising Afrotheria and Boreoeutheria). In other words it may be nested within Eutheria or it may be the basal extant group. A comprehensive phylogeny by Goloboff et al. includes xenarthrans as a sister clade of Boreoeutheria
Boreoeutheria
Boreoeutheria is a clade of placental mammals that is composed of the sister taxa Laurasiatheria and Euarchontoglires...

 (Euarchontoglires
Euarchontoglires
Euarchontoglires is a clade of mammals, the living members of which are rodents, lagomorphs, treeshrews, colugos and primates .-Evolutionary relationships:...

+Laurasiatheria
Laurasiatheria
Laurasiatheria is a large group of placental mammals believed to have originated on the northern supercontinent of Laurasia. It includes shrews, hedgehogs, pangolins, bats, whales, most hoofed mammals, and carnivorans, among others....

) (in the Exafroplacentalia
Exafroplacentalia
Exafroplacentalia or Notolegia is a subcohort selected in 2001 on the basis of molecular researches.-Exafroplacentalia:Exafroplacentalia places Xenarthra as a sister group to the magnorder Boreoeutheria , thus making Afrotheria a primitive group of placental mammals...

=Notolegia).

Classification

SUPERORDER XENARTHRA
  • Order Cingulata

    • Family Dasypodidae: armadillos
      • Pink Fairy Armadillo
        Pink Fairy Armadillo
        The pink fairy armadillo or pichiciego is the smallest species of armadillo...

        , Chlamyphorus truncatus
      • Northern Naked-tailed Armadillo
        Northern Naked-tailed Armadillo
        The Northern Naked-tailed Armadillo is a species of armadillo. It is found from Chiapas in southern Mexico to western Colombia, northwestern Ecuador and northwestern Venezuela, at altitudes from sea level to 3000 m...

        , Cabassous centralis
      • Chacoan Naked-tailed Armadillo
        Chacoan Naked-tailed Armadillo
        The Chacoan Naked-tailed Armadillo is a species of armadillo in the Dasypodidae family. It is found in Argentina, Paraguay, and possibly Brazil. Its natural habitats are subtropical or tropical dry forests and subtropical or tropical dry shrubland. It is threatened by habitat loss....

        , Cabassous chacoensis
      • Southern Naked-tailed Armadillo
        Southern Naked-tailed Armadillo
        The Southern Naked-tailed Armadillo, Cabassous unicinctus, is a small species of armadillo from South America. It is found in Colombia, Ecuador, Venezuela, Peru, Bolivia and Brazil....

        , Cabassous unicinctus
      • Greater Naked-tailed Armadillo
        Greater Naked-tailed Armadillo
        The Greater Naked-tailed Armadillo, Cabassous tatouay, is an armadillo species from South America. It is found in Argentina, Bolivia, Brazil, Paraguay, Peru and Uruguay.-References:*...

        , Cabassous tatouay
      • Screaming Hairy Armadillo
        Screaming Hairy Armadillo
        The Screaming Hairy Armadillo is a species of armadillo also known as the Small Screaming Armadillo, Crying Armadillo or the Small Hairy Armadillo. It is a burrowing armadillo found in the central and southern parts of South America...

        , Chaetophractus vellerosus
      • Big Hairy Armadillo
        Big Hairy Armadillo
        Chaetophractus villosus, commonly called the Big Hairy Armadillo is one of the largest and most numerous armadillos in South America. It lives from sea level to altitudes of up to 1,300 meters across the southern portion of South America and can be found in grasslands, forests, savannahs, and has...

        , Chaetophractus villosus
      • Andean Hairy Armadillo
        Andean Hairy Armadillo
        The Andean Hairy Armadillo is an armadillo present in Bolivia, in the region of the Puna, the departments of Oruro, La Paz, and Cochabamba . Nowark describes it as distributed in Bolivia and northern Chile. A recent publication of Pacheco et al. also locates the species in Peru...

        , Chaetophractus nationi
      • Nine-banded Armadillo
        Nine-banded Armadillo
        The nine-banded armadillo , or the nine-banded, long-nosed armadillo, is a species of armadillo found in North, Central, and South America, making it the most widespread of the armadillos...

         or Long-nosed Armadillo, Dasypus novemcinctus
      • Seven-banded Armadillo
        Seven-banded Armadillo
        Seven-banded, long-nosed armadillo or just seven-banded armadillo, Dasypus septemcinctus, is a species of armadillo from South America...

        , Dasypus septemcinctus
      • Southern Long-nosed Armadillo
        Southern Long-nosed Armadillo
        The Southern Long-nosed Armadillo, Dasypus hybridus, is an armadillo species from South America. It is found in Argentina, Brazil, Paraguay and Uruguay.-References:*...

        , Dasypus hybridus
      • Llanos Long-nosed Armadillo
        Llanos Long-nosed Armadillo
        The Llanos Long-nosed Armadillo is a species of armadillo in the Dasypodidae family. It is endemic to Colombia and Venezuela. The species is very closely related to the Nine-banded Armadillo and the Greater Long-nosed Armadillo. It has very little hair and can weigh up to 22 pounds , and can...

        , Dasypus sabanicola
      • Great Long-nosed Armadillo, Dasypus kappleri
      • Hairy Long-nosed Armadillo
        Hairy Long-nosed Armadillo
        The hairy long-nosed armadillo is a species of armadillo in the family Dasypodidae. It is endemic to Peru. Its natural habitats are subtropical or tropical, moist, lowland forests and subtropical or tropical, moist montanes. It is threatened by habitat loss....

        , Dasypus pilosus
      • Six-banded Armadillo
        Six-banded Armadillo
        The Six-banded Armadillo , also known as the Yellow Armadillo, is a species of armadillo from South America. It is found in Argentina, Bolivia, Brazil, Uruguay, Paraguay and isolated populations in Suriname . Its body is usually yellowish in color, sometimes tan or light reddish-brown...

         or Yellow Armadillo, Euphractus sexcinctus
      • Giant Armadillo
        Giant Armadillo
        The giant armadillo , colloquially tatou, ocarro, tatu-canastra or tatú carreta, is the largest living species of armadillo...

        , Priodontes maximus
      • Southern Three-banded Armadillo
        Southern Three-banded Armadillo
        The Southern Three-banded Armadillo , also called the La Plata Three-Banded Armadillo, is an armadillo species from South America...

        , Tolypeutes matacus
      • Brazilian Three-banded Armadillo
        Brazilian Three-banded Armadillo
        The Brazilian Three-banded Armadillo is an armadillo species endemic to Brazil. It is one of only two species of armadillo that can roll into a ball...

        , Tolypeutes tricinctus
      • Pichi
        Pichi
        The Pichi or Dwarf Armadillo is a small armadillo that is the only member the genus Zaedyus. The range of the Pichi is from central and southern Argentina , west to the Andean grasslands of Chile and south to the Strait of Magellan.Its body is approximately long with a tail of 4-6 inches...

         or Dwarf Armadillo, Zaedyus pichiy
    • Family †Glyptodontidae
      Glyptodontidae
      Glyptodonts were large, more heavily armored relatives of extinct pampatheres and modern armadillos.They first evolved during the Miocene in South America, which remained their center of species diversity...

      : glyptodonts
    • Family †Pampatheriidae
      Pampatheriidae
      Pampatheridae is an ancient family, now extinct, of large armadillo-like plantigrade armored xenarthrans. They are related to Glyptodontidae, an extinct family of much larger and more heavily armored xenarthrans, as well as to smaller extant armadillos...

      : pampatheres
  • Order Pilosa
    Pilosa
    The order Pilosa is a group of placental mammals, extant today only in the Americas. It includes the anteaters and sloths, including the recently extinct ground sloths....

    • Suborder Folivora
      • Family Bradypodidae: three-toed sloths
        • Pygmy Three-toed Sloth
          Pygmy Three-toed Sloth
          The Pygmy Three-toed Sloth is a three-toed sloth. It is endemic to Isla Escudo de Veraguas, an island off the coast of Panama, which separated from the mainland nearly 8900 years ago. The species is thought to have originated from isolation of individuals from the mainland population of Bradypus...

          , Bradypus pygmaeus
        • Brown-throated Three-toed Sloth
          Brown-throated Three-toed Sloth
          The brown-throated sloth is a species of three-toed sloth. It is the most common of the four species of three-toed sloth, and is found in the forests of South and Central America.-Description:...

          , Bradypus variegatus
        • Pale-throated Three-toed Sloth
          Pale-throated Three-toed Sloth
          The Pale-throated sloth is a species of three-toed sloth that inhabits tropical rainforests in northern South America. It is similar in appearance to, and often confused with, the brown-throated sloth, which has a much wider distribution...

          , Bradypus tridactylus
        • Maned Three-toed Sloth
          Maned Three-toed Sloth
          The maned sloth , also known as the ai , is a three-toed sloth that lives only in Brazil. It is one of only four species of three-toed sloth.-Distribution and habitat:...

          , Bradypus torquatus
      • Family Megalonychidae
        Megalonychidae
        Megalonychidae is a group of sloths including the extinct Megalonyx and the living two toed sloths. Megalonychids first appeared in the early Oligocene, about 35 million years ago, in southern Argentina , and spread as far as the Antilles by the early Miocene...

        : two-toed sloths and extinct megalonychid ground sloths
        • Hoffman's Two-toed Sloth, Choloepus hoffmanni
        • Linnaeus's Two-toed Sloth
          Linnaeus's Two-toed Sloth
          Linnaeus's two-toed sloth , also known as the Southern two-toed sloth or unau, is a species of sloth from South America, found in Venezuela, the Guyanas, Colombia, Ecuador, Peru and Brazil north of the Amazon River....

           or Southern Two-toed Sloth, Choloepus didactylus
      • Family †Megatheriidae
        Megatheriidae
        Megatheriidae is a family of extinct ground sloths that lived from approximately 23 mya—11,000 years ago, existing for approximately .Megatheriids appeared later in the Oligocene, some 30 million years ago, also in South America. The group includes the heavily-built Megatherium and Eremotherium...

        : megatheriid ground sloths
      • Family †Mylodontidae
        Mylodontidae
        Mylodontidae is a family of extinct mammals within the order of Pilosa and suborder Folivora living from approximately 23 mya—11,000 years ago, existing for approximately . This family of ground sloths is related to the other families of extinct ground sloths, being the Megatheriidae, the...

        : mylodontid ground sloths
      • Family †Orophodontidae
        Orophodontidae
        Orophodontidae is a family of extinct ground sloths within the order of Pilosa and suborder Folivora. The name is often disused with genus members reassigned....

        : orophodontid ground sloths
    • Suborder Vermilingua
      • Family Cyclopedidae
        Cyclopedidae
        Cyclopedidae is a family of anteaters that includes the silky anteater and its extinct relatives....

        : silky anteaters
        • Silky Anteater
          Silky Anteater
          The Silky Anteater or Pygmy Anteater is a species of anteater from Central and South America, ranging from extreme southern Mexico south to Brazil Delta Amacuro Venezuela and possibly Paraguay...

          , Cyclopes didactylus
      • Family Myrmecophagidae
        Myrmecophagidae
        Myrmecophagidae is a family of anteaters, the name being derived from the Ancient Greek words for 'ant' and 'eat' . Myrmecophagids are native to Central and South America, from southern Mexico to northern Argentina. There are 2 genera and 3 species in the family, consisting of the Giant Anteater,...

        : anteaters
        • Giant Anteater
          Giant Anteater
          The Giant Anteater, Myrmecophaga tridactyla, is the largest species of anteater. It is the only species in the genus Myrmecophaga. It is found in Central and South America from Honduras to northern Argentina...

          , Myrmecophaga tridactyla
        • Northern Tamandua
          Northern Tamandua
          The northern tamandua is a species of tamandua, a small anteater in the family Myrmecophagidae. They live in tropical and subtropical forests from southern Mexico, through Central America, and to the edge of the northern Andes....

          , Tamandua mexicana
        • Southern Tamandua
          Southern Tamandua
          The southern tamandua, also called a collared anteater, or lesser anteater , is a species of anteater from South America. It is a solitary animal, found in many habitats from mature to highly disturbed secondary forests and arid savannas. It feeds on ants, termites and bees...

          , Tamandua tetradactyla

External links

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