page_title: Xenarthra
section_title: Evolutionary relationships
hierarchical_section_title: Xenarthra / Evolutionary relationships
caption_attribution_description: English: Pink fairy armadillos (or pichiciegos) are found in the warm sandy plains of Argentina. These armadillos prefer to burrow in very dry soil. If their burrows are moistened by rainfall, they leave them. These animals often burrow near anthills, so that they can be close to their food source. Pink fairy armadillo generally lives by themselves. The animals stay in their burrrows during the day and feed at night. They are remarkable diggers. Pink fairy armadillos are the smallest members of the armadillo family, measuring only about five to six inches in length. They are also the only armadillo in which the dorsal shell is almost separate from the body. Baby armadillos resemble their parents, but their shells do not completely harden until they are full grown.
context_page_description: Xenarthra is a major clade of placental mammals unique to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Extinct xenarthrans are the glyptodonts, the ground sloths, and the aquatic sloths. Xenarthrans originated in South America during the Paleocene about 59 million years ago. They evolved and diversified extensively in South America during the continent's long period of isolation in the early to mid Cenozoic Era. They spread to the Antilles by the early Miocene and, starting about 3 Mya, spread to Central and North America as part of the Great American Interchange. Nearly all of the formerly abundant megafaunal xenarthrans became extinct at the end of the Pleistocene.
  Xenarthrans share several characteristics not present in other placental mammals, which suggest their ancestors were subterranean diggers for insects. The name Xenarthra derives from the two ancient Greek words ξένος, meaning "strange, unusual", and ἄρθρον, meaning "joint", and refers to their vertebral joints, which have extra articulations that are unlike other mammals. The ischium of the pelvis is also fused to the sacrum of the spine.
context_section_description: Xenarthrans were previously classified alongside the pangolins and aardvarks in the order Edentata (meaning toothless, because the members do not have incisors and lack, or have poorly developed, molars). Subsequently, Edentata was found to be a polyphyletic grouping whose New World and Old World taxa are unrelated, and it was 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 morphology of xenarthrans generally suggests that the anteaters and sloths are more closely related to each other than either is to the armadillos, glyptodonts, and pampatheres; this idea is upheld by molecular studies. Since its conception, Xenarthra has increasingly come to be considered to be of a higher rank than 'order'; some authorities consider it to be a cohort, while others consider it to be a superorder.
  Whatever the rank, Xenarthra is now generally considered to be divided into two orders:
  Cingulata (Latin, "the ones with belts/armor"), the armadillos and the extinct glyptodonts and pampatheres
  Pilosa (Latin, "the ones with fur"), which is subdivided into:
  Vermilingua, the anteaters
  Folivora, the sloths (both tree sloths and the extinct ground sloths). Folivora is also called Tardigrada or Phyllophaga.
  Their relationship to other placental mammals is obscure. Xenarthrans have been defined as most closely related to Afrotheria (in the group Atlantogenata), or to Boreoeutheria (in the group Exafroplacentalia), or to Epitheria (Afrotheria+Boreoeutheria, i.e. as a sister group to all other placental mammals). A comprehensive phylogeny by Goloboff et al. includes xenarthrans as a sister clade of Euarchontoglires within Boreoeutheria (Laurasiatheria+Euarchontoglires). Overall, studies using mitochondrial DNA have tended to group them as a sister clade to Ferrungulata (carnivores+ungulates and cetaceans), while studies using nuclear DNA have identified them as 1) a sister clade to Afrotheria, 2) a sister clade to all placentals except Afrotheria, or 3) a trichotomy (three-way split): Afrotheria, Xenarthra, and everything else (i.e. Boreoeutheria). Among studies that use physical characteristics rather than DNA to look at relationships, a large phenomic analysis of living and fossil mammals suggests placental mammals evolved shortly after the end of the Cretaceous, and first split into Xenarthra and Epitheria (all other placentals).
caption: Pink fairy armadillo (Chlamyphorus truncatus)
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