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Xenarthra - Wikipedia XenarthraFrom Wikipedia, the free encyclopediaSuperorder of mammals that diversified in South America
Xenarthrans
Temporal range: Paleocene  –Recent, 59–0  Ma
Xenarthra.jpg
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Placentalia
Superorder: Xenarthra
Cope , 1889
Orders and suborders


See text for more details

Xenarthra ( Latin , from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a superorder of placental mammals found in the Americas . It currently consists of 31 extant species, made up of anteaters , tree sloths , and armadillo s . 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, such as ground sloths , glyptodonts and pampatheres , became extinct at the end of the Pleistocene .

Xenarthrans share several characteristics not present in other placental mammals and are often considered to be among the most primitive order of placental mammals. The name Xenarthra, which means "strange joints", was chosen because their vertebral joints have extra articulations unlike other mammals. This trait is referred to as "xenarthry". Also, unlike other mammals, the ischium and sacrum are fused. The males have internal testicles , which are located between the bladder and the rectum. Xenarthrans have been determined to have single-color vision . Furthermore, xenarthrans have the lowest metabolic rates among the therians . They also seem to lack a functional pineal gland .

ContentsEvolutionary relationships[ edit ] Pink fairy armadillo (Chlamyphorus truncatus)

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 name Xenarthra means "strange joints", and was chosen because their vertebral joints have extra articulations and are unlike those of any other mammals. The morphology of xenarthrans generally suggests that the anteaters and sloths are more closely related to each other than either is to the armadillos; this 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 , which contains the armadillos; and Pilosa , which contains the Vermilingua (anteaters) and Folivora (sloths; previously known as Tardigrada or Phyllophaga).

Xenarthra may be most closely related to either Afrotheria (in the group Atlantogenata ), Boreoeutheria (in the group Exafroplacentalia ), or Epitheria (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 Euarchontoglires within Boreoeutheria ( Laurasiatheria + Euarchontoglires ).

Phylogeny[ edit ]

Below is a recent simplified phylogeny of the xenarthran families based on Slater et al. (2016) and Delsuc et al. (2016). The dagger symbol, "†", denotes extinct groups.

Xenarthra
Cingulata

Dasypodidae

Pampatheriidae

Chlamyphoridae

Pilosa
Vermilingua

Cyclopedidae

Myrmecophagidae

Folivora

Megatheriidae

Nothrotheriidae

Bradypodidae

Mylodontidae

Megalonychidae

Classification[ edit ] Screaming hairy armadillo Southern three-banded armadillo Brown-throated three-toed sloth Giant anteater Southern tamandua juvenile

XENARTHRA

Order Cingulata Family Chlamyphoridae : armadillos and glyptodonts Greater fairy armadillo , Calyptophractus retusus Pink fairy armadillo , Chlamyphorus truncatus Northern naked-tailed armadillo , Cabassous centralis Chacoan naked-tailed armadillo , Cabassous chacoensis Southern naked-tailed armadillo , Cabassous unicinctus Greater naked-tailed armadillo , Cabassous tatouay Screaming hairy armadillo , Chaetophractus vellerosus Big hairy armadillo , Chaetophractus villosus Andean hairy armadillo , Chaetophractus nationi Six-banded armadillo or yellow armadillo, Euphractus sexcinctus Giant armadillo , Priodontes maximus Southern three-banded armadillo , Tolypeutes matacus Brazilian three-banded armadillo , Tolypeutes tricinctus Pichi or dwarf armadillo, Zaedyus pichiySubfamily † Glyptodontinae : glyptodontsFamily Dasypodidae : long-nosed armadillos Nine-banded armadillo or long-nosed armadillo, Dasypus novemcinctus Seven-banded armadillo , Dasypus septemcinctus Southern long-nosed armadillo , Dasypus hybridus Llanos long-nosed armadillo , Dasypus sabanicola Great long-nosed armadillo , Dasypus kappleri Hairy long-nosed armadillo , Dasypus pilosus Yepes's mulita , Dasypus yepesiFamily † Pampatheriidae : pampatheresOrder Pilosa Suborder Folivora : sloths Family Bradypodidae : three-toed sloths Pygmy three-toed sloth , Bradypus pygmaeus Brown-throated three-toed sloth , Bradypus variegatus Pale-throated three-toed sloth , Bradypus tridactylus Maned three-toed sloth , Bradypus torquatusFamily Megalonychidae : two-toed sloths and extinct megalonychid ground sloths Hoffman's two-toed sloth , Choloepus hoffmanni Linnaeus's two-toed sloth or southern two-toed sloth, Choloepus didactylusFamily † Megatheriidae : megatheriid ground slothsFamily † Mylodontidae : mylodontid ground slothsFamily † Nothrotheriidae : nothrotheriid ground sloths and aquatic slothsSuborder Vermilingua : anteaters Family Cyclopedidae : silky anteaters Silky anteater , Cyclopes didactylusFamily Myrmecophagidae : anteaters Giant anteater , Myrmecophaga tridactyla Northern tamandua , Tamandua mexicana Southern tamandua , Tamandua tetradactylaCharacteristics[ edit ]

Xenarthrans share several characteristics not present in other placental mammals, and are often considered to be among the most primitive order of placental mammals. [ citation needed ]

Dentition[ edit ]

The dentition of Xenarthrans differs from most placentals as it is either significantly reduced and highly modified, or entirely absent. Currently, no extant or extinct Xenarthrans have been found to have the standard mammalian dental formula or crown morphology derived from the ancient tribosphenic pattern.

Spine[ edit ]

The name Xenarthra, which means "strange joints", was chosen because their vertebral joints have extra articulations unlike other mammals. This trait is referred to as "xenarthry". Also, unlike other mammals, the ischium and sacrum are fused.

Vision[ edit ]

Xenarthrans have been determined to have single-color vision. Through PCR analysis, it was discovered that a mutation in a stem Xenarthran led to long-wavelength sensitive-con (LWS) monochromacy (single color vision) common in nocturnal, aquatic and subterranean mammals. Further losses led to rod monochromancy in a stem cingulate and a stem pilosan pointing to a subterranean ancestry.

Metabolism and anomalous organs[ edit ]

Xenarthrans have the lowest metabolic rates among the therians . Furthermore, they seem to lack a functional pineal gland .

The males have internal testicles , which are located between the bladder and the rectum.

References[ edit ]The biology of the Xenarthra. Vizcaíno, Sergio F., Loughry, W. J. Gainesville: University Press of Florida. 2008. ISBN   978-0-8130-3718-9 . OCLC   741613153 .CS1 maint: others ( link ) O'Leary, M. A.; Bloch, J. I.; Flynn, J. J.; Gaudin, T. J.; Giallombardo, A.; Giannini, N. P.; Cirranello, A. L. (2013). "The placental mammal ancestor and the post–K-Pg radiation of placentals" . Science. 339 (6120): 662–667. Bibcode : 2013Sci...339..662O . doi : 10.1126/science.1229237 . hdl : 11336/7302 . PMID   23393258 .Woodburne, Michael O. (2010). "The Great American Biotic Interchange: Dispersals, Tectonics, Climate, Sea Level and Holding Pens" . Journal of Mammalian Evolution. 17 (4): 245–264. doi : 10.1007/s10914-010-9144-8 . PMC   2987556 . PMID   21125025 .^ Delsuc, Frédéric; Catzteflis, François M.; Stanhope, Michael J.; Douzery, Emmanuel J. P. (August 2001). "The evolution of armadillos, anteaters and sloths depicted by nuclear and mitochondrial phylogenies: implications for the status of the enigmatic fossil Eurotamandua " (PDF). Proc. R. Soc. Lond. B. 268 (1476): 1605–15. doi : 10.1098/rspb.2001.1702 . PMC   1088784 . PMID   11487408 .Kleisner, K; Ivell, R; Flegr, J (2010). "The evolutionary history of testicular externalization and the origin of the scrotum". Journal of Biosciences. 35 (1): 27–37. doi : 10.1007/s12038-010-0005-7 . PMID   20413907 .Elgar, M. A.; Harvey, P. H. (1987). "Basal Metabolic Rates in Mammals: Allometry, Phylogeny and Ecology". Functional Ecology. 1 (1): 25–36. doi : 10.2307/2389354 . JSTOR   2389354 .Lovegrove, Barry G. (2000). "The Zoogeography of Mammalian Basal Metabolic Rate". The American Naturalist. 156 (2): 201–19. doi : 10.1086/303383 . JSTOR   3079219 . PMID   10856202 . The Pineal Gland and its Endocrine Role McKenna, M.C.; Bell, S.K. (1997). Classification of Mammals Above the Species Level. New York: Columbia University Press. p. 93. ISBN   978-0-231-11013-6 . OCLC   37345734 .Murphy, W. J.; Pringle, T. H.; Crider, T. A.; Springer, M. S.; Miller, W. (2007). "Using genomic data to unravel the root of the placental mammal phylogeny" . Genome Research. 17 (4): 413–21. doi : 10.1101/gr.5918807 . PMC   1832088 . PMID   17322288 .Kriegs, Jan Ole; Churakov, Gennady; Kiefmann, Martin; Jordan, Ursula; Brosius, Jürgen; Schmitz, Jürgen (2006). "Retroposed Elements as Archives for the Evolutionary History of Placental Mammals" . PLoS Biology. 4 (4): e91. doi : 10.1371/journal.pbio.0040091 . PMC   1395351 . PMID   16515367 .Goloboff, Pablo A.; Catalano, Santiago A.; Marcos Mirande, J.; Szumik, Claudia A.; Salvador Arias, J.; Källersjö, Mari; Farris, James S. (2009). "Phylogenetic analysis of 73 060 taxa corroborates major eukaryotic groups". Cladistics. 25 (3): 211–30. doi : 10.1111/j.1096-0031.2009.00255.x .Slater, G., Cui, P., Forasiepi, A. M., Lenz, D., Tsangaras, K., Voirin, B., ... & Greenwood, A. D. (2016). Evolutionary relationships among extinct and extant sloths: the evidence of mitogenomes and retroviruses. Genome Biology and Evolution, evw023.Delsuc, F., Gibb, G. C., Kuch, M., Billet, G., Hautier, L., Southon, J., ... & Poinar, H. N. (2016). The phylogenetic affinities of the extinct glyptodonts. Current Biology, 26(4), R155-R156.Vizcaíno, Sergio F. (2009). "The teeth of the "toothless": novelties and key innovations in the evolution of xenarthrans (Mammalia, Xenarthra)". Paleobiology. 35 (3): 343–366. doi : 10.1666/0094-8373-35.3.343 . ISSN   0094-8373 .Gaudin, Timothy J.; Croft, Darin A. (2015-06-24). "Paleogene Xenarthra and the evolution of South American mammals". Journal of Mammalogy. 96 (4): 622–634. doi : 10.1093/jmammal/gyv073 . ISSN   0022-2372 .^ Emerling, Christopher A.; Springer, Mark S. (2015-02-07). "Genomic evidence for rod monochromacy in sloths and armadillos suggests early subterranean history for Xenarthra" . Proceedings of the Royal Society B: Biological Sciences. 282 (1800): 20142192. doi : 10.1098/rspb.2014.2192 . ISSN   0962-8452 . PMC   4298209 . PMID   25540280 .Elgar, M. A.; Harvey, P. H. (1987). "Basal Metabolic Rates in Mammals: Allometry, Phylogeny and Ecology". Functional Ecology. 1 (1): 25–36. doi : 10.2307/2389354 . JSTOR   2389354 .Lovegrove, Barry G. (2000). "The Zoogeography of Mammalian Basal Metabolic Rate". The American Naturalist. 156 (2): 201–219. doi : 10.1086/303383 . JSTOR   3079219 . PMID   10856202 .Axelrod, J. (December 2013). The Pineal Gland and its Endocrine Role . ISBN   9781475714517 – via Google Books.[ full citation needed ]Kleisner, K.; Ivell, R.; Flegr, J. (2010). "The evolutionary history of testicular externalization and the origin of the scrotum". Journal of Biosciences. 35 (1): 27–37. doi : 10.1007/s12038-010-0005-7 . PMID   20413907 .External links[ edit ] Wildman, Derek E.; Chen, Caoyi; Erez, Offer; Grossman, Lawrence I.; Goodman, Morris; Romero, Roberto (2006). "Evolution of the mammalian placenta revealed by phylogenetic analysis" . Proceedings of the National Academy of Sciences. 103 (9): 3203–3208. Bibcode : 2006PNAS..103.3203W . doi : 10.1073/pnas.0511344103 . JSTOR   30048561 . PMC   1413940 . PMID   16492730 . "Armadillos: Biology, Ecology and Images" . Armadillo Online. 1995. Retrieved 19 December 2017. 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