| 词条 | Xenarthra |
| 释义 |
| name = Xenarthrans | fossil_range = Paleocene –Recent, {{fossil range|59|0}} | image = Choloepus hoffmanni (Puerto Viejo, CR) crop.jpg | image_upright = 1.3 | image_caption = Hoffmann's two-toed sloth (Choloepus hoffmanni) | taxon = Xenarthra | authority = Cope, 1889 | subdivision_ranks = Orders and suborders | subdivision =
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 anteaters, tree sloths, and armadillos. Xenarthrans originated in South America during the Paleocene about 59 million years ago.[1] 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.[2] 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.[3] The males have internal testicles, which are located between the bladder and the rectum.[4] Xenarthrans have been determined to have single-color vision. Furthermore, xenarthrans have the lowest metabolic rates among the therians.[5][6] They also seem to lack a functional pineal gland.[7] Evolutionary relationshipsXenarthrans 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).[8] Xenarthra may be most closely related to either Afrotheria[9] (in the group Atlantogenata), Boreoeutheria (in the group Exafroplacentalia), or Epitheria[10] (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.[11] includes xenarthrans as a sister clade of Euarchontoglires within Boreoeutheria (Laurasiatheria+Euarchontoglires). PhylogenyBelow is a recent simplified phylogeny of the xenarthran families based on Slater et al. (2016)[12] and Delsuc et al. (2016).[13] The dagger symbol, "†", denotes extinct groups. {{clade|style=font-size:100%|label1=Xenarthra |1={{Clade |label1=Cingulata |1={{Clade |1=Dasypodidae |label2= |2={{Clade |1=†Pampatheriidae |2=Chlamyphoridae |label2=Pilosa |2={{Clade |label1=Vermilingua |1={{Clade |1=Cyclopedidae |2=Myrmecophagidae |label2=Folivora |2={{Clade |label1= |1={{Clade |1=†Megatheriidae |label1= |2={{Clade |1=†Nothrotheriidae |2=Bradypodidae }} }} |2={{Clade |label1= |1={{Clade |1=†Mylodontidae |2=Megalonychidae }} }} }} }} }} }} ClassificationXENARTHRA
CharacteristicsXenarthrans 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.[14] The males have internal testicles, which are located between the bladder and the rectum.[15] 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.[16] Further losses led to rod monochromancy in a stem cingulate and a stem pilosan pointing to a subterranean ancestry.[16] Furthermore, xenarthrans have the lowest metabolic rates among the therians.[17][18] They also seem to lack a functional pineal gland.[19] ==References== 1. ^{{cite journal | last1 = O'Leary | first1 = M. A. | last2 = Bloch | first2 = J. I. | last3 = Flynn | first3 = J. J. | last4 = Gaudin | first4 = T. J. | last5 = Giallombardo | first5 = A. | last6 = Giannini | first6 = N. P. | last7 = Cirranello | first7 = A. L. | year = 2013 | title = The placental mammal ancestor and the post–K-Pg radiation of placentals | url = | journal = Science | volume = 339 | issue = 6120| pages = 662–667 | doi=10.1126/science.1229237 | pmid=23393258| hdl = 11336/7302 | bibcode = 2013Sci...339..662O }} 2. ^{{cite journal |doi=10.1007/s10914-010-9144-8 |title=The Great American Biotic Interchange: Dispersals, Tectonics, Climate, Sea Level and Holding Pens |year=2010 |last1=Woodburne |first1=Michael O. |journal=Journal of Mammalian Evolution |volume=17 |issue=4 |pages=245–264 |pmid=21125025 |pmc=2987556}} 3. ^{{Cite journal | last1 = Delsuc | first1 = Frédéric | last2 = Catzteflis | first2 = François M. | last3 = Stanhope | first3 = Michael J. | last4 = Douzery | first4 = Emmanuel J. P. | title = The evolution of armadillos, anteaters and sloths depicted by nuclear and mitochondrial phylogenies: implications for the status of the enigmatic fossil Eurotamandua | journal = Proc. R. Soc. Lond. B |date=August 2001 | volume = 268 | issue = 1476 | pages = 1605–15 | url = http://fdelsuc.perso.neuf.fr/fd_files/Delsuc-ProcRSocB01.pdf | doi = 10.1098/rspb.2001.1702 | pmc = 1088784 | pmid=11487408}} 4. ^{{cite journal |pmid=20413907 |year=2010 |last1=Kleisner |first1=K |last2=Ivell |first2=R |last3=Flegr |first3=J |title=The evolutionary history of testicular externalization and the origin of the scrotum |volume=35 |issue=1 |pages=27–37 |journal=Journal of Biosciences |doi=10.1007/s12038-010-0005-7}} 5. ^{{cite journal |first1=M. A. |last1=Elgar |first2=P. H. |last2=Harvey |year=1987 |title=Basal Metabolic Rates in Mammals: Allometry, Phylogeny and Ecology |journal=Functional Ecology |volume=1 |issue=1 |pages=25–36 |jstor=2389354 |doi=10.2307/2389354}} 6. ^{{cite journal |first1=Barry G. |last1=Lovegrove |year=2000 |title=The Zoogeography of Mammalian Basal Metabolic Rate |journal=The American Naturalist |volume=156 |issue=2 |pages=201–19 |doi=10.1086/303383 |pmid=10856202 |jstor=3079219}} 7. ^[https://books.google.no/books?id=VH7SBwAAQBAJ&pg=PA62&dq=pineal+regularly+present+Xenarthra&hl=no&sa=X&ved=0ahUKEwiCvYzVlp7aAhWLVywKHascC5oQ6AEIKDAA#v=onepage&q=pineal%20regularly%20present%20Xenarthra&f=false The Pineal Gland and its Endocrine Role] 8. ^{{cite book | last1 = McKenna | first1 = M.C. | last2 = Bell | first2 = S.K. | title = Classification of Mammals Above the Species Level | publisher = Columbia University Press | location = New York | isbn = 978-0-231-11013-6 | oclc = 37345734| year = 1997 | pages = 93}} 9. ^{{cite journal |doi=10.1101/gr.5918807 |title=Using genomic data to unravel the root of the placental mammal phylogeny |year=2007 |last1=Murphy |first1=W. J. |last2=Pringle |first2=T. H. |last3=Crider |first3=T. A. |last4=Springer |first4=M. S. |last5=Miller |first5=W. |journal=Genome Research |volume=17 |issue=4 |pages=413–21 |pmid=17322288 |pmc=1832088}} 10. ^{{cite journal |doi=10.1371/journal.pbio.0040091 |title=Retroposed Elements as Archives for the Evolutionary History of Placental Mammals |year=2006 |last1=Kriegs |first1=Jan Ole |last2=Churakov |first2=Gennady |last3=Kiefmann |first3=Martin |last4=Jordan |first4=Ursula |last5=Brosius |first5=Jürgen |last6=Schmitz |first6=Jürgen |journal=PLoS Biology |volume=4 |issue=4 |pages=e91 |pmid=16515367 |pmc=1395351}} 11. ^{{cite journal |doi=10.1111/j.1096-0031.2009.00255.x |title=Phylogenetic analysis of 73 060 taxa corroborates major eukaryotic groups |year=2009 |last1=Goloboff |first1=Pablo A. |last2=Catalano |first2=Santiago A. |last3=Marcos Mirande |first3=J. |last4=Szumik |first4=Claudia A. |last5=Salvador Arias |first5=J. |last6=Källersjö |first6=Mari |last7=Farris |first7=James S. |journal=Cladistics |volume=25 |issue=3 |pages=211–30}} 12. ^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. 13. ^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. 14. ^{{Cite journal | last1 = Delsuc | first1 = Frédéric | last2 = Catzteflis | first2 = François M. | last3 = Stanhope | first3 = Michael J. | last4 = Douzery | first4 = Emmanuel J. P. | title = The evolution of armadillos, anteaters and sloths depicted by nuclear and mitochondrial phylogenies: implications for the status of the enigmatic fossil Eurotamandua | journal = Proc. R. Soc. Lond. B |date=August 2001 | volume = 268 | issue = 1476 | pages = 1605–15 | url = http://fdelsuc.perso.neuf.fr/fd_files/Delsuc-ProcRSocB01.pdf | doi = 10.1098/rspb.2001.1702 | pmc = 1088784 | pmid=11487408}} 15. ^{{cite journal |pmid=20413907 |year=2010 |last1=Kleisner |first1=K |last2=Ivell |first2=R |last3=Flegr |first3=J |title=The evolutionary history of testicular externalization and the origin of the scrotum |volume=35 |issue=1 |pages=27–37 |journal=Journal of Biosciences |doi=10.1007/s12038-010-0005-7}} 16. ^1 {{Cite journal|last=Emerling|first=Christopher A.|last2=Springer|first2=Mark S.|date=2015-02-07|title=Genomic evidence for rod monochromacy in sloths and armadillos suggests early subterranean history for Xenarthra|journal=Proceedings of the Royal Society B: Biological Sciences|volume=282|issue=1800|pages=20142192|doi=10.1098/rspb.2014.2192|issn=0962-8452|pmc=4298209|pmid=25540280}} 17. ^{{cite journal |first1=M. A. |last1=Elgar |first2=P. H. |last2=Harvey |year=1987 |title=Basal Metabolic Rates in Mammals: Allometry, Phylogeny and Ecology |journal=Functional Ecology |volume=1 |issue=1 |pages=25–36 |jstor=2389354 |doi=10.2307/2389354}} 18. ^{{cite journal |first1=Barry G. |last1=Lovegrove |year=2000 |title=The Zoogeography of Mammalian Basal Metabolic Rate |journal=The American Naturalist |volume=156 |issue=2 |pages=201–19 |doi=10.1086/303383 |pmid=10856202 |jstor=3079219}} 19. ^[https://books.google.no/books?id=VH7SBwAAQBAJ&pg=PA62&dq=pineal+regularly+present+Xenarthra&hl=no&sa=X&ved=0ahUKEwiCvYzVlp7aAhWLVywKHascC5oQ6AEIKDAA#v=onepage&q=pineal%20regularly%20present%20Xenarthra&f=false The Pineal Gland and its Endocrine Role] External links{{Wiktionary}}{{Wikispecies}}{{Commons category}}
4 : Xenarthrans|Chordate superorders|Extant Paleocene first appearances|Taxa named by Edward Drinker Cope |
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