Afrotheria

Cladus: Eukaryota
Supergroup: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Classis: Mammalia
Subclassis: Theria
Infraclassis: Placentalia
Superordo: Afrotheria
Cladus: Paenungulata
Ordines: Afrosoricida - Macroscelidea - Tubulidentata - †Embrithopoda - †Desmostylia

Name

Afrotheria

Vernacular names
日本語: アフリカ獣上目
‪Norsk (bokmål)‬: Afrotheria
Polski: afrotery
Português: Afrotérios
中文: 非洲獸總目

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Afrotheria is a clade of mammals, the living members of which include golden moles, sengis (also known as elephant shrews), tenrecs, aardvarks, hyraxes, elephants and sea cows.
Evolutionary relationships

Afrotheria was originally proposed in 1998[1] based on analyses of DNA sequence data. However, previous studies hinting at the close interrelationships among subsets of endemic African mammals date to the 1920s,[2] and much later sporadic papers in the 1980s[3] and 1990s.[4][5] The core of Afrotheria consists of the Paenungulata, i.e., elephants, sea cows, and hyraxes, a group with a long history among comparative anatomists.[6][7] Hence, while DNA sequence data have proven essential to infer the existence of Afrotheria as a whole, and while the insectivoran-grade afrotheres (tenrecs, golden moles, sengis) would probably not have been recognized as part of Afrotheria without DNA data, there is some precedent in the comparative anatomical literature for the idea that at least part of this group forms a clade.

Since the 1990s, increasing amounts of molecular and anatomical data have been applied that support the idea that afrotherian mammals are descended from a single common ancestor to the exclusion of other mammals. On the anatomical side, features shared by most or all afrotherians include a high vertebral count,[8] features of placentation,[9] shape of the ankle bones,[10][11] and relatively late eruption of the permanent dentition.[12] Studies of genomic data, including millions of aligned nucleotides sampled for a growing number of placental mammals, also support Afrotheria as a clade.[13][14]

Afrotheria is now recognized as one of four major groups within Eutheria (containing placental mammals).[15] Relations within the four cohorts, Afrotheria, Xenarthra, Laurasiatheria, and Euarchontoglires, and the identity of the placental root, remain somewhat controversial.[16] Afrotheria is a clade usually discussed without a Linnaean rank, but has been assigned the rank of cohort or magnorder, and superorder. One reconstruction that applies the molecular clock proposes that the oldest split occurred between Afrotheria and the other three some 105 million years ago when the African continent was separated from other major land masses.[17] This idea is consistent with the fossil record of Xenarthra, which is restricted to South America (following recent consensus that Eurotamandua is not a xenarthran[18]). However, Afrotheria itself does not have a fossil record restricted to Africa,[19] although this does seem to be true for the oldest, undisputed afrotherians.[20] Furthermore, the correspondence of Afrotherian origins with the Africa-South America tectonic split is not consistent with other applications of the molecular clock[21] or with the mammalian fossil record.[22] More recent, genomic-scale phylogenies favor the hypothesis that Afrotheria and Xenarthra comprise sister taxa at the base of the placental mammal radiation.[23]

Current status and distribution

Many members of Afrotheria appear to be at high risk of extinction. Species loss within this group would therefore comprise a particularly devastating loss of genetic and evolutionary diversity. The Afrotheria Specialist Group notes that Afrotheria as currently reconstructed includes nearly a third of all mammalian orders currently found in Africa and Madagascar, but only 75 out of more than 1200 mammalian species in those areas.

While most extant species assigned to the cohort Afrotheria live in Africa, some (such as the Indian elephant and three out of four species of sirenian) occur elsewhere; many of these are endangered as well. Prior to the Quaternary extinction event, proboscideans were present on every continent of the world except Australia and Antarctica. Hyraxes lived in much of Eurasia as recently as the end of the Pliocene; the extinct afrotherian orders of embrithopods and desmostylians were also once widely distributed.

Organization

Afrotheria is a clade of placental mammals, the stem designation for which is Eutheria. Note that ranks in Linnean taxonomy are arbitrary and without intrinsic biological meaning.[24] While this recognition does not mean that the Linnean system must be completely replaced,[25] it does have implications for high-level taxon names that, traditionally, are associated with certain suffixes (e.g., "oidea" need not be reserved for superfamily). Based on precedent, some clades listed below are junior synonyms and arguably should be replaced (e.g., Tenrecoidea McDowell 1958[26] instead of "Afrosoricida" Stanhope et al. 1998).

References

* Kriegs, Jan Ole, Gennady Churakov, Martin Kiefmann, Ursula Jordan, Juergen Brosius, Juergen Schmitz (2006). "Retroposed Elements as Archives for the Evolutionary History of Placental Mammals". PLoS Biol 4 (4): e91. doi:10.1371/journal.pbio.0040091. (pdf version)
* William J. Murphy, Eduardo Eizirik, Mark S. Springer et al. (14 December 2001). "Resolution of the Early Placental Mammal Radiation Using Bayesian Phylogenetics". Science 294 (5550): 2348–2351. doi:10.1126/science.1067179. PMID 11743200.
* Seiffert, Erik (2007). "A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological, and fossil evidence". BMC Evolutionary Biology 7: 13. doi:10.1186/1471-2148-7-224. (pdf version)


Notes

1. ^ Stanhope, M.J. et al. (1998) Molecular evidence for multiple origins of Insectivora and for a new order of endemic African insectivore mammals. Proc. Natl. Acad. Sci. U. S. A. 95, 9967–9972
2. ^ Le Gros Clark,W.E. & C.F. Sonntag. 1926. A monograph of Orycteropus afer III, the skull, the skeleton of the trunk, and limbs. Proceedings of the Zoological Society London 30: 445-485.
3. ^ DeJong,W.W., A: Zweers, and M. Goodman. 1981. Relationship of aardvark to elephants, hyraxes and sea cows from alpha-crystallin sequences. Nature 292: 538-540.
4. ^ DeJong,W.W., J.A.M. Leunissen, and G.J. Wistow. 1993. Eye lens crystallins and the phylogeny of placental orders: evidence for a Macroscelid–Paenungulate clade? pp. 5–12 in F. S. Szalay, M. J. Novacek, and M.C. McKenna (eds.), Mammal Phylogeny. Springer Verlag, New York.
5. ^ Springer, M.S. and Cleven, G.C. and Madsen, O. and De Jong,W.W. and Waddell, V.G. and Amrine, H.M. and Stanhope, M.J. 1997. Endemic African mammals shake the phylogenetic tree. Nature 388: 61--64.
6. ^ Simpson, G. G. 1945. The principles of classification and a classification of mammals. Bulletin of the American Museum of Natural History 85: 1-350.
7. ^ Tabuce R, Asher RJ, Lehmann T. 2008. Afrotherian mammals: a review of current data. Mammalia 72: 2-14.
8. ^ Sanchez-Villagra, M. R., Narita, Y. and Kuratani, S., Thoracolumbar vertebral number: the first skeletal synapomorphy for afrotherian mammals. Syst Biodivers 2007. 5: 1–17.
9. ^ Mess, A. and A.M. Carter. 2006. Evolutionary Transformations of Fetal Membrane Characters in Eutheria with Special Reference to Afrotheria. Journal of Experimental Zoology 306B:140–163.
10. ^ Tabuce, R., Marivaux, L., Adaci,M., Bensalah,M., Hartenberger, J. L., et al. Early tertiary mammals from north Africa reinforce the molecular afrotheria clade. Proc Royal Soc B-Biol Sci 2007. 274: 1159–1166.
11. ^ Seiffert, E., A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological, and fossil evidence. BMC Evol Biol 2007. 7: 13.
12. ^ Asher, R. J. and Lehmann, T. 2008. Dental eruption in afrotherian mammals. BMC Biol 6: 14.
13. ^ Murphy, W. J., Pringle, T. H., Crider, T. A., Springer, M. S. and Miller, W., Using genomic data to unravel the root of the placental mammal phylogeny. Genome Res 2007. 17: 413–421.
14. ^ Nikolaev, S., Montoya-Burgos, J. I., Margulies, E. H., Program, N. C. S., Rougemont, J., et al. Early history of mammals is elucidated with the ENCODE multiple species sequencing data. PLoS Genet 2007.3: e2.
15. ^ Murphy, W. J., Eizirik, E., O’Brien, S. J., Madsen, O., Scally, M., et al. Resolution of the early placental mammal radiation using Bayesian phylogenetics. Science 2001. 294: 2348–2351.
16. ^ Asher RJ, Bennett N, Lehmann T. 2009. The new framework for understanding placental mammal evolution. Bioessays 31(8): 853-864.
17. ^ Springer MS, Murphy WJ, Eizirik E, O'Brien SJ: Placental mammal diversification and the Cretaceous-Tertiary boundary. Proc Natl Acad Sci USA 2003, 100(3):1056-1061.8.
18. ^ Rose KD, Emry RJ, Gaudin TJ, Storch G. 2005. Chapter 8, Xenarthra and Pholidota. in: Rose KD and Archibald JD (eds.), The Rise of Placental Mammals: Origins and Relationships of the Major Extant Clades. Johns Hopkins University Press, Baltimore, MD.
19. ^ Zack, S.P., T.A. Penkrot, J.I. Bloch and K.D. Rose. 2005. Affinities of ‘‘hyopsodontids’’ to elephant shrews and a Holarctic origin of Afrotheria. Nature 434: 497–501.
20. ^ Robinson, T.J. and E.R. Seiffert. 2004. Afrotherian origins and interrelationships: new views and future prospects. Curr. Top. Dev. Biol. 63: 37–60.
21. ^ Kitazoe Y et al. 2007. PloS ONE 2,e384
22. ^ Archibald JD, Deutschmann DH. 2001. J. Mamm. Evol. 8:107-124.
23. ^ Prasad, A. B. Allard, M. W., NISC Comparative Sequencing Program and Green, E. D., Confirming the phylogeny of mammals by use of large comparative sequence data sets. Mol Biol Evol 2008. 25: 1795–1808
24. ^ Kuntner M, Agnarsson I. 2006. Are the Linnean and Phylogenetic Nomenclatural Systems Combinable? Recommendations for Biological Nomenclature. Systematic Biology 55:774-784
25. ^ Forey PL. 2002. PhyloCode: Pain, No Gain. Taxon 51:43-54.
26. ^ McDowell, S. B. 1958. The Greater Antillean insectivores. Bulletin of the American Museum of Natural History 115: 115--213.
27. ^ Seiffert (2007) provides an overview of possible resolutions to the polytomy of Afrosoricida, Macroscelidea, Tubulidentata, and Paenungulata. There is currently no broadly supported consensus on this aspect of afrotherian phylogeny.

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