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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. They are also characterized by having a shorter fibula relative to the tibia. Epitheria — like Xenarthra and Afrotheria — originated after the K-Pg boundary , with the placental diversification occurring within the first hundred thousand years after the K-Pg event and the first modern placental orders began appearing 2–3 million years later. Epitheres are one of the most successful groups of animals. The monophyly of Epitheria has been challenged by molecular phylogenetic studies.〔For example: Springer, Mark S., Michael J. Stanhope, Ole Madsen, and Wilfried W. de Jong. 2004. (Molecules consolidate the placental mammal tree )" ''Trends in Ecology and Evolution'' 19:430–438.〕 While preliminary analysis of a set of retroposons shared by both Afrotheria, and Boreoeutheria (presence/absence data) supported the Epitheria clade,〔Kriegs, Jan Ole, Gennady Churakov, Martin Kiefmann, Ursula Jordan, Juergen Brosius, and Juergen Schmitz. (2006) (Retroposed Elements as archives for the evolutionary history of placental mammals )" ''PLoS Biol'' 4(4) e91.〕 more extensive analysis of such transposable element insertions around the time of the divergence of Xenarthra, Afrotheria, and Boreoeutheria strongly support the hypothesis of a near-concomitant origin (trifurcation) of these three superorders of mammals.〔Nishihara, H., Maruyama, S. & Okada, N. 2009. Retroposon analysis and recent geological data suggest near-simultaneous divergence of these three superorders of mammals. ''PNAS'' 106: 5235-40.〕〔Churakov, G., Kriegs, J.O., Baertsch, R., Zemann, A., Brosius, J. & Schmitz, J. 2009. Mosaic retroposon insertion patterns in placental mammals. ''Genome Research'' 19: 868-75.〕 Another analysis suggests that the root of this clade lies between the Atlantogenata and Boreoeutheria.〔Song S, Liu L, Edwards SV, Wu S (2012) Resolving conflict in eutherian mammal phylogeny using phylogenomics and the multispecies coalescent model. Proc Natl Acad Sci USA〕 }} }} == Alternative hypotheses == Alternative hypotheses place either Atlantogenata and Boreoeutheria, or Afrotheria and Exafroplacentalia (Notolegia) at the base of the tree: }} }} }} One Bayesian analysis places the root between Atlantogenata and Boreoeutheria.〔Morgan CC, Foster PG, Webb AE, Pisani D, McInerney JO, O'Connell MJ (2013) Heterogeneous models place the root of the placental mammal phylogeny" ''Mol Biol Evol'' 30(9) 2145-256 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Epitheria」の詳細全文を読む スポンサード リンク
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