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 millions years later. 66 million years ago Epitheres are one of the most successful groups of animals. 1
Monophyly of Epitheria has been challenged by molecular phylogenetic studies. While preliminary analysis of a set of 2 retroposons shared by both Afrotheria, and Boreoeutheria ( presence/absence data) supported the Epitheria clade, more extensive analysis of such 3 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. 4 5
Another analysis suggests that the root of this clade lies between the Atlantogenata and Boreoeutheria.
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.
^ O'Leary, MA; Bloch, JI; Flynn, JJ; Gaudin, TJ; Giallombardo, A; Giannini, NP; Goldberg, SL; Kraatz, BP; Luo, ZX; Meng, J; Ni, X: Novacek, MJ; Perini, FA; Randall, ZS; Rougier, GW; Sargis, EJ; Silcox, MT; Simmons, NB; Spaulding, M; Velazco, PM; Weksler, M; Wible, JR; Cirranello, AL (8 February 2013). "The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals". Science 339 (6120): 662–7. doi: 10.1126/science.1229237. OCLC 827160921. PMID 23393258 . Retrieved February 2013.
^ 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.
^ 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.
^ 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.
^ 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
^ 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 doi: 10.1093/molbev/mst117
Summary of molecular support for Epitheria
Waddell PJ, Kishino H, Ota R. 2001. A phylogenetic foundation for comparative mammalian genomics. Genome Inform Ser Workshop Genome Inform 12: 141–154
Mark S. Springer, William J. Murphy, Eduardo Eizirik, and Stephen J. O'Brien (Edited by Morris Goodman). 2002 Placental mammal diversification and the Cretaceous-Tertiary boundary
Wildman D.E.; Chen C.; Erez O.; Grossman L.I.; Goodman M.; Romero R. 2006. Evolution of the mammalian placenta revealed by phylogenetic analysis" PNAS 103 (9) 3203–3208
Nikolaev, S., Montoya-Burgos, J.I., Margulies, E.H., Rougemont, J., Nyffeler, B., Antonarakis, S.E. 2007. Early history of mammals is elucidated with the ENCODE multiple species sequencing data" PLoS Genet 3:e2, doi: 10.1371/journal.pgen.0030002.
Gennady Churakov, Jan Ole Kriegs, Robert Baertsch, Anja Zemann, Jürgen Brosius, Jürgen Schmitz. 2008. Mosaic retroposon insertion patterns in placental mammals