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.
Epitheres are though to have appeared in the early part of the Late Cretaceous age.[citation needed] Before the end of the Mesozoic Era, ancestral forms of most of the living orders (such as the ungulates and the insectivores) had already appeared. After the extinction of non-avian dinosaurs (in the Early Paleocene), the epitheres' diversity exploded, and by the end of the Eocene, all living orders of Epitheria had appeared. Epitheres are one of the most successful groups of animals.
Monophyly of Epitheria has been challenged by molecular phylogenetic studies[1]. While preliminary analysis of a set of retroposons shared by both Afrotheria, and Boreoeutheria (presence/absence data) supported the Epitheria clade[2], 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[3][4].
[edit] Alternative hypotheses
Alternative hypotheses place either Atlantogenata and Boreoeutheria, or Afrotheria and Exafroplacentalia (Notolegia) at the base of the tree:
[edit] References
- ^ 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.
[edit] External links
- 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
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