Epitheria

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
Temporal range: Late Cretaceous - Recent
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Clade: Eutheria
Infraclass: Placentalia
Clade: Epitheria
Orders and Clades

Epitheria — like Xenarthra and Afrotheria — originated after the K-Pg boundary 66 million years ago, 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.[1] Epitheres are one of the most successful groups of animals.

The monophyly of Epitheria has been challenged by molecular phylogenetic studies.[2] While preliminary analysis of a set of retroposons shared by both Afrotheria, and Boreoeutheria (presence/absence data) supported the Epitheria clade,[3] 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.[4][5]

Another analysis suggests that the root of this clade lies between the Atlantogenata and Boreoeutheria.[6]

Placentalia  
 

Xenarthrans

 
  Epitherians  
 

Afrotherians

 
  Boreoeutherians  
 

Euarchontoglires

 
 

Laurasiatherians

 
 
 
 

Alternative hypotheses

Alternative hypotheses place either Atlantogenata and Boreoeutheria, or Afrotheria and Exafroplacentalia (Notolegia) at the base of the tree:

Placentalia  
  Atlantogenata  
 

Xenarthra

 
 

Afrotheria

 
 
  Boreoeutheria  
 

Euarchontoglires

 
 

Laurasiatheria

 
 
 
Placentalia  
 

Afrotheria

 
  Exafroplacentalia  
 

Xenarthra

 
  Boreoeutheria  
 

Euarchontoglires

 
 

Laurasiatheria

 
 
 
 

One Bayesian analysis places the root between Atlantogenata and Boreoeutheria.[7]

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References
  1. O'Leary, M. A.; Bloch, J. I.; Flynn, J. J.; Gaudin, T. J.; Giallombardo, A.; Giannini, N. P.; Goldberg, S. L.; Kraatz, B. P.; Luo, Z.-X.; Meng, J.; Ni, X.; Novacek, M. J.; Perini, F. A.; Randall, Z. S.; Rougier, G. W.; Sargis, E. J.; Silcox, M. T.; Simmons, N. B.; Spaulding, M.; Velazco, P. M.; Weksler, M.; Wible, J. R.; Cirranello, A. L. (2013). "The Placental Mammal Ancestor and the Post-K-Pg Radiation of Placentals". Science. 339 (6120): 662–667. doi:10.1126/science.1229237. ISSN 0036-8075. PMID 23393258. S2CID 206544776.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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
  7. 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. PMC 3748356. PMID 23813979.
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