Laurasiatheria is a large group of placental mammals believed to have originated on the northern supercontinent of Laurasia. It includes shrews, hedgehogs, pangolins, bats, whales, most hoofed mammals, and carnivorans, among others.
[edit] Classification and phylogeny
Laurasiatheria was discovered on the basis of the similar gene sequences shared by the mammals belonging to it. No anatomical features have yet been found that unite the group. Laurasiatheria is a clade usually discussed without a Linnaean rank, but has been assigned the rank of cohort or magnorder, and superorder. The Laurasiatheria clade is based on DNA sequence analyses and retrotransposon presence/absence data. The name comes from the theory that these mammals evolved on the supercontinent of Laurasia, after it split from Gondwana when Pangaea broke up. It is a sister group to Euarchontoglires (or Supraprimates) with which it forms the clade Boreoeutheria. Laurasiatheria includes the following extant taxa:
- Eulipotyphla, having subsumed:
- Chiroptera: bats (cosmopolitan)
- Perissodactyla: odd-toed ungulates including horses, tapirs and rhinoceroses
- Cetartiodactyla[2] (unranked) containing the orders:
- Cetacea: whales, dolphins and porpoises
- Artiodactyla: even-toed ungulates including camels, pigs, ruminants (giraffes, deer, antelopes, cattle, sheep, goats, etc.) and hippopotamuses; now recognized to be paraphyletic.
- Ferae (unranked) containing the orders:
- Pholidota: pangolins, aka 'scaly anteaters' (Africa, South Asia)
- Carnivora: cats, dogs, bears, seals, and others (cosmopolitan)
There is still uncertainty regarding the phylogenetic tree for extant Laurasiatherians, primarily due to disagreement about the placement of Chiroptera and Perissodactyla. Based on morphological grounds, Chiroptera had long been classified in the superorder Archonta (e.g. along with treeshrews and the gliding colugos) until genetic research ruled that out and instead showed their kinship with the other Laurasiatherians.[3] The studies conflicted in terms of the exact placement of Chiroptera however, with it being linked most closely to groups such as Eulipotyphla,[4] Ferae[5] or with Perissodactyla and Ferae in the Pegasoferae proposal.[6] The most recent study (Zhou et al., 2011[7]) found that "trees reconstructed [...] for the 1,608-gene data set fully support [...] a basal position for Eulipotyphla and a more apical position for Chiroptera" (see cladogram below) and concluded that "Pegasoferae [...] does not appear to be a natural group." The exact position of Perissodactyla remains less certain however, with some studies linking it with Ferae into a proposed clade Zooamata while others unite it with Cetartiodactyla into Euungulata, a clade of 'true ungulates'; Zhou et al. find better (but not full) support for the latter.
Laurasiatheria is also posited to include several extinct orders and superorders:
[edit] References
- ^ Waddell, Peter J., Okada, Norihiro, & Hasegawa, Masami (1999). "Towards resolving the interordinal relationships of placental mammals". Systematic Biology 48 (1): 1–5. doi:10.1093/sysbio/48.1.1. PMID 12078634.
- ^ Nikaido, M., Rooney, A. P. & Okada, N. (1999). "Phylogenetic relationships among cetartiodactyls based on insertions of short and long interpersed elements: Hippopotamuses are the closest extant relatives of whales". Proceedings of the National Academy of Sciences 96 (18): 10261–10266. doi:10.1073/pnas.96.18.10261. PMC 17876. PMID 10468596. http://www.pnas.org/content/96/18/10261.full. Retrieved 03 October 2011.
- ^ Pumo et al (1998)
- ^ Cao et al (2000)
- ^ Matthee et al (2007)
- ^ Nishihara et al (2006)
- ^ Zhou, X. et al. (2011). "Phylogenomic analysis resolves the interordinal relationships and rapid diversification of the Laurasiatherian mammals". Systematic Biology. doi:10.1093/sysbio/syr089. http://sysbio.oxfordjournals.org/content/61/1/150. Retrieved 07 January 2012. (published online 07 September 2011)
[edit] Further reading
- William J. Murphy, Eduardo Eizirik, Mark S. Springer et al., Resolution of the Early Placental Mammal Radiation Using Bayesian Phylogenetics,Science, Vol 294, Issue 5550, 2348–2351, 14 December 2001.
- Jan Ole Kriegs, Gennady Churakov, Martin Kiefmann, Ursula Jordan, Jürgen Brosius, Jürgen Schmitz. (2006) Retroposed Elements as Archives for the Evolutionary History of Placental Mammals. PLoS Biol 4(4): e91.[1] (pdf version)
- Kitazoe Y, Kishino H, Waddell PJ, Nakajima N, Okabayashi T, et al. (2007) "Robust Time Estimation Reconciles Views of the Antiquity of Placental Mammals." PLoS ONE 2(4): e384. doi:10.1371/journal.pone.0000384
[edit] External links
- Waddell PJ, Kishino H, Ota R. 2001. A phylogenetic foundation for comparative mammalian genomics. Genome Inform Ser Workshop Genome Inform 12: 141–154
- 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
- Goloboff, P.A.; Catalano, S.A.; Mirande, J.M.; Szumik, C.A.; Arias, J.S.; Källersjö, M & Farris, J.S. 2009. Phylogenetic analysis of 73 060 taxa corroborates major eukaryotic groups. Cladistics 25 (3): 211–230
