Thursday, October 18, 2007

The Family Tree of the Placental Mammals

In PNAS Genomics, biogeography, and the diversification of placental mammals
Among the placental mammals, phylogenetic branching events have been inferred by using either nucleotide sequence data (4–11) or rare insertion/deletion patterns (12–15). Many of the results recognize four primary eutherian groups: Afrotheria, Xenarthra, Laurasiatheria, and Euarchontoglires. Afrotherians (e.g., elephants, hyraxes, manatees, aardvarks, tenrecs, and allies) are a clade of mammals that originated in Africa, and whose extant members still mostly remain on that continent with the exception of Asian elephants and sirenians such as the Florida manatee. The Xenarthra includes the sloths, armadillos, and anteaters that today are restricted to South and Central America (although some Xenarthra, such as the nine-banded armadillo, have recently dispersed to North America). The Laurasiatheria (e.g., bats, eulipotyphlans, pangolins, carnivores, perrisodactyls, and cetartiodactyls) is a diverse clade including extant lineages that originated in the ancient northern continent of Laurasia. The Euarchontoglires includes the species from five living mammalian orders (e.g., primates, treeshrews, flying lemurs, rabbits, and rodents). This last group remains the most controversial, and a number of recent studies have suggested it is not valid (4, 6, 7).

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