Higher level relationships among placental mammals, as well as the historic
al biogeography and morphological diversification of this group, remain unc
lear(1-3). Here we analyse independent molecular data sets, having aligned
lengths of DNA of 5,708 and 2,947 base pairs, respectively, for all orders
of placental mammals. Phylogenetic analyses resolve placental orders into f
our groups: Xenarthra, Afrotheria, Laurasiatheria, and Euarchonta plus Glir
es. The first three groups are consistently monophyletic with different met
hods of analysis. Euarchonta plus Glires is monophyletic or paraphyletic de
pending on the phylogenetic method. A unique nine-base-pair deletion in exo
n 11 of the BRCA1 gene provides additional support for the monophyly of Afr
otheria, which includes proboscideans, sirenians, hyracoids, tubulidentates
, macroscelideans, chrysochlorids and tenrecids. Laurasiatheria contains ce
tartiodactyls, perissodactyls, carnivores, pangolins, bats and eulipotyphla
n insectivores. Parallel adaptive radiations have occurred within Laurasiat
heria and Afrotheria. In each group, there are aquatic, ungulate and insect
ivore-like forms.