Simplified tree showing relationships between 18 extant orders of placental mammals, inferred from a consensus phylogeny integrating molecular evidence . Separate suborders are shown for Rodentia (n = 3) and Primates (n = 2). Four superorders have been recognized (top bar; X = Xenarthra). Note the relatively rapid diversification of placental orders between 80 and 100 million years ago (Ma).
Martin Journal of Biology 2008 7:13 doi:10.1186/jbiol74