Molecular dating of basal placental divergences and the Cretaceous/Tertiary boundary. Chronogram with branch lengths proportional to time units obtained from the partitioned analysis of the complete ADRA2B + BRCA1 + VWF (codon positions 1+2+3) placental nucleotide dataset (5130 sites). The geological timescale for the Cretaceous and Tertiary eras is superimposed (Paleo. = Paleocene; Oligo. = Oligocene; P. = Pliocene). The thick horizontal dashed line marks the Cretaceous/Tertiary boundary (K/T) at 65 Mya. The grey shaded area representing the Late Cretaceous era illustrates the fact that the major placental divergences occurred within this time window. The names of basal placental clades (yellow diamonds) and calibration nodes (red stars) referring to Table 1 are indicated (PAE: PAEnungulata, MUR: MURidae, MEG: MEGachiroptera, PER: PERissodactyla, ART: CetARTiodactyla, and CET: CETacea). The xenarthran subtree is highlighted in bold and numbering of nodes refers to Table 1.