Figure 1.

Phylogenetic splitting topology and approximate ages for mammalian divergences discussed in this article. Shaded boxes indicate approximate ranges for divergence date estimates extracted from multiple literature sources cited in the main text and footnote 2. Approximate dates for the earliest (deepest) divergences among extant species within the eutherian and metatherian lineages are indicated by arrowheads. As for the branching points, the shaded boxes associated with arrowheads indicate approximate range estimates for these basal divergence dates.