Figure 2.

ML tree topology (−lnL = 19019.05697) combined with calculated dates of divergences as well as estimates of generic diversity of relevant fossil taxa (gray-shaded boxes). Generic diversity estimates are from ref. 32. Only genera considered stable enough and based on diagnostic material are considered. Numbers of extant species are given between parentheses for each group. Vertical colored boxes indicate habitat: green, specialization in filter feeding (baleen whales); dark blue, specialization for deep feeding on squids (beaked and sperm whales); orange, coastal waters; light blue, oceanic waters; and red, fluvial environment (whereas the boto, baiji, and susu are exclusively riverine, some delphinoid species consist of distinct coastal and fluvial populations). Each horizontal yellow bar indicates twice the value of the standard deviation for the age of the corresponding node. Hence, standard deviations are not referring to the topology of the tree. Dotted triangles indicate the radiation of Delphinidae and concurrent gradual extinction of Waipitiidae, Squalodelphidae, and Squalodontidae. The black arrow at the base of the tree indicates the position of the root when all nu and mt data are used in a simultaneous ML analysis and by using hippopotamus as an outgroup. This result is, however, unstable because several gene fragments support an alternative root, indicated by the white arrow. Whichever of these two rooting hypotheses is correct is irrelevant to the issues discussed and conclusions reached in the present paper. P, Pliocene and p, Pleistocene.