Frequency histograms showing distribution of node ages within mustelids and four other vertebrate taxa. Mean node ages for mustelids are based on 28.5 MYA root age and 24 MYA crown age priors (see Table 2). The top panel shows ocean temperature curve (smoothed mean in red) based on global deep-sea oxygen isotope (δO18) records (modified from ). The development of full-scale ice-sheets in each hemisphere as well as key changes in vegetation in the northern hemisphere during the Neogene are also shown. Following the Mid-Miocene climatic optimum, forested habitats (A) gave way to more open vegetation habitats such as woodlands and grasslands (B). Taiga forests greatly expand during the Pliocene (C). See the text for further details. PLE. denotes Pleistocene.