The third major type of response of organisms to global climatic change is extinction: failure to survive the new conditions. The Quaternary is characterized by its particularly extreme climatic oscillations, and also for the occurrence of wholescale extinctions of large mammals at about the glacial–Holocene transition (Grayson 1984a). Extinction has certainly occurred, but how widespread is it as a response to global climatic change? In the search for ‘causes’ or ‘explanations’ of the late-Quaternary mammalian extinctions, it is necessary to look away from mammals at this time and towards other groups at other times during the Quaternary. Is the transition at the beginning of the Holocene a particularly unusual transition compared to other parts of the Quaternary? There have been other oscillations of climate during the Quaternary as extreme as the transition at the beginning of the Holocene (for example Shackleton & Opdyke 1973; Martinson et al. 1987; see also Fig. 4.3). And why mammals, and not other groups?

Animals

Webb (1984) showed that there have been several periods during the last 10 Myr when rates of extinction among North American mammals have been high. The most severe episode, at about 5 Ma, involved 62 genera, of which 35 were large mammals (>5 kg body weight). The episode at the glacial–Holocene transition, by contrast, involved 43 genera, of which 39 were large mammals. There are three other episodes within the last 10 Myr with extinctions of a similar magnitude (Fig. 7.1).