The title does this an injustice, makes it sound like another foray into prehistoric life; rather it is an introduction to the successive cycles of thermal change that determined the nature and distribution of animal and human population, concluding with an alert: ""Great snowstorms may come again some day to North America. A new ice age may begin."" All this is presented in words of few syllables, in the simplest possible concepts, in a very attractive, effective picture book format.