Turning from mystery monsters to real ones, Cohen gets off to a halting start, seemingly uncertain as to whether he is confirming or dispelling the ""myths"" that all dinosaurs were huge, slow, and stupid. But once into the question of their extinction, he does a reasonable job of reviewing the various theories that have been brought forth: that the dinosaurs couldn't adapt to a cooler climate, geological shifts, or changes in plant life; that they couldn't compete with emerging mammals; that they were wiped out by some epidemic, by radiation from a supernova, or by a self-protective toxic chemical developed by the new Cretaceous foliage. (All of these suggestions, incidentally, are reviewed in Desmond's adult book The Hot-Blooded Dinosaurs, 1976.) Cohen summarizes the major objections to all the proposals, and concludes that it was probably a combination of factors that killed the dinosaurs and other Cretaceous life forms. He points out that other ""Great Deaths"" occurred at the ends of the Permian and the Pleistocene periods: and ends with the reminder that one branch of the dinosaurs seems to have survived as birds. A fair synopsis overall--and Wells' full-page, black-and-white illustrations are restrained and attractive, as dinosaur pictures go.