O’Brien celebrates 14 prehistoric monsters by presenting each with a modern object or a human, thereby giving readers information about the size of these giants. Dinosaurs, in full-color and full-snarl, dominate the double-page layouts as they frolic and menace an airplane, fire truck, tank, automobile, and assorted people. For every creature, O’Brien provides the name, its meaning, and a brief line of text. Three of the creatures presented are not dinosaurs at all—Quetzalcoatlus, a pterosaur, Phobosuchus, a relative of the crocodiles, and Dinichthys, a bony fish—which the author mentions in the back matter. The illustrations are not drawn to scale, e.g., if Spinosaurus is really 49 feet long, as the text indicates, the car it is shown next to would appear to be 30 feet long. Readers may have to puzzle over a few scenes, but will enjoy browsing through this book, from the dramatic eyeball view of a toothy Tyrannosaurus rex on the cover to the final head-on glare from a Triceratops. (Picture book/nonfiction. 5-9)