L. Sprague de Camp," felt "[t]he book reads ... like a pleasant and informal lecture, given at their ease, by a pair of enormously rational and urbane individuals" with which he found it "virtually impossible to find fault." He singled out the way the de Camps "make the dinosaurs come alive by picturing them in action" and the "most remarkable first chapter ... which ... is an evocation (the best I know) of a typical day in the Mesozoic." He felt that "[t]he book deals, satisfactorily, with the paleontologists and their discoveries, too, especially with the Cope-Marsh feud [and] with the effects on contemporary man of the great discoveries of paleontology; the impetus given to the search for giant living creatures--and to romancing about them--and the ferocious object lesson given on the subject of mass extinctions." He also notes that the de Camps point out "[w]e are in the midst of [another] great dying now, ... brought on by man himself." The Booklist characterized the book as "[a]n informative, comprehensible, often lively survey of the Age of Reptiles and the careers of some of the scientists who found and studied dinosaur fossils." Science Books rated it "[a] very comprehensive book about Mesozoic reptiles, [with] [t]the text ... quite free of inaccuracies and... accompanied by many good illustrations," and "[t]he writing style [as] fluctuat[ing] between ... humorous whimsy and scientific exposition, which may limit its popularity." It called "[t]he section [on] the history of the early fossil hunters and development of the great natural history museums ... a real contribution, since this information is collected from many disparate sources." Philip and Phylis Morrison, writing for Scientific American, found it "excellent and fresh, ... lively and intelligent," "a savory mixture of biology and history, ... cover[ing] a wide range of lore and logic, from genetics and the problem of extinction to the scaling of beasts." "Skeptical and yet imaginative," they wrote, "the text lives up to the De Camp reputation." They found the book's "final imaginary safari in the Jurassic ... logically planned: for the big flesh-eaters one had best carry a real elephant gun, the Continental .600 or perhaps the Holland & Holland double express .500." Bruce Fleury, in a retrospective more than twenty years after the book's initial publication, noted that it "precede[d] the 'dinosaur renaissance' but remain[ed a] valuable and readable introduction to the subject" and "[l]ike De Camp's