[3] As stated on the dust cover of the Doubleday edition, the work is a survey of "the exciting story of the lost world of the great reptiles and of the fossil hunters who discovered them millions of years later.

Publishers' Weekly called the book "clear, comprehensive, [and] well-researched," noting that it "begins as a vivid and scientifically sound depiction of the age of the giant dinosaurs [and] develops into an impressive tribute to the science of paleontology.

"[6] In Natural History Isaac Asimov, noting that "few people ... can speak more charmingly and enlightenedly about scientific subjects than 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."

"[9] 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."

"[10] 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 many other popular works on scientific topics, ... well written and ... highly recommended.