The first Reginald Rivers short story "A Gun for Dinosaur" was published in 1956, in response, de Camp says, to gross scientific inaccuracies he had seen in fiction about adventures among dinosaurs. He wanted to write a story that was scientifically plausible, in which the era into which his characters ventured was rendered as accurately as scientific knowledge would permit. "A Gun for Dinosaur" became one of the most popular of science fiction short stories, anthologized often. When asked by Robert Silverberg to contribute a dinosaur story to an anthology Silverberg was editing, de Camp revived Reginald Rivers and in the 1990s wrote several new stories of his adventures. These stories have in common adventures in carefully depicted ancient eras in North America, wayward clients who seem more trouble than they are worth, and Rivers's engaging sense of humor. Evolution as a topic does not dominate most...