Taken from the cover flap of the novel DANGER: DINOSAURS! by Richard Marsten aka Evan Hunter, Ed McBain:
Owen Spencer would never have agreed to lead the time-slip expedition back to the Jurassic period - the Age of Reptiles - had he foreseen the terrifying experiences in store for the small group making the expedition. Chartering the expedition was Dirk Masterson, a treacherous big-game hunter, whose alleged purpose was to take pictures of the enormous reptiles that roamed Jurassic times. Even when Masterson smashed the jeep into the force field, destroying the only protection that stood between the group and the lumbering beasts, Owen could not be sure it was an accident.
Richard Marsten has written a fast-moving tale of people stranded on earth in its infancy and forced to pit their ingenuity and strength against mammoth reptiles. It might not have been so bad if Masterson, with his mania for big-game hunting, had not continued to shoot at every reptile he spotted. But his madman tactics repeatedly aroused the fury of the hideous dinosaurs, whose attacks drove them farther and farther away from the relay area that would slip them back to the present when the week was up.
The weird circumstances that made Owen's brother, Chuck, take over the leadership of the expedition and the even stranger adjustment of the time stream that left the party with the inexplicable feeling that somebody was missing makes Danger: Dinosaurs! an unusual and fascinating treatment of the ever-provacative time theme. The desperate search for the relay area, interrupted by fierce fights with the flesh-eating monsters, and an earthquake that creates a chaos of stampeding animals give this story action that is as alien as any distant planet.