"Time's Arrow" is a short story by Arthur C. Clarke, first published in 1950.
This is the story of a human visit to time when dinosaurs still roamed earth, in a time machine.
Dr. Henderson's discovery of negative entropy allows a paleontologist and himself to travel back fifty million years - straight into the jaws of a massive predator. Their untimely end is discovered by the paleontologist's two assistants in the present day who discover the tracks of both the monster and the battered research Jeep.
Probably accidentally, as hinted towards the end of the story.
