The Fountain of Youth was located in a cavern near the town. Some dinosaur fossils had been brought back to life by the water of the fountain. The Sheriff and several of his men were killed by dinosaurs.
More dinosaurs, velociraptors, were brought back to life when the Master found the fountain. He and the dinosaurs were defeated by inhabitants of Eternity, along with the Fifth Doctor and Peri. (PROSE: A Town Called Eternity)