Dinosaur Lake V: Survivors - Dinosaur Lake, #5

The predatory dinosaurs, amphibious, land-crawlers, air flyers, small and large, were dead; dead in all the forests, mountains, deserts, towns, and cities of America, and across the planet. They were still hunted, sought and exterminated when found, and these rogue beasts were becoming rarer every day. The humans' dinosaur killing serum, and extermination practices, had worked far better than anyone had prayed for, and they had eventually freed the planet of its primordial scourge.
The earth belonged to the humans once more  and all its lands were safe-or so the world, Henry Shore, former Chief Park Ranger at Crater Lake National Park, and his wife, Ann, had believed.until one day years later two new dinosaurs, craftier than any the earth had ever seen, appeared. One of them was benevolent, a friend to mankind, and the other was not. It was blood-thirsty, eerily intelligent  and unbelievably vengeful.
This dinosaur wouldn't be so easy to kill. *** There are now six Dinosaur Lake books.