In the heart of the Late Jurassic, a shadow slips through the forest. The hunter is restless. Allosaurus fragilis—the most common predator of its age—prowls the floodplain. Its head sways from side to side, nostrils testing the wind, as it tracks the scent of a herd of herbivores. With long, muscular legs and jaws lined with serrated teeth, this predator is the ruling hunter of the North American world.