On a muddy riverbank, a hungry dinosaur stalks her prey. From her hiding place in the nearby trees, she spies a giant, four-legged plant eater. At the right moment, she leaps from the trees and lunges at the slower dinosaur, tearing at its flanks with teeth and sharp claws. It's an average day in southern Texas, 115 million years ago. This dinosaur attack happened. We know for certain, because these two animals left their footprints in the mud --...