Mosasaur - 65 Million Years Ago A giant, meat-eating marine reptile (not a dinosaur) that lived during the late Cretaceous period. It was up to 10 m long. Mosasaurs had four paddle-like limbs on a long, streamlined body and a long, powerful tail. The large head had huge jaws (up to 1.45 m long) with many teeth. The jaws could open about 3 feet (1 m). The lower jaw is loosely hinged to the skull with a moveable joint on each side (behind the teeth). This loose joint let it swallow huge prey, like some snakes. They hunted fish, turtles, mollusks, and shellfish.