The massive swimming reptiles called mosasaurs thrash their powerful tails to propel them after prey. Four articulated, webbed paddles let them precisely steer their paths, and their hinged jaws-much like a snake's-allow mosasaurs to swallow larger creatures than their size would indicate. A small set of secondary pterygoid jaws in their gullets pull in their meals for more efficient digestion. As air breathers, mosasaurs must stay near the surface of the water, competing for food with whales. This proximity to the surface means they often capsize small boats, feasting on the crew members who fall out.