Xiphactinus is a fish that lived about seventy million years ago, in a vast, shallow sea that stretched across what today is the center of the North American continent. It was one of the most ferocious inhabitants of that ancient sea.

The most impressive part of a Xiphactinus is its rather bulldog-like expression, with its upturned jaw and giant, fang-like teeth. The jaw was very mobile, capable of opening wide to take in large-sized prey.

Xiphactinus' pectoral fins were held out by solid bony fin rays, giving the appearance of wings. Its body was long -- fifteen to twenty feet -- and there were more than 100 vertebrae along its backbone. Its tail was deep and forked, attached to the body at a narrow base. All of these attributes indicate that Xiphactinus was an extremely fast, powerful swimmer and an active, efficient predator. Other Xiphactinus fossils have been found with very large fish inside the body cavity, swallowed whole.