A 13-foot-long (4-meter-long) Xiphactinus could open its jaw wide enough to swallow six-foot-long (two-meter-long) fish whole, but it itself was occasionally prey to the shark Cretoxyrhina.

Evidence suggests Cretoxyrhina fed on mosasaurs, plesiosaurs, and even the giant bony fish Xiphactinus, a fierce predator itself. Sharks are made of cartilage, which does not fossilize well.