Size and Weight:
Xiphactinus was the largest bony fish of the Cretaceous period, but it was far from the top predator of its North American ecosystem--as we can tell from the fact that specimens of the prehistoric sharks Squalicorax and Cretoxyrhina have been found containing Xiphactinus remains. It's a fish-eat-fish world, though, so you shouldn't be surprised to learn that numerous Xiphactinus fossils have been found containing the remains of smaller fish. (Finding a fish inside a fish inside a shark would be a true fossil trifecta!)
One of the most famous Xiphactinus fossils contains the almost-intact remains of an obscure, 10-foot-long Cretaceous fish called Gillicus. Paleontologists speculate that the Xiphactinus died right after swallowing the fish, possibly because its still-living prey managed to puncture its stomach. If this is what happened, Xiphactinus would be the first fish proven to have died from acute indigestion.