"It's an astonishingly diverse marine ecosystem—huge numbers of fish, sharks, sea turtles, long-necked plesiosaurs and of course the mosasaurs," Longrich said. "We are seeing extraordinarily ...

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.

Predators likely included some of the fiercest monsters of the seas, such as the sharp-toothed shark Cretoxyrhina and the giant mosasaur Tylosaurus. Like all plesiosaurs, Styxosaurus's limbs were ...