Dunkleosteus dates from the Late Devonian (365 million years ago) of Ohio. This animal was the “big fish” of the Devonian seas, being the top predator of its ancient ecosystem. The fearsome jaws are perhaps evidence enough, but we know from bite marks on bones and other evidence that Dunkleosteus ate its own kind, as well as sharks and smaller fish.

During the Devonian Period, Ohio and the surrounding area was covered by an ocean inhabited by many now-extinct fish and sharks. Stagnant bottom waters sometimes preserved the remains of dead animals as they sank to the sea floor. These fossils are often found within nodules now exposed in stream beds and cliffs. One of these nodules can be seen in the photograph at the bottom right.