Dunkleosteus hunting primitive sharks. Computer artwork of a Dunkleosteus terrelli prehistoric predatory marine fish about to catch a six-foot-long Cladoselache sp. primitive shark in the Rheic Ocean, around 370 million years ago in what is now North America. This hypercarnivore measured nearly as long as a school bus and lived during the Late Devonian period (around 380-360 million years ago). It is one of the largest arthrodire placoderms (armoured fish) to have ever lived.