Dunkleosteus: Powerful Armored Devonian Fish

Dunkleosteus was a genus of armored fish called placoderms that lived during the Devonian Period, from about 370 to 360 million years ago. Well-preserved specimens have been discovered in Morocco, Belgium, Poland, and North America.

Dunkleosteus was probably the top predator in the Devonian seas, reaching lengths of over twenty feet and weighing several tons. Due to its weight, it is unlikely that it was a very fast or maneuverable swimmer, but was capable of taking down even the largest prey items. It boasted an extremely powerful jaw with two pointed plates at the front of the mandibles that worked like a giant chopping block in the absence of teeth. It might have actually been one of the first jawed fish, demonstrating the success that particular evolutionary adaptation had on marine ecosystems. Studies made by the University of Chicago concluded that dunkleosteus had the most powerful bite of any known fish, capable of exerting several thousand pounds per square inch of force. This study took into account the size and shape of the skull and jaws and the musculature that would be needed to move them. This places it on par with other animals with an extremely powerful bite, such as dinosaur therapods, crocodiles, and hyenas. A more recent study conducted by U.S. researchers in 2006 concluded that a lower figure of 1100 pounds per square inch in the jaw was more likely. This still pales the bite strength of hyenas which exert 500 pounds per square inch while crushing bones in their mouth. However, figures for the pressure capability at the tip of the jaw, at the flat slicing plates are as high as 22,000 pounds per square inch!

Due to its size and metabolic requirements, the Dunkleosteus would need to consume copious amounts of feed. Evidence for its large appetite exist in the fossil record, where bones of fish and sharks have been found in the digestive cavity of the gigantic armored fish. Also, it seems possible that dunkleosteus would regurgitate semi-digested remains of its food in order to avoid digesting bone and other tough matter. These fragmentary remains have been found near preserved skeletons of the placoderm. The dunkleosteus and other placoderms are also unique in that they may have been the animals that physically mated as male and female. This technique is used primarily by sharks today in marine environments, while traditional fish fertilize eggs by moving over them and depositing sperm.

Dunkleosteus and the other armored placoderms did not survive past the Devonian. Although placoderms were top predators for nearly fifty million years, other predators such as newly-evolved sharks and marine reptiles would take over the role of top predator of the seas. Many can breathe a sigh of relief that there are no living relatives of placoderms alive in the oceans today.