Late Devonian Swim

Late Devonian Swim

By: Michael Fouts

July is the time for fireworks, cookouts, swimming pools and, of course, the annual ritual of Shark Week. As you sit on your couch watching helpless seals swimming for their lives and learn about the unnerving ability of the bull shark to swim up freshwater rivers, you may be thankful that you live in Ohio, a state where you won’t need a bigger boat. But 380 million years ago this would not have been the case, because Ohio, or rather the area that would become the Buckeye State, was a much more dangerous place to swim.

A deep, stagnant prehistoric sea covered the state during the later Devonian Period, or 416 million years ago – 359 million years ago. This sea was full of many unique, now extinct, creatures ranging from some of the earliest known shark species to armor plated fish known as arthrodires. In seas so abundant with life there had to exist an apex predator. During the Devonian, the hyper carnivore known as Dunkleosteus terrelli held the heavyweight title of most terrifying fish alive (a title currently being held by Spike the walleye).

Dunkleosteus (named in honor of Dr. David Dunkle, a former curator at the Cleveland Museum of Natural History) was the largest genus of the now extinct group of fish known as arthrodires, a name which means “jointed neck.” Arthrodires were armor-plated, jawed fish that flourished during the Devonian and continued to thrive until they suffered a massive extinction at the end of the period, a run that lasted about 50 million years. The jaws of arthrodires, such as D. terrelli, did not contain teeth. Instead they possessed protruding, sharpened bone plates used to slice through flesh like a knife.

D. terrelli not only had the mouth gear to haunt your nightmares, it also had size to back it up. This was a fish that reached lengths of 20 feet long and is estimated to have weighed in over one ton.

The remains of these massive prehistoric fish have been found in northeastern Ohio. So far only the only fossil evidence we have of D. terrelli are their bony-plated heads, the rest of their bodies have been recreated based on fossil evidence we have from other arthrodires and based upon the measurements we have from heads that have been discovered. Because of this some mystery still surrounds this amazing prehistoric predator. The mass extinction of the arthrodires at the end of the Devonian opened up niches for sharks and other fish to flourish, allowing us Ohioans to enjoy the thrill of Shark Week without any of the terror.

Would you like to see the fossilized remains of D. terrelli? You can visit the Kirtland Hall of Prehistoric Life at the Cleveland Museum of Natural History:

To learn more about Dunkleosteus terrelli please visit:

To learn more about Devonian Ohio please visit:


Posted July 1, 2017

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