Dunkleosteus

Dunkleosteus terrelli is Ohio's official state fossil fish, designated in 2021. It was a placoderm — a heavily armored fish — and one of the largest predatory fish that ever lived. The armored head and shoulder shield are well preserved in the Late Devonian Cleveland Shale of northeastern Ohio, and the Cleveland Museum of Natural History holds the most complete collection of Dunkleosteus material in the world.

Dunkleosteus terrelli reached up to 20 feet in length. The front half of the body was encased in thick interlocking bony plates that formed an armored head and shoulder shield. Instead of teeth, it had two pairs of sharp bony shearing plates that worked like scissors, capable of cutting through the armor of other fish. Studies of its jaw mechanics suggest one of the most powerful bites of any fish, living or extinct.

Dunkleosteus was an apex predator of the Late Devonian seas, hunting sharks, other armored fish, and large cephalopods. The back half of its body was not armored and rarely preserves, which is why size estimates rely on proportions from the skull. It went extinct about 360 million years ago during the Late Devonian mass extinction, one of the five largest extinction events in Earth's history.

The first Dunkleosteus terrelli specimen was found near Lorain, Ohio in 1867 by Jay Terrell, whose name the species bears. The genus was named for David Dunkle, a paleontologist at the Cleveland Museum of Natural History who studied the species extensively in the mid-20th century. The Cleveland Shale, which outcrops along river valleys and road cuts in northeastern Ohio, has produced more Dunkleosteus skulls than any other location in the world.

Ohio designated Dunkleosteus terrelli as its state fossil fish in 2021, a campaign supported by students and scientists who argued the animal was as iconic to Ohio as any symbol the state had. The designation added a second official state fossil alongside Isotelus maximus, the state fossil invertebrate designated in 1985.

The Cleveland Shale outcrops in Cuyahoga, Lorain, and Erie counties in northeastern Ohio, wherever the Rocky River, Cuyahoga River, and their tributaries cut through Devonian bedrock. Road cuts and riverbank exposures throughout the Cleveland metropolitan area have produced Dunkleosteus skull plates and shoulder armor for over 150 years.

The Cleveland Museum of Natural History holds the definitive Dunkleosteus collection, including several mounted skull reconstructions. It is the best public site to see the animal up close. The Devonian outcrops along the Rocky River in the Cleveland Metroparks are accessible to collectors and are among the most productive public fossil sites in northeastern Ohio.