Dunkleosteus terrelli (Newberry, 1873) - model of a fossil fish skull from the Devonian of Ohio, USA. (public display, Cleveland Museum of Natural History, Cleveland, Ohio, USA)

The placoderms are a group of extinct, mostly predatory fish that existed during the Middle Paleozoic (Silurian and Devonian). The most famous placoderm was Dunkleosteus, which was named after David Dunkle, an Ohio paleontologist. It was not a shark - it had a bony skull, a neck joint, and remarkably, the jaws lacked true teeth. Instead, the jawbones were sharp-edged and pointed.

From museum signage: Dunkleosteus terrelli Giant fish found in the Rocky River Valley. Dunkleosteus is the most commonly collected armored fish of the Ohio Shale. This is perhaps due to the massiveness of its dermal bones which resisted erosion longer than the thinner and more delicate elements of other genera.

Classification: Animalia, Chordata, Vertebrata, Placodermi, Arthrodira, Dunkleosteidae

Stratigraphy: Cleveland Shale Member, upper Ohio Shale, Famennian Stage, upper Upper Devonian

Locality: northeastern Ohio, USA

See info. at: