Dunkleosteus terrelli, an extinct species of the order Arthrodira, class Placodermi, was an apex predator in the marine environment during the Upper Devonian, probably cruising the seas of North America and Eurasia at that time ⁴⁾.

Most species of the placoderms had dorsoventrally compressed body forms and poorly developed heterocercal tails so they have been interpreted as bottom-dwellers and swimmers using undulation of their bodies ³⁾.

However, Dunkleosteus is oval in cross-section ³⁾. In addition, the evidence regarding the environment in which the fossils were producted suggests that Dunkleosteus was not a benthic animal ³⁾.

The total body length, previously estimated 4.5-6 metres. However, a new model based on the ecomorphological approach estimats to be up to 8.79 metres, and also predicts the caudal fin having well-developed ventral lobe, high heterocercal and hypocercal angles, narrow peduncle and wide span, suggesting Dunkleosteus terrelli was a good swimmer ⁴⁾.

Dunkleosteus had a bladed jaws with a well-developed anterior cusp that allowed it to suction when capturing prey, just as modern fishes do ^{1, 2)}. The bite force was extraordinary strong, and greater than those of most modern mammalian predators ^{1), 2)}.

These characters suggest that Dunkleosteus could penetrate protective armor, such as cuticle or dermal bone, allowing this apex predator to potentially eat anything in its ecosystem, including other placoderms ^{1), 2)}.

Some species of the placoderms from the Upper Devonian formation had embryos inside their body, suggesting some placoderms were internal fertilization and vivoparous ⁵⁾. But, the direct evidences that Dunkleosteus terrelli also was vivoprous have not been found yet ³⁾.