The massive placoderm Dunkleosteus was one of the most fearsome and largest prehistoric fish to inhabit the ancient oceans. Existing during the Late Devonian period, approximately 382 to 358 million years ago, this creature represented an early peak in vertebrate evolution. Understanding what Dunkleosteus ate requires examining the scale of the animal, the mechanics of its extraordinary jaw, and the rare fossil evidence that hints at its preferred prey.
The Armored Giant: Context and Scale
This prehistoric fish belonged to the extinct class Placodermi, or “plate-skinned” fish, which were dominant throughout the Devonian period. The largest species, Dunkleosteus terrelli, is estimated to have reached lengths between 11 and 16 feet, though some historical estimates suggested lengths up to 30 feet. This size made it one of the largest marine vertebrates of its time.
The most distinguishing feature of the Dunkleosteus was the thick, bony armor plating that covered its head and the front third of its body. This heavy plating is the part most commonly preserved as a fossil and gave the creature a tank-like appearance, though its body was likely more streamlined. The armor provided protection, likely against intraspecies conflict or the crushing pressures of the deep ocean. The Dunkleosteus was the undisputed top predator of the Late Devonian seas.
Jaw Mechanics: How the Dunkleosteus Ate
The feeding mechanism of Dunkleosteus allowed for both rapid capture and immense crushing force. This placoderm lacked true teeth and instead possessed two pairs of sharp, bony plates extending from its skull and lower jaw, forming a beak-like structure. These bony plates acted like self-sharpening blades, continually grinding against each other as the jaws opened and closed.
The skull and jaw system was powered by a unique four-bar linkage mechanism connecting the skull, thoracic shield, and jaw muscles. This specialized system provided a high speed of jaw opening, enabling the fish to quickly expand its gape. This rapid expansion created a vacuum, allowing the Dunkleosteus to use suction feeding to draw in evasive prey. The entire strike could take as little as 20 milliseconds.
Once the prey was drawn in, the jaw-closing muscles delivered one of the most powerful bites in vertebrate history. Modeling suggests a maximal bite force of over 4,400 Newtons (nearly 1,000 pounds) at the jaw tip. This force, focused onto the sharp edges of the bony plates, generated extremely high local bite stress. The combination of suction and immense bite force allowed Dunkleosteus to catch fast-moving prey and penetrate thick protective armor.
The Menu: What Fossil Evidence Reveals
The specialized nature of the Dunkleosteus jaw suggests a diet composed of the largest and most heavily armored creatures in the Devonian seas. Paleontologists rely on rare fossilized stomach contents, coprolites (fossilized waste), and wear patterns on the bony plates to reconstruct its menu. The jaw plates were specifically adapted to puncture and fragment hard materials, such as dermal bone and cuticles.
Specific prey items included other placoderms, whose armored bodies required significant crushing power to penetrate. Evidence suggests it regularly consumed early, fast-swimming sharks, such as the genus Orodus. The diet also extended to thick-shelled invertebrates like ammonites, which are cephalopods with coiled, hard shells.
Wear patterns indicate a shift in diet from juvenile to adult. Younger Dunkleosteus likely consumed smaller, softer-bodied prey, while adults focused on larger, more heavily armored targets. Direct fossil evidence, such as bite marks on the armor of other Dunkleosteus specimens, suggests cannibalistic behavior, possibly when food sources were scarce.
The Mystery of Digestion
The crushing and shearing action of the Dunkleosteus jaw was effective for fragmenting prey, but the creature lacked the grinding teeth necessary for complete digestion of bone. This anatomical limitation is solved by the fossil record, which contains boluses—masses of fish bones and other partially digested, hard remains—found alongside Dunkleosteus fossils.
These boluses suggest that Dunkleosteus swallowed large portions of its prey whole or in massive chunks, processing only the soft tissue. The indigestible, heavily calcified components, such as armored plates and skeletal remains, would then have been regurgitated in a pellet-like form. This behavior is seen in modern animals, such as certain sharks and owls, which similarly expel the unwanted, hard parts of their meals.