Dunkleosteus could open its mouth in one-fiftieth of a second, which would have caused a powerful suction that pulled the prey into its mouth, a food-capture technique used by many fish today.
The discovery of Dunkleosteus armor with unhealed bite marks strongly suggest that they cannibalized each other when the opportunity arose. Frequently, fossils of Dunkleosteus are found with boluses of fish bones, semi-digested and partially eaten remains of other fish. As a result, the fossil record indicates that it may have routinely regurgitated prey bones rather than digest them.
Dunkleosteus, like most other placoderms, may have also been among the first vertebrates to internalize egg fertilization, as seen in some modern sharks.
Morphological studies done on the "jaw bones" (inferognathals) of juvenile and adult Dunkleosteus suggest that Dunkleosteus went through a change in jaw morphology and diet as it aged. Juveniles had stiffer jaws more similar to Coccosteus, and appear to have fed on various soft-bodied aquatic animals. The jaws of adults were more flexible to hold struggling prey, and were well equipped to bite through the bony armor of hard-bodied animals like other placoderms.
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