Source: Bestiary 6, pg(s). 129
A dunkleosteus is a large predatory fish that can exceed 30 feet in length at full growth. In addition to their size, they are physically distinguished by the armor plating covering their heads and by mouths dominated by bony, tooth-like plates. They are capable of opening their jaws in a fraction of a second, creating an inward rush of water; when hunting, they use this to suck prey into their mouths. They are primarily marine animals, but are known to swim into river estuaries to pursue possible prey.
- Dunkleosteus (real-life prehistoric animal) on Wikipedia