Dunkleosteous was the very first apex predator with bones. This giant armor-plated fish is very well-known to the public because of its mouth. Many people think those sharp things in its mouth are its teeth, but they're not. They're actually extensions of jaw bone. What would happen is when the fish closed its mouth, the extensions would act like scissors so they're alway sharp. Dunkleosteous had such powerful jaws it could bite through the rock-hard armor of other armor-plated fish. There's even evidence that Dunkleosteous ate eah other. Some fossils of Dunkleosteous armor show signs of bite marks that aren't healed and the jaws of Dunkleosteous are a perfect fit. There's another reason why you don't want to invite Dunkleoseous to dinner. Some fossils show that Dunkleosteous had horrible table manners. The fossils show Dunkleosteous often tried to make itself barf. However, Dunkleosteus may have barfed often to get rid of pieces of armor it can't digest.