Remembling a large fish, the Dunkleosteus was an armored variant. It was very large and was not afraid to eat it's own kind as well as sharks. It had large boney teeth that could crush other Dunkleosteus' armor.
Nigel designs a shark cage that allows him to stay safe while the Dunkleosteus swims in the water. While it was able to keep him safe, the predator still dented the cage.