Many creatures survived and proliferated during a time of drastic environmental change. Giant mollusks appeared and became the dominant species of the Cambrian Period. Arthropods, including trilobites, evolved into various species. “Mullokunmingia” was one of the first fish, and other fish began to appear in the early Ordovician period. After the evolution of fins, hard jaws, swim bladders, these fish could more effectively attack and kill their prey, and they became the dominant species in the Devonian seas.