The organisms of the Waynesville Formation (Ordovician--Cincinnatian) represented life in an ocean devoid of fish. At that point, 445 million years ago, fish did not fill predatory niches in the oceans, as they often have done since jawed varieties evolved. Instead, invertebrates such as trilobites, cephalopods, and eurypterids evolved mechanisms for predation. For example, the trilobite Isotelus developed a forked hypostome (mouthpart) thought to have been used in cutting prey. Many trilobites also developed spines or the ability to enroll in order to protect themselves from predators. The evolution of predatory habits and anti-predation mechanisms in trilobites may be one reason they were among the most successful groups of organisms to inhabit the earth.