Predation is an important factor in the food web of living organisms. Prey-predator relationships are delicately balanced and over a short period may greatly modify populations and communities. Whereas evidence of predation amongst living organisms is obvious, evidence from fossil assemblages is difficult to document even though predation must have been occurring continuously. Only rarely does a paleontologist see direct evidenoe of predation such as the mosasaur bites on an ammonoid shell described by Kauffman and Kesling (1960).