Slow-moving grazers wander over the mats, consuming this rather uniform resource. Other animals feed without moving. These animals then become a new kind of resource; they are big concentrations of nutritious carbon compounds. Nutrition is now less spread out than it was. It exists in patches. These animals might first have only been consumed by others after they had died. But this soon changed. Scavenging became predation. If the fossil record is taken at face value,
