There is no doubt that competition occurs, but less is known about the strength and importance of competition affecting ecosystems. The latter is not easy to get at for living organisms because the role of each organism in the ecosystem needs to be well-known. It is even more difficult for fossil ecosystems because the diet is not fully understood for each species and not all animals have the same preservation potential. Nevertheless, paleontologists have attempted to find evidence for competition between taxa. For example, they have investigated the diversity and abundance through time of two groups thought to have competed with each other by having lived at about the same time and place and having had a similar diet. For example, Sepkoski and colleagues (2000) showed that cyclostome bryozoans became much more diverse in the Cretaceous and Cenozoic, while cheilostome bryozoan diversity declined. Strong competition between these two groups with cyclostomes as the winner is an explanation for this pattern.
