Competitive displacement among post-Paleozoic cyclostome and cheilostome bryozoans.

Encrusting bryozoans provide one of the few systems in the fossil record in which ecological competition can be observed directly at local scales. The macroevolutionary history of diversity of cyclostome and cheilostome bryozoans is consistent with a coupled-logistic model of clade displacement predicated on species within clades interacting competitively. The model matches observed diversity history if the model is perturbed by a mass extinction with a position and magnitude analogous to the Cretaceous/Tertiary boundary event, Although it is difficult to measure all parameters in the model from fossil data, critical factors are intrinsic rates of extinction, which can be measured. Cyclostomes maintained a rather low rate of extinction, and the model solutions predict that they would lose diversity only slowly as competitively superior species of cheilostomes diversified into their environment. Thus, the microecological record of preserved competitive interactions between cyclostome and cheilostome bryozoans and the macroevolutionary record of global diversity are consistent in regard to competition as a significant influence on diversity histories of post-Paleozoic bryozoans.

Decoupled temporal patterns of evolution and ecology in two post-Paleozoic clades.

Counts of taxonomic diversity are the prevailing standards for documenting large-scale patterns of evolution in the fossil record. However, the secular pattern of relative ecological importance between the bryozoan clades Cyclostomata and Cheilostomata is not reflected fully in compilations of generic diversity or within-fauna species richness, and the delayed ecological recovery of the Cheilostomata after the mass extinction at the Cretaceous-Tertiary boundary is missed entirely. These observations demonstrate that evolutionary success and ecological dominance can be decoupled and profoundly different, even over tens of millions of years.

Coral-bryozoan mutualism: structural innovation and greater resource exploitaton.

Shell-encrusting species of the coral Aulopora and the bryozoan Leioclema changed ecological pgilds and escaped limits imposed by substrate size through mutstic intergrowth during the Early Devonian. Where colonies of these species intergew, they produced upright, arborescent masses consisting of sparsely branched uniserial Aulopora sp. entirely covered, except for calyx openings, by a thin encrustation of Leioclema sp. These interrowts appear to constitute a mutualistic association with benefits induding escape from limited space on the substratum into a higher tier of suspension feeders, as well as more modules per colony. Such mutualism between benthic modular competitors may have developed more readily than assocations between solitary competitors.

Bryozoan monticules: excurrent water outlets?

Monticules, regularly arranged modified areas on Paleozoic Bryozoa, may represent regions from which water currents produced by lophophores of adjacent feeding zoids escaped. Such circulation Patterns have been observed Recent forms.