Ontogeny in animal colonies: a persistent trend in the bryozoan fossil record

The principal modes of zooid and colony growth in encrusting cheilostome bryozoans have undergone a major evolutionary transition during the last 100 million years. Comparisons of species within successive North American fossil faunas reveal a persistent trend in which one mode of growth is gradually supplanted by another. Ecological evidence from living faunas and the polyphyletic nature of this trend suggest that the transition has adaptive significance.