The modularity and development of Cambrian reef ecosystem

The unique diversity of modern reefs is maintained to a significant extent by flame-building organisms which due to their modular habit provide three- dimensional space suitable for tiny niche partitioning. Many principal grou ps of reef-builders in the Phanerozoic history of the Earth demonstrate a r egular pattern of the appearance and progressive development of modularity from low-modular noncommunicating forms to high modular communicating forms that are true colonies. Already the earliest skeletal modular organisms (a rchaeocyaths and other sponges, radiocyaths, coralomorphs, renalcids) show such a pattern. A comparison of Cambrian reef-building organisms with their relatives indicates the superiority of modular forms over solitary ones am ong them. Among advantages of reefal modular organisms over their solitary relatives there are: (1) larger individual size, (2) increased gregarity, ( 3) higher growth rate, (4) increased survivorship, and (5) strengthened anc horing to the substrate. The appearance of true colonies as utterly develop ed modular forms in different evolutionary lines may be evident for indepen dence of development of coloniality and asexual reproduction.