Ontogenies and astogenies and their significance in some favositid and heliolitid corals

Abstract

The level of colony integration in tabulate corals is the degree of colony unity with respect to behavior, physiology, and development of individual organs or organ complexes within colonies. These are difficult to assess in fossils, but the level of colony integration can be tested by analyzing ontogenies and astogenies of two common Paleozoic tabulate coral groups, favositids and heliolitids. Favositids have been previously interpreted as highly integrated colonies, but results of the present examination suggest that the level of colony integration in favositids was rather lower than hitherto assumed. The ontogenies and astogenies in favositid colonies are not correlatable; thus, the significance of ontogenetic and astogenetic variations for systematic and phylogenetic resolution in favositids is difficult to assess at present. In contrast, astogenetic developmental sequences are recognized in heliolitids. Ontogenies in heliolitids were subordinated to the astogeny of the colony. This is closely related to the high degree of colony integration with respect to behavior and physiology of individual organs or organ complexes within colonies. Individual corallites were well linked and coordinated so that the whole colony could have functioned as a single individual. As a result, evolution in heliolitids operated at the colony level and by heterochronic (and other) modifications of astogenies rather than of ontogenies.