CHARACTER STATE EVOLUTION IN A NEW PHYLUM: RADIATION OF BRYOZOA DURING THE EARLY TO MIDDLE ORDOVICIAN, WITH A DAPINGIAN TO DARRIWILIAN TRANSITION
Species-level occurrences of seven fundamental parameters that control colony growth and form (orientation, dimensions of growth, feeding currents, layers of zooecia, substrate relationships, space utilization) were coded for all known Early to Middle Ordovician taxa (179 species, 78 genera, 34 families) through 11 time slices. Bryozoan taxonomic and growth habit richness increases slowly through the early Ordovician (Tremadocian 1b to Dapingian 2c). But there is a marked change in both richness and the relative importance of fundamental growth characters, beginning at the transition from the Early to Middle Ordovician (Dapingian 2c to Darriwilian 3a). Many of these trends continue to the end of the Middle Ordovician. The timing of this change predates similar trends in geochemistry (∂C13, atmospheric oxygen) and diversity of other groups (brachiopods and blastozoans). Changes among bryozoan growth habit features and fundamental changes in features of carbonate substrates at the Early to Middle Ordovician transition, may be related to an increase in availability of firm and hard substrates substrates.