100-MILLION YEARS OF COMPETITIVE INTERACTIONS BETWEEN BRYOZOAN CLADES- ASYMMETRICAL BUT NOT ESCALATING

Direct evidence of competition is seldom available from the fossil rec ord. Overgrowth relationships of encrusting marine organisms constitut e an exception but have previously been reported in only temporally an d geographically local occurrences. Results of overgrowths between mem bers of two bryozoan clades, the Cyclostomata and the Cheilostomata, h ave been compiled for faunas distributed through the past 100 Myr. The cheilostomes have consistently out-competed the cyclostomes, with app roximately 66% overgrowth success through the entire interval. This di fference in success in direct interactions along with the Mid-Cretaceo us rapid radiation of cheilostomes is interpreted as a factor in the M id- to Late Cretaceous reversal from the previous diversification to s tasis or gradual decline of cyclostome diversity.