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Paper No. 84-18
Presentation Time: 9:00 AM-5:30 PM
ARE THERE TRENDS IN BIVALVE ORNAMENTATION THROUGHOUT THE CRETACEOUS?
Evolutionary trends in morphology may serve as indicators of interactions between predators and their prey. During the Mesozoic Marine Revolution, bivalves are thought to have faced increased predation from shell-crushing crustaceans, drilling gastropods and teleost fishes, particularly near the end of the Mesozoic. Experiments have shown that ornamentation features on bivalves, such as ribbing, folds and spines, can be effective against predation. To test the hypothesis that bivalve ornamentation increased throughout the Cretaceous in response to diversification of predators, we assembled a database scoring the ornamentation (presence and strength of ribs, folds, spines, tubercles, smoothness and auricles) of ~500 Cretaceous bivalve species. Epifaunal bivalves show no evidence of increasing ornamentation throughout the Cretaceous, while ornamentation of infaunal bivalves may decrease slightly, perhaps indicating increased infaunalization. During most Cretaceous stages, there is little difference in the degree of ornamentation between extant and newly originating genera, and the degree of ornamentation rarely has a significant influence on extinction risk. Combined with other analyses of Jurassic mollusks, our results suggest that any morphological responses to predator diversification among bivalves were idiosyncratic and lineage-specific or delayed until the Cenozoic.