Date of Completion
Janine Caira, Lisa Park Boush
Field of Study
Ecology and Evolutionary Biology
Master of Science
Brachiopods have commonly been considered more important than bivalves in Paleozoic ecosystems due to their greater global diversity and greater abundance in many fossil assemblages. New sampling-standardized diversity curves verify that brachiopods were more diverse than bivalves at the global level in the Paleozoic; they declined in the Permian-Triassic extinction, largely recovered, then faded away later in the Mesozoic. However, the subordinate ecological status of bivalves within local Paleozoic ecosystems has been challenged on two fronts. First, bivalve abundance may be underestimated due to preferential dissolution of aragonitic shells. Second, bivalve contribution to ecosystem function may be underestimated by abundance or diversity data because they tend to have greater biomass and energy use than brachiopods. Here, I compare the relative importance of bivalves and brachiopods in an exceptionally preserved fauna from the Middle Pennsylvanian Breathitt Formation of Kentucky in which aragonitic bivalves are preserved as shells, not molds. I use four metrics of ecological importance – abundance, shell volume, biomass and energy use. Brachiopods outnumbered bivalves and had greater total shell volume, though the two taxa were roughly equivalent in total biomass and energy use. By all four metrics, brachiopods were more important as suspension feeders. The importance of brachiopods relative to bivalves was underestimated when occurrence-level data were used instead of abundance data, suggesting caution in interpreting global trends based on occurrences. Globally, the two taxa were fairly similar in diversity in the Pennsylvanian, so brachiopods may have been more important relative to bivalves at other times in the Paleozoic when their diversity was greater.
Hsieh, Shannon (Shin-nan), "The Ecological Importance of Brachiopods versus Bivalves in the Paleozoic: Taphonomy, Biomass, and Energy use" (2015). Master's Theses. 852.