ECOLOGICAL SHIFT IN PROETID AND PHACOPID ASSOCIATION THROUGH THE DEVONIAN

Trilobites, once major prolific members of benthic communities in the Paleozoic, were reduced to one order, Proetida, following the Devonian extinction events. Curiously, proetid trilobites were riveled in diversity by other trilobites, such as phacopids, throughout the Devonian. Phacopids especially surpassed proetids in diversity for much of the mid-to-late Devonian before complete extinction. Despite the differing selection pressures of each group being well studied separately, the two orders have not been examined together to determine if any co-occurrence transpired across this interval of change. In order to tease apart any potential biotic interactions between these two groups, a co-occurrence analysis was conducted. This co-occurrence analysis examined trilobite relationships across space in two ways: biogeographic regions across the Devonian world and position on the continental shelf. I found that proetids and phacopids did not overlap biogeographically much across the Devonian but, when there was overlap, they did overlap on continental shelf space in the late Devonian. Both groups, considered “morphologically conservative” in comparison to other trilobites, may have resembled each other morphologically (e.g., eye-less) due to similar overlap in continental shelf space (e.g., deep benthic). More work needs to be done to determine the potential for biotic interactions amongst major trilobite clades in the Paleozoic.