PHYLOGENETIC AND BIOGEOGRAPHICAL PATTERNS OF PROETID TRILOBITES ACROSS THE DEVONIAN-CARBONIFEROUS BOUNDARY

The end-Devonian is known to have had ecological and environmental changes which caused losses (and otherwise impacted radiations) of prolific Paleozoic groups such as trilobites. Among trilobites, proetids were the last, a proverbial “Dead Clade Walking” following the end-Devonian event(s). It has been suggested that the end-Devonian depletion event(s) were driven not just by elevated extinction, but also by depressed speciation rates facilitated by interbasinal species invasions in which alpha diversity was maintained with immigrants rather than new species. A corollary hypothesis is the persistence of proetid trilobites through the end-Devonian (and which therefore affected the possible radiations of the Early Carboniferous) was partially due to their increased immigration or expansion of geographic range, a process which may have impacted other species. To examine this, I performed a Bayesian analysis of biogeography of proetid trilobites from the beginning of the Devonian to the early Carboniferous. This type of analysis incorporates both a paleogeographic (i.e., discrete presence or absence data) and a biological (i.e., a phylogeny) component to understand how certain clades change their range over their history. The phylogeny was global and included proetids from literature and collections. I performed a separate Bayesian analysis utilizing the proetid phylogenetic tree and presence/absence data of these proetids per biogeographic province based on paleolatitude and paleolongitude. Paleoenvironment (e.g., position on continental shelf) of proetids was also noted for interpretation. I found that proetids did indeed expand their geographic range size, though mostly in higher latitudes. Proetids in lower latitudes either went extinct or moved northwards, homogenizing a lot of mid-latitude communities. Future directions will incorporate the findings in this study and examine expansion of proetid geographic range size potentially impacted other continental shelf species.