PARSIMONY ANALYSIS OF ENDEMICITY (PAE) OF A LATE ORDOVICIAN FAUNAL MIGRATION EVENT: WHERE DID INVASIVE TAXA ORIGINATE, AND HOW DID THEY GET TO THE CINCINNATI BASIN?

The Late Ordovician strata of the C4 and early C5 sequences near Cincinnati, Ohio record a regional invasion event, the Richmondian Invasion, which introduced over 60 genera into the Cincinnati basin. Prior studies of this time interval using various methods have identified several potential source areas for the invaders; however, the exact timing, pathways taken, and dispersal mechanisms are not fully understood.

In this study, we utilize Parsimony analysis of endemicity (PAE) and similarity indices to examine shifting patterns of endemicity and taxonomic connectivity between tectonic basins in eastern North America (south central and marginal Laurentia) during the C1 to C6 sequences of the Cincinnatian Series. The Cincinnati basin, Upper Mississippi Valley, Anticosti Island, Nashville Dome, and Appalachian basin were stratigraphically correlated using sedimentary analyses from literature. Area cladograms were evaluated to identify dispersal events occurring between sequences by identifying shifts in associations among basins through time. Paleoceanographic conditions within Laurentia were interpreted from stratigraphic information and ocean circulation models and compared to dispersal events to determine mechanisms and pathways of faunal migration.

Analyses recovered a discreet pathway taken by some invasive taxa from Anticosti Island, Canada, into the Cincinnati region. Dispersal occurred from Anticosti Island to the Upper Mississippi Valley during the C2 sequence. Similarity indices support close area relationships between Anticosti Island, the Upper Mississippi Valley, and the Cincinnati basin. Subsequent dispersal occurred from the Upper Mississippi Valley into the Cincinnati basin. Basin infilling led to breaching of major arches between basins and opened additional dispersal pathways. Surface currents and hurricanes moving from the northeast likely contributed to dispersal of organisms from Anticosti Island into surrounding basins. Hypothesized dispersal routes and timing are further supported by examining larval development and transport modes.