REGIONAL EXTINCTION OF, AND SUBSEQUENT RECOLONIZATION BY, TURRITELLINE GASTROPODS IN THE U.S. GULF COASTAL PLAIN FOLLOWING THE K-PG MASS EXTINCTION

Gastropods of the genus Turritella sensu lato are abundant and diverse in many benthic marine communities in the Late Cretaceous and Early Paleocene worldwide, including the U.S. Gulf Coastal Plain (GCP). Strictly using described species names, very few are known to have survived across the K-Pg boundary globally and none are documented as having survived that mass-extinction in the GCP itself. Given that no more than 100,000 years separates the recorded presence of turritellines in latest Maastrichtian and earliest Danian strata, there exist two possibilities regarding the ancestry of the younger group: 1) all Maastrichtian GCP turritellines became extinct and were quickly replaced by unrelated immigrant species from elsewhere, or 2) some Maastrichtian GCP species survived the extinction in undocumented local refugia and then quickly evolved into descendant Danian species. No phylogenetic analysis has ever been done on these species, but preliminary results of just such an analysis suggest that both of these phenomena may have occurred: some Danian GCP species may be close relatives of Maastrichtian GCP species, while others have closest relatives elsewhere. Investigation of Turritella protoconchs suggests that most of these taxa had planktonic larvae, which would have facilitated broad and rapid dispersal via the oceanic circulation system in the millennia following the K-Pg extinction, providing a likely mechanism for external recolonization of the GCP alongside any currently-unknown, locally-surviving lineages that remained in the region. If confirmed, these results point to the importance of both regional extirpation and refugia in patterns of recovery from mass extinction.