RESOLVING MOSASAUR (DIAPSIDA, SQUAMATA) EXTINCTION ACROSS THE ATLANTIC

Mosasaur remains are abundant components of Maastrichtian marine shelf faunas from the Mid-Atlantic region of North America (New Jersey and Maryland), the Mons Basin in Belgium, and the Maastricht area of the Netherlands and nearby Belgium. As such, these large, marine-adapted apical predatory lizards of the Late Cretaceous constitute an ideal test of extinction scenarios for marine vertebrates at the K-T boundary. Fluxes in mosasaur generic richness through geologic time may be used to select among competing models of extinction.

To determine mosasaur richness through the Maastrichtian, we tallied reliably identified (genus-level) and stratigraphically well-documented specimens from lithologic units in the above localities. Invertebrate and nannofossil correlations, coupled with sequence stratigraphy and geochronology permitted assignments of the specimens into three trans-Atlantic stratigraphically correlated assemblages (SCAs). Rarefaction analysis of richness per SCA in our database of 270 mosasaur specimens (minimum number of 85 individuals) demonstrates that mosasaur richness remained statistically unchanged throughout the Maastrichtian, and that their extinction took place within the final ~200 ka of the Maastrichtian. These results are incompatible with long-term extinction scenarios, such as changes to community structure or habitat reduction (e.g., eustatic sea level fall). The results are, however, compatible with geologically instantaneous extinction hypotheses, including bolide impact at the end of the Cretaceous. The extinction of mosasaurs was likely brought about by a collapse of the primary production-dependant marine food web over which the mosasaurs dominated.