ROLE OF TEMPERATURE AND NUTRIENTS IN EXTINCTION OF TURRITELLINE GASTROPODS - CENOZOIC OF THE NORTHWESTERN ATLANTIC AND NORTHEASTERN PACIFIC

Turritelline gastropods (Mesogastropoda, Turritellidae) are common to abundant components in many fossil (Cretaceous, Cenozoic) and Recent marine benthic communities, but the environmental factors affecting their evolution and extinction are poorly understood. This is in large part because today they occur most abundantly in cooler waters associated with upwelling or other high-nutrient conditions, but thermal tolerances and preferences are unclear for extinct turritelline species. Turritellines were diverse and abundant throughout the New World for much of the Cenozoic. Beginning in the early Neogene, through both extinction and range contraction, however, they started to disappear from higher latitudes on both Atlantic and Pacific coasts of North and Central America. The highest rate of extinction took place in the western Atlantic in the Plio-Pleistocene, when almost all turritelline species in this area became extinct. Preliminary comparison of the available stratigraphic record suggests that this paleobiogeographic pattern is not an artefact of the record. This biogeographic shift coincides with a postulated regional mass extinction among all marine mollusks in the western Atlantic at around the same time. Causes for turritelline extinction, however, appear to be more complex than the decline in temperature that is cited most often as the probable cause of the western Atlantic molluskan extinction event. Neogene turritellines in the western Atlantic appear to have been adversely affected by collapse and/or major reorganization of oceanic productivity associated with the formation of the Isthmus of Panama. Nutrients thus may have been more important than temperature change in controlling extinction probability in this group.