The end-cretaceous mass extinction in the marine realm: year 2000 assessment

The current database indicates that the terminal decline and extinction, or near extinction, of many groups commonly attributed to an asteroid or come t impact at the Cretaceous-Tertiary (K-T) boundary (e.g., ammonites, bivalv es, planktic foraminifera) began during the last 500 k.y. of the Maastricht ian. By the time of the K-T boundary, extinction-prone tropical and subtrop ical marine faunas and floras were almost gone, or had severely reduced spe cies populations struggling to survive, The K-T boundary kill-effect was la rgely restricted to these struggling tropical and subtropical populations t hat accounted for 2/3 of the species among planktic foraminifera, but less than 10% of the total foraminiferal population. No significant extinctions occurred among ecological generalists that dominated across latitudes. No s ingle kill mechanism can account for this mass extinction pattern. The last 500 k.y. of the Maastrichtian were characterized by a series of rapid and extreme climate changes characterized by 3-4 degreesC warming between 65.4 and 65.2 Ma, major volcanic activity between 65.4 and 65.2 Ma, a spherule-p roducing event between 65.3 and 65.2 Ma, and an impact at the K-T boundary (65.0 Ma). All of these events caused major environmental perturbations and biotic stresses that resulted in severe reductions in species populations and extinctions that culminated at the K-T boundary. The mass extinction pa ttern, and the parallel environmental changes during the last 500 k.y. of t he Maastrichtian, suggest that both long-term (climate, sea-level) and shor t-term (impact, volcanism) events contributed to the K-T boundary mass exti nction. (C) 2001 Elsevier Science Ltd. All rights reserved.