EVIDENCE FOR A NEOGENE REGIONAL MASS EXTINCTION OF REEF-BUILDING CORALS IN THE TROPICAL AMERICAS

Because of its relative completeness, the geologically recent fossil record provides an excellent opportunity to study the extinction of species. To investigate the nature of Neogene extinctions in reef-building corals, Lyellian percentages were calculated for Miocene to Pleistocene scleractinian faunas of the tropical Americas (n = 47) and the tropical Indo-Pacific region (n = 31). Analysis of the swarm of points for both regions reveals similar average species durations of approximately twelve million years, as well as a ‘standard’ Lyellian curve of background extinction operating throughout most of Neogene time. During Late Pliocene time between two and three million years ago, however, the curve for tropical American species displaces downward relative to the standard curve, suggesting a regional intensification of extinction. Since shallow-water faunas in southern Florida, the Great Bahama Bank, and Jamaica suffered excess extinction close to the Plio-Pleistocene boundary, extinctions must have also occurred during Early Pleistocene time. The extinctions finally subsided by the end of the Middle Pleistocene Subepoch, when Lyellian percentages exceed 90%. Possible causes of this sudden pulse of extinction include climatic cooling, a reduction in upwelling and productivity, and species-area effects associated with sea level regression. Climatic cooling is supported for the following reasons: 1) Accelerated extinction in tropical American coral faunas generally coincides with the initiation of the Northern Hemisphere glaciation, which has been linked to extinctions in marine mollusks and African land mammals among others. 2) A non-random distribution of points between two and three million years ago exhibits a biogeographic pattern in tropical American extinctions with a strong inverse correlation between latitude and survival of stenothermal, warm-adapted coral species. 3) Eustatic changes in sea level fail to explain the lack of heavy extinction among corals in the vast tropical Indo-Pacific region.