Phanerozoic extinctions: How similar are they to each other?

Abstract

A brief account of the major Phanerozoic extinction events suggests that each one has a flavor all its own. Major extinction events involving varied combinations of different taxonomic levels, such as many classes, or many orders, or many families, and the varied impacts on community structure in varied combinations are what is referred to here by “flavor”. Most of the evidence discussed is taken from the relatively well sampled, marine, level bottom environment. Recent evidence developed by Kauffman and a few others suggests that extinctions take place over a geologically brief interval of time in which more stenotopic taxa are eliminated, followed by an abrupt termination of the more abundant, higher biomass eurytopes, during community collapse. Adaptive radiations too, appear to take place during a geologically brief interval (up to a few million years) rather than “instantaneously ”in ecologic time (less than a thousand years). This suggests that “instantaneous ”extra-terrestrial events are not likely to have influenced the gradual phase of either extinctions or adaptive radiations in any very important manner, unless they are in need of ecological amplification in order to be recognized. Long term extra-terrestrial events that potentially resulted in terrestrial climatic gradient changes might have been significant. However, the more instantaneous community collapse, high biomass effects, might involve other factors, including certain types of extra-terrestrial events. The decoupling, non-coincidence in time of the extinction events and adaptive radiations in varied parts of the global ecosystem, such as the marine and nonmarine environment, does not support a concept of “instantaneous ”extra terrestrial influences. It is concluded that we still have little understanding of the specifics involved in any major extinction event or adaptive radiation on land or sea. Many of our paleontologic cum geologic data have been collected in such an inadequate manner as to make new sampling mandatory if we are to attain a better understanding of these problems.