The tempo of mass extinction and recovery: the end-Permian example.

Abstract

Mass extinctions are brief episodes of greatly increased extinction, commonly affecting both marine and terrestrial species. Since the origin of animals some 600 million years ago, there have been at least six major mass extinctions. The disappearance of the dinosaurs during the end-Cretaceous mass extinction 65 million years ago is perhaps the best known event, but the end-Permian ( ca. 251 million years ago) extinction was, without question, the most profound. Although extinctions (often called background extinctions) have occurred throughout Phanerozoic history, they are distinct from mass extinctions. Mass extinctions and recoveries have played a fundamental role in animal evolution, comparable to natural selection, because they may trigger the demise of dominant species and massive reorganization of entire ecosystems. Thus understanding mass extinctions and their recoveries is critical for further developing models of evolutionary process. In particular, we seek to answer the following questions: ( i ) How rapidly do these extinction events occur? ( ii ) What caused them, and is there a single mechanism for all extinctions? ( iii ) What became extinct, what survived, and why? ( iv ) How did life recover in the aftermath of these events? We have chosen to concentrate on the end-Permian extinction because it eliminated at least twice as many species, over 85% of species in the oceans, as the next largest extinction. This event triggered the most widespread reorganization of ecosystems and animal diversity in the past 500 million years and is largely responsible for much of the structure marine ecosystems today. Out of the devastation of the extinction, the Paleozoic marine communities dominated by sessile filter-feeding clades such as brachiopods and stalked echinoderms were replaced by a new suite of communities. These new communities included more mobile and burrowing groups and a higher percentage of predators. In addition, after the postextinction recovery, we see the rise of both …