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Unformatted text preview: Dynamics of origination and extinction in the marine fossil record John Alroy* National Center for Ecological Analysis and Synthesis, University of California, 735 State Street, Santa Barbara, CA 93101 The discipline-wide effort to database the fossil record at the occurrence level has made it possible to estimate marine inverte- brate extinction and origination rates with much greater accuracy. The new data show that two biotic mechanisms have hastened recoveries from mass extinctions and confined diversity to a relatively narrow range over the past 500 million years (Myr). First, a drop in diversity of any size correlates with low extinction rates immediately afterward, so much so that extinction would almost come to a halt if diversity dropped by 90%. Second, very high extinction rates are followed by equally high origination rates. The two relationships predict that the rebound from the current mass extinction will take at least 10 Myr, and perhaps 40 Myr if it rivals the Permo-Triassic catastrophe. Regardless, any large event will result in a dramatic ecological and taxonomic restructuring of the biosphere. The data also confirm that extinction and origination rates both declined through the Phanerozoic and that several extinctions in addition to the Permo-Triassic event were particu- larly severe. However, the trend may be driven by taxonomic biases and the rates vary in accord with a simple log normal distribution, so there is no sharp distinction between background and mass extinctions. Furthermore, the lack of any significant autocorrelation in the data is inconsistent with macroevolutionary theories of periodicity or self-organized criticality. biodiversity u macroevolution u mass extinction D ecades of literature on large-scale taxonomic diversification and extinction patterns have hinged on compilations that record little more than first and last appearances of families or genera. Key examples include Sepkoski’s compendia of marine families (1) and genera (2) and the Fossil Record 2 database of marine and continental families (3). Numerous patterns of widespread scientific and public interest have been identified on the basis of the older compilations, such as the identity of the five largest mass extinctions (4, 5), a gradual decline of extinction rates throughout the entire Phanerozoic (4), and possible cycles in extinction rates (6). A complete reevaluation of these hypoth- eses is now made possible by the maturation of the Paleobiology Database, a relational, web-based, and much more detailed resource created by and for the paleontological community (7). Arguably, the most enduring and biologically important ques- tion these data can answer is whether global biodiversity is saturated (1, 8, 9). If so, then ecological interactions, such as competition and predation, must control rates of speciation and extinction (10–12). Speciation rates must be lower or extinction rates must be higher than they would be without these interac-...
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This note was uploaded on 06/08/2011 for the course PCB 4674 taught by Professor Baer during the Fall '08 term at University of Florida.
- Fall '08