(NAS Colloquium) The Future of Evolution (2002) / Chapter Skim
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Lessons from the Past: Evolutionary Impacts of Mass Extinctions
Lessons from the Past: Evolutionary Impacts of Mass Extinctions
Pages 5-10
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From page 5... ...
The best comparisons for predictive purposes therefore will involve factors such as differential extinction intensities among regions, clades, and functional groups, rules governing postextinction biotic interchanges and evolutionary dynamics, and analyses of the factors that cause taxa and evolutionary trends to continue unabated, to suffer setbacks but resume along the same trajectory, to survive only to fall into a marginal role or disappear ("dead clade walking") , or to undergo a burst of diversification.
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From page 6... ...
or the biogeographic fabric of postextinction evolutionary patterns, therefore would be especially valuable with reference to present-day and future processes. Biotic interchanges in the paleontological record, such as the late Cenozoic responses to the joining of North and South America after the final uplift of the Panama Isthmus, or the opening of transpolar interchange between Pacific and Atlantic, clearly document asymmetries in biotic interchanges that correspond to regional differences in extinction intensities (31, 32~.
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From page 7... ...
My preliminary, unpublished analysis suggests that the intervals after mass extinctions tend to be significantly enriched in taxa that failed to cross the next stage boundary, relative to other intervals before the extinction event; in other words more clades that survived a mass extinction tend to dwindle or disappear shortly after the event than would be expected by chance. Also intriguing is the geographic variation in the proportion of dead clade walking taxa across the K-T boundary, with values highest not in North America (which makes an interesting statement on the impact of the greater influx of invaders there—they followed extinctions but did not drive them)
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From page 8... ...
The fossil record shows that destructive and generative aspects of extinction generally operate in different time frames, as many authors have pointed out (2, 41, 68~. The biotic impoverishment and homogenization necessarily precedes the evolutionary response, and there is surprisingly little hard evidence for major evolutionary innovations within a major extinction episode.
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From page 9... ...
Asymmetries in ancient biotic interchange generally appear to reflect geographic differences in extinction intensity. The K-T extinction shows, however, that although biotic interchanges pervade the postextinction world, simple linear relationships can break down to produce unexpected source-sink patterns.
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From page 10... ...
(1994) Systematics and the Fossil Record (Blackwell, Oxford)
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