National Academies Press: OpenBook

Effects of Past Global Change on Life (1995)

Chapter: ABSTRACT

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Suggested Citation:"ABSTRACT." National Research Council. 1995. Effects of Past Global Change on Life. Washington, DC: The National Academies Press. doi: 10.17226/4762.
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Page 184

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GLOBAL CLIMATIC INFLUENCE ON CENOZOIC LAND MAMMAL FAUNAS 184 11 Global Climatic Influence on Cenozoic Land Mammal Faunas S. David Webb And Neil D. Opdyke University of Florida ABSTRACT The Cenozoic succession of continental mammalian faunas reflects the climatic shift from a "greenhouse" to an "icehouse" world. In midcontinental North America, where the most nearly complete record of terrestrial biotic succession has been assembled, floral and faunal evidence chronicle a broad progression of biome change from tropical forest to savanna to steppe. Thanks to improved land mammal chronologies, the tempo of faunal turnover is now seen to be strikingly syncopated. Stately chronofaunas, made up of stable sets of slowly evolving taxa, persist on the order of 107 yr. Chronofaunas are terminated by rapid turnover episodes in which some native taxa experience rapid evolutionary rates and other taxa appear as intercontinental immigrants. We focus here on pulses of immigration and their correlation with major climatic shifts. The Tertiary record of North American land mammals registers a total of 140 immigrant genera. The chronology of most immigrant arrivals can be placed within the nearest million years (m.y.) or less. The pattern of immigration is decidedly nonrandom, with the largest two episodes involving 15 and 14 genera each within about 1 m.y. We categorize immigrant arrivals into first-, second-, and third- order episodes, with the first consisting of at least nine genera within less than 1 m.y. The seven first-order episodes occur at 58.5, 57, 40, 20, 18.5, 5, and 2.5 m.y. ago (Ma). The first-order episode at ~40 Ma may represent an artifact due to tallying at the end of a long interval of poorly fossiliferous deposits (Uintan). A striking generalization is that the six other first-order episodes occur as three pairs separated by only about 2 m.y. Review of land mammal immigration and rapid turnover episodes on other continents tends to confirm the "universality" of major immigration episodes at ~20, ~5, and ~2.5 Ma. We consider two hypotheses that might causally relate high intercontinental immigration rates to global climate change. The first proposes a correlation between high immigration rates and the availability of land bridges during low sea-level intervals. In this

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What can we expect as global change progresses? Will there be thresholds that trigger sudden shifts in environmental conditions—or that cause catastrophic destruction of life?

Effects of Past Global Change on Life explores what earth scientists are learning about the impact of large-scale environmental changes on ancient life—and how these findings may help us resolve today's environmental controversies.

Leading authorities discuss historical climate trends and what can be learned from the mass extinctions and other critical periods about the rise and fall of plant and animal species in response to global change. The volume develops a picture of how environmental change has closed some evolutionary doors while opening others—including profound effects on the early members of the human family.

An expert panel offers specific recommendations on expanding research and improving investigative tools—and targets historical periods and geological and biological patterns with the most promise of shedding light on future developments.

This readable and informative book will be of special interest to professionals in the earth sciences and the environmental community as well as concerned policymakers.

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