Turning Over a New Leaf

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Science  10 Sep 2004:
Vol. 305, Issue 5690, pp. 1535
DOI: 10.1126/science.305.5690.1535c

Plants form the basis of most ecosystems, and understanding their turnover at the Cretaceous-Tertiary boundary is critical for determining the environmental effects of the large asteroid impact that seems to have triggered the mass extinction. Wilf and Johnson have studied in painstaking detail a section in North Dakota that spans the boundary and, when combined with other sections in North America that seemed to bear much of the brunt of the impact, helps document the effects of the extinction and earlier climate changes during the Cretaceous. Analysis of both leaf fossils and pollen shows that in all, about one-third to three-fifths of plant species in North America became extinct at the boundary, a bit lower than most previous estimates. Additional extinction occurred as a result of gradual global cooling during the latest Cretaceous. Most of the survivors were minor contributors to the Cretaceous ecosystem, yet they dominated the subsequent ecosystems in the Tertiary. — BH

Paleobiology 30, 347 (2004).

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