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Proterozoic and early Cambrian protists: evidence for accelerating evolutionary tempoIn rocks of late Paleoproterozoic and Mesoproterozoic age (ca. 1700-1000 million years ago), probable eukaryotic microfossils are widespread and well preserved, but assemblage and global diversities are low and turnover is slow. Near the Mesoproterozoic-Neoproterozoic boundary (1000 million years ago), red, green, and chromophytic algae diversified; molecular phylogenies suggest that this was part of a broader radiation of "higher" eukaryotic phyla. Observed diversity levels for protistan microfossils increased significantly at this time, as did turnover rates. Coincident with the Cambrian radiation of marine invertebrates, protistan microfossils again doubled in diversity and rates of turnover increased by an order of magnitude. Evidently, the Cambrian diversification of animals strongly influenced evolutionary rates, within clades already present in marine communities, implying an important role for ecology in fueling a Cambrian explosion that extends across kingdoms.
Document ID
20050000321
Document Type
Reprint (Version printed in journal)
Authors
Knoll, A. H. (Botanical Museum, Harvard University Cambridge, MA 02138)
Date Acquired
August 22, 2013
Publication Date
July 19, 1994
Publication Information
Publication: Proceedings of the National Academy of Sciences of the United States of America
Volume: 91
Issue: 15
ISSN: 0027-8424
Subject Category
Exobiology
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Exobiology
Review
Review, Tutorial