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Title:
Disparate Rates, Differing Fates: Tempo and Mode of Evolution Changed from the Precambrain to the Phanerozoic
Authors:
Schopf, J. William
Publication:
Proceedings of the National Academy of Sciences of the United States of America, Volume 91, Issue 15, pp. 6735-6742
Publication Date:
07/1994
Origin:
JSTOR
DOI:
10.1073/pnas.91.15.6735
Bibliographic Code:
1994PNAS...91.6735S

Abstract

Over the past quarter century, detailed genus- and species-level similarities in cellular morphology between described taxa of Precambrian microfossils and extant cyanobacteria have been noted and regarded as biologically and taxonomically significant by numerous workers world-wide. Such similarities are particularly well documented for members of the Oscillatoriaceae and Chroococcaceae, the two most abundant and widespread Precambrian cyanobacterial families. For species of two additional families, the Entophysalidaceae and Pleurocapsaceae, species-level morphologic similarities are supported by in-depth fossil-modern comparisons of environment, taphonomy, development, and behavior. Morphologically and probably physiologically as well, such cyanobacterial "living fossils" have exhibited an extraordinarily slow (hypobradytelic) rate of evolutionary change, evidently a result of the broad ecologic tolerance characteristic of many members of the group and a striking example of G. G. Simpson's [Simpson, G. G. (1944) Tempo and Mode in Evolution (Columbia Univ. Press, New York)] "rule of the survival of the relatively unspecialized." In both tempo and mode of evolution, much of the Precambrian history of life-that dominated by microscopic cyanobacteria and related prokaryotes-appears to have differed markedly from the more recent Phanerozoic evolution of megascopic, horotelic, adaptationally specialized eukaryotes.
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