Early Animal Evolution: Emerging Views from Comparative Biology and Geology
Abstract
The Cambrian appearance of fossils representing diverse phyla has long inspired hypotheses about possible genetic or environmental catalysts of early animal evolution. Only recently, however, have data begun to emerge that can resolve the sequence of genetic and morphological innovations, environmental events, and ecological interactions that collectively shaped Cambrian evolution. Assembly of the modern genetic tool kit for development and the initial divergence of major animal clades occurred during the Proterozoic Eon. Crown group morphologies diversified in the Cambrian through changes in the genetic regulatory networks that organize animal ontogeny. Cambrian radiation may have been triggered by environmental perturbation near the Proterozoic-Cambrian boundary and subsequently amplified by ecological interactions within reorganized ecosystems.
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We thank M. A. Fedonkin, S. Xiao, and J. P. Grotzinger for permission to photograph some of the specimens in Fig. 1; J. Grenier, L. Olds, and S. Paddock for help with illustrations; H. Bode, E. Davidson, K. Peterson, and G. Budd for pointers; S. Bengtson, N. Shubin, A. Adoutte, E. Davidson, J. Grenier, and G. Halder for comments on the manuscript; and J. Wilson for help with its preparation. A.H.K. is supported in part by the NASA Astrobiology Institute. S.B.C. is an investigator of the Howard Hughes Medical Institute.
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Volume 284 | Issue 5423
25 June 1999
25 June 1999
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