The Cambrian Explosion: failed experiments or evolution’s big-bang?

Charles Marshall (Curator in Dept of Invertebrate Paleontology, Museum of Comparative Zoology, Harvard University) is giving a talk on the Cambrian Explosion.

DATE: Friday, 11 Jan 2008
TIME: 4 pm
VENUE: DBS Conference Rm
HOST: Dr David Lohman

The Cambrian “explosion” is a unique episode (~543 to 515 million years ago) in Earth history, when essentially all the animal phyla first appear in the marine fossil record. A variety of environmental, developmental (gentic), and ecological explanations for this complex event have been suggested. Here I develop a new explanation, whereby the unique burst of morphological innovation is best understood as the result of the interplay of the combinatorial bilaterian developmental system and the increase in the number of needs the first bilaterians had to meet as complex ecological interactions developed. The timing of the Cambrian “explosion” was constrained by the evolution of the environment, whereas its duration appears to have been controlled primarily by rates of developmental innovation. The uniqueness of the event is either due to ensuring developmental limitation (canalization), or in my view, most likely represents the exhaustion of ecologically viable morphologies that could be produced by the nascent bilaterian developmental system. This view implies that the morphologies we see in the Cambrian explosion do not represent failed experiments in the history of life. Furthermore, it suggests that the long-term history of life has a much more predictable aspect to it than is typically thought.

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