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The Origin of Animal Body Plans

Recent fossil finds and new insights into animal development are providing fresh perspectives on the riddle of the explosion of animals during the Early Cambrian

Douglas Erwin, James Valentine, David Jablonski

Figure 1. With its five eyes...Click to Enlarge Image

For its first 3 billion years on earth, life was no larger or more sophisticated than a single cell. All of that changed when almost 600 million years ago new, multicellular life forms appear in the fossil record. Starting with simple soft-bodied creatures this evolutionary innovation culminates in the "Cambrian explosion," a burst of biological creativity unprecedented in earth's history. The Cambrian epoch saw the creation of hundreds of life forms stranger than anything humanly imaginable. Many of these animals are now extinct, but those that remained established all of the basic bodyplans of all animals that evolved since. Until recently, it was difficult to understand the biological mechanisms underlying the creation and evolution of body architectures, much less establish lines of descendence. But new discoveries in molecular biology and development, as well as new ways of analyzing genetic relationships is helping scientists reconstruct the earliest chapters in the history of life on earth.


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