Douglas Erwin is a paleobiologist with interests in evolutionary innovations and the end-Permian mass extinction and subsequent biotic recovery, among other areas. Recent field projects have taken him to China, South Africa, and Canada. He is Senior Scientist and Curator in the Department of Paleobiology at the National Museum of Natural History and a professor at the Santa Fe Institute. He is the author of six books, including most recently Extinction: How Life on Earth Nearly Ended 250 Million Years Ago (Princeton University Press, 2005).

Jim Valentine has spent the last 50 years trying to understand the paleoecological and macroevolutionary principles that have shaped the fossil record of the marine biosphere. He has found the earliest animal records to be a particular challenge to such interpretation and a delight to investigate. He is active Professor Emeritus of Integrative Biology at the University of California, Berkeley, and the author of many books, including most recently On the Origin of Phyla (University of Chicago Press, 2004).

The Cambrian Period records one of the most extraordinary transitions in the history of life. Although animals may have first appeared nearly 700 million years ago, with the earliest sponges, their initial diversifications appear to have been modest until a richly diverse fossil fauna appeared abruptly about 170 million years later. In The Cambrian Explosion, Erwin and Valentine synthesize research from many fields to explain why there was such remarkable novelty of animal forms.