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.

Phylogenetic analysis and morphometrics have been developed by biologists into rigorous analytic tools for testing hypotheses about the relationships between groups of species. This book applies these tools to paleontological data. The fossil record is our one true chronicle of the history of life, preserving a set of macroevolutionary patterns; thus various hypotheses about evolutionary processes can be tested in the fossil record using phylogentic analysis and morphometrics. The first book of its type, Fossils, Phylogeny, and Form will be useful in evolutionary biology, paleontology, systematics, evolutionary development, theoretical biology, biogeography, and zoology. It will also provide a practical, researcher-friendly gateway into computer-based phylogenetics and morphometrics.

Patterns of evolution, as illustrated by the fossil record

More than two thirds of all living organisms described to date belong to the phylum Arthropoda. But their diversity, as measured in terms of species number, is also accompanied by an amazing disparity in terms of body form, developmental processes, and adaptations to every inhabitable place on Earth, from the deepest marine abysses to the earth surface and the air. The Arthropoda also include one of the most fashionable and extensively studied of all model organisms, the fruit-fly, whose name is not only linked forever to Mendelian and population genetics, but has more recently come back to centre stage as one of the most important and more extensively investigated models in developmental genetics. This approach has completely changed our appreciation of some of the most characteristic traits of arthropods as are the origin and evolution of segments, their regional and individual specialization, and the origin and evolution of the appendages. At approximately the same time as developmental genetics was eventually turning into the major agent in the birth of evolutionary developmental biology (evo-devo), molecular phylogenetics was challenging the traditional views on arthropod phylogeny, including the relationships among the four major groups: insects, crustaceans, myriapods, and chelicerates. In the meantime, palaeontology was revealing an amazing number of extinct forms that on the one side have contributed to a radical revisitation of arthropod phylogeny, but on the other have provided evidence of a previously unexpected disparity of arthropod and arthropod-like forms that often challenge a clear-cut delimitation of the phylum.