Tackling one of the most difficult and delicate of the evolutionary questions, this challenging book summarizes the more recent results in phylogenetics and developmental biology that address the evolution of key innovations in metazoans. Divided into three sections, the first considers the phylogenetic issues involving this area of the tree of life and the elucidation of those relationships that continue to trouble taxonomists. The second section considers the developmental biology of metazoan evolution including the development of the nervous system, sensory organs, and physiological maturation. Part three focuses on the evolution of pattern and process in the Metazoa.

Introduction: A Phylogenomic Journey Through the Animal Tree of Life: Key Innovations in the Evolution of Metazoa; B. Schierwater and R. DeSalle

Tangled Roots in the Animal Tree of Life

Putting Animals in their Place Within a Context of Eukaryotic Innovations; D. Vazquez, L. Wegener Parfrey and L.A. Katz

Elucidating Animal Phylogeny: Advances in Knowledge and Forthcoming Challenges; K.M. Kocot, J.T. Cannon and K.M. Halanych

Key Transitions in Animal Evolution: a Mitochondrial DNA Perspective; D.V. Lavrov

Pending Issues in Development and Phylogeny of Arthropods; J.S. Deutsch

The Earliest Animals: From Genes to Transitions

The Pre-nervous System and Beyond—Poriferan Milestones in the Early Evolution of the Metazoan Nervous System; M. Nickel

A Key Innovation in Evolution, the Emergence of Neurogenesis: Cellular and Molecular Cues from Cnidarian Nervous Systems; B. Galliot, M. Quiquand, M. Miljkovic-Licina and S. Chera

From Cnidaria to "Higher Metazoa" in One Step; F. Boero and S. Piraino

Basal Metazoan Sensory Evolution; D.K. Jacobs, D.A. Gold, N. Nakanishi, D. Yuan, A. Camara, S.A. Nichols and V. Hartenstein

Cnidarian Gene Expression Patterns and the Origins of Bilaterality—Are Cnidarians Reading the Same Game Plan as "Higher" Animals?; E.E. Ball, D.M. de Jong, B. Schierwater, C. Shinzato, D.C. Hayward and D.J. Miller

Key Transitions During Animal Phototransduction Evolution: Co-duplication as a Null Hypothesis for the Evolutionary Origins of Novel Traits; T.H. Oakley and D.C. Plachetzki

Vertebrate Hox Genes and Specializations in Mammals; C. Kappen

Pattern and Process at the Base of the Metazoan Tree of Life

Field Biology of Placozoans (Trichoplax): Distribution, Diversity, Biotic Interactions; V. Buchsbaum Pearse and O. Voigt

Trichoplax and Placozoa: One of the Crucial Keys to Understanding Metazoan Evolution; B. Schierwater et al.

A Food’s-Eye View of Animal Transitions; N.W. Blackstone

Lost in Transition: The Biogeochemical Context of Animal Origins; E. Gaidos

Redefining Stem Cells and Assembling Germ Plasm: Key Transitions in the Evolution of the Germ Line; J. Srouji and C. Extavour

Questions and Discussion