Origin and Early Evolution of the Metazoa Questions: Our research is aimed at documenting the early history of metazoans (multicelled animals) using both the fossil record and also the historical information contained within the genomes of living organisms. We are interested in the relationships among animal phyla, the nature of early ecosystems, and the extent to which early experimentation (display of body plans) has been decimated by extinction. Procedures: We use paleontological data (rock samples, fossil speciments, field and laboratory measurements etc.) from 500-600 million-year-old sites in Africa, Asia, Australia, Europe and North America to reconstruct extinct groups of early metazoans and related multicellular organisms. Similar data are used to analyze the paleoecology, taphonomy, and paleoenvironmental setting of the fossiliferous deposits. Computer-based images and models are used to make reconstructions and interpretations of the paleobiology of extinct organisms. A parallel program involves sequencing genes from appropriate living organisms so that so that the position of critical higher taxa within the metazoan tree may be determined. We are currently sequencing the 18S rRNA genes of two kinds of aplacophoran molluscs collected from the north coast of Papua New Guines and the continental shelf of Southern California. Results: Our work has shown that multicellular organisms have an extensive Precambrian history that began prior to 2 billion years ago. Animals diversified prior to about 600 million years ago, perhaps in response to major environmental changes which occured on Earth at that time.