ORIGIN OF THE METAZOAN PHYLA - MOLECULAR CLOCKS CONFIRM PALEONTOLOGICAL ESTIMATES

The time of origin of the animal phyla is controversial, Abundant foss ils from the major animal phyla are found in the Cambrian, starting 54 4 million years ago. Many paleontologists hold that these phyla origin ated in the late Neoproterozoic, during the 160 million years precedin g the Cambrian fossil explosion. We have analyzed 18 protein-coding ge ne loci and estimated that protostomes (arthropods, annelids, and moll usks) diverged from deuterostomes (echinoderms and chordates) about 67 0 million years ago, and chordates from echinoderms about 600 million years ago. Both estimates are consistent with paleontological estimate s. A published analysis of seven gene loci that concludes that the cor responding divergence times are 1,200 and 1,000 million years ago is s hown to be flawed because it extrapolates from slow-evolving vertebrat e rates to faster-evolving invertebrate rates, as well as in other way s.