Origin of the Metazoan Phyla: Molecular Clocks Confirm Paleontological Estimates

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 95; no. 2; pp. 606 - 611
• Main Authors: Ayala, Francisco Jose, Rzhetsky, Andrey, Ayala, Francisco J.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 20.01.1998; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Animals; Arithmetic mean; Biological Sciences; Cytochromes; Echinodermata; Echinoderms; Evolution; Evolution, Molecular; Evolutionary genetics; Fossils; Genetic loci; Invertebrates; Marine; Metazoa; Molecular biology; Mollusca; Paleontology; Phylogeny; Proteins - genetics; Taxa; Vertebrates
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.95.2.606

The time of origin of the animal phyla is controversial. Abundant fossils from the major animal phyla are found in the Cambrian, starting 544 million years ago. Many paleontologists hold that these phyla originated in the late Neoproterozoic, during the 160 million years preceding the Cambrian fossil explosion. We have analyzed 18 protein-coding gene loci and estimated that protostomes (arthropods, annelids, and mollusks) diverged from deuterostomes (echinoderms and chordates) about 670 million years ago, and chordates from echinoderms about 600 million years ago. Both estimates are consistent with paleontological estimates. A published analysis of seven gene loci that concludes that the corresponding divergence times are 1,200 and 1,000 million years ago is shown to be flawed because it extrapolates from slow-evolving vertebrate rates to faster-evolving invertebrate rates, as well as in other ways.