title: The origin of animals: Can molecular clocks and the fossil record be reconciled?
abstract: The evolutionary emergence of animals is one of the most significant episodes in the history of life, but its timing remains poorly constrained. Molecular clocks estimate that animals originated and began diversifying over 100 million years before the first definitive metazoan fossil evidence in the Cambrian. However, closer inspection reveals that clock estimates and the fossil record are less divergent than is often claimed. Modern clock analyses do not predict the presence of the crown-representatives of most animal phyla in the Neoproterozoic. Furthermore, despite challenges provided by incomplete preservation, a paucity of phylogenetically informative characters, and uncertain expectations of the anatomy of early animals, a number of Neoproterozoic fossils can reasonably be interpreted as metazoans. A considerable discrepancy remains, but much of this can be explained by the limited preservation potential of early metazoans and the difficulties associated with their identification in the fossil record. Critical assessment of both records may permit better resolution of the tempo and mode of early animal evolution.
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol, UK.|Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm, Sweden.
authors.forename: John A
authors.initials: JA
authors.lastname: Cunningham
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol, UK.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Liu
authors.affiliation: Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bengtson
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol, UK.
authors.forename: Philip C J
authors.initials: PC
authors.lastname: Donoghue
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005580:Fossils; D010802:Phylogeny; D013995:Time
keywords: Cambrian explosion; ediacaran; metazoa; molecular clocks; neoproterozoic; trace fossils