The origin of animals: Can molecular clocks and the fossil record be reconciled?

• Published in: BioEssays Vol. 39; no. 1; pp. 1 - 12
• Main Authors: Cunningham, John A., Liu, Alexander G., Bengtson, Stefan, Donoghue, Philip C. J.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-01-2017
• Subjects: Anatomy; Animals; Biological Evolution; Cambrian explosion; Clocks; Ecosystems and species history; Ediacaran; Ekosystem och arthistoria; Fossils; Inspection; Metazoa; molecular clocks; Neoproterozoic; Phylogeny; Preservation; Time; trace fossils; ediacaran; Cambrian explosion; trace fossils; molecular clocks; neoproterozoic; metazoa
• ISSN: 0265-9247; 1521-1878; 1521-1878
• DOI: 10.1002/bies.201600120

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.
Molecular clocks estimate that animals originated over 100 million years before the first definitive metazoan fossil evidence in the Cambrian. However, these records are less divergent than is often claimed: modern clock analyses do not predict Neoproterozoic crown‐representatives of animal phyla, and some Neoproterozoic fossils are reasonably interpreted as metazoans.