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Origin of the Eumetazoa: testing ecological predictions of molecular clocks against the Proterozoic fossil recordMolecular clocks have the potential to shed light on the timing of early metazoan divergences, but differing algorithms and calibration points yield conspicuously discordant results. We argue here that competing molecular clock hypotheses should be testable in the fossil record, on the principle that fundamentally new grades of animal organization will have ecosystem-wide impacts. Using a set of seven nuclear-encoded protein sequences, we demonstrate the paraphyly of Porifera and calculate sponge/eumetazoan and cnidarian/bilaterian divergence times by using both distance [minimum evolution (ME)] and maximum likelihood (ML) molecular clocks; ME brackets the appearance of Eumetazoa between 634 and 604 Ma, whereas ML suggests it was between 867 and 748 Ma. Significantly, the ME, but not the ML, estimate is coincident with a major regime change in the Proterozoic acritarch record, including: (i) disappearance of low-diversity, evolutionarily static, pre-Ediacaran acanthomorphs; (ii) radiation of the high-diversity, short-lived Doushantuo-Pertatataka microbiota; and (iii) an order-of-magnitude increase in evolutionary turnover rate. We interpret this turnover as a consequence of the novel ecological challenges accompanying the evolution of the eumetazoan nervous system and gut. Thus, the more readily preserved microfossil record provides positive evidence for the absence of pre-Ediacaran eumetazoans and strongly supports the veracity, and therefore more general application, of the ME molecular clock.
Document ID
20050218673
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Peterson, Kevin J.
(Dartmouth College Hanover, NH 03755, United States)
Butterfield, Nicholas J.
Date Acquired
August 23, 2013
Publication Date
July 5, 2005
Publication Information
Publication: Proceedings of the National Academy of Sciences of the United States of America
Volume: 102
Issue: 27
ISSN: 0027-8424
Subject Category
Geosciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Evolutionary Biology
Non-NASA Center

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