A study, published today (Mar. 16) in the online early edition of the Proceedings of the National Academy of Sciences (PNAS), analyzed molecular dating material collected from land plants, including 33 fossil calibrations, to reach its conclusion. That conclusions is that the origin of crown-clade angiosperms took place during the late Triassic period, which is “considerably older than the unequivocal fossil record of flowering plants or than the molecular dates presented in recent studies”.
According to the abstract, the study permitted “rates of molecular evolution to be uncorrelated across the tree, and take into account uncertainties in phylogenetic relationships and the fossil record”. The authors go on to state that they “attached a prior probability to each fossil-based minimum age, and explored the effects of relying on the first appearance of tricolpate pollen grains as a lower bound for the age of eudicots”.
The authors also state that “many of our divergence-time estimates for major clades coincide well with both the known fossil record and with previous estimates”.
Finally, the authors state that “although the methods used here do help to correct for lineage-specific heterogeneity in rates of molecular evolution (associated, for example, with evolutionary shifts in life history), we remain concerned that some such effects (e.g., the early radiation of herbaceous clades within angiosperms) may still be biasing our inferences”.
The study was conducted by Stephen A. Smith of the National Evolutionary Synthesis Center in Durham, NC, U.S.A., and Jeremy M. Beaulieu and Michael J. Donoghue of the Department of Ecology and Evolutionary Biology at Yale University, New Haven, CT, U.S.A. Donoghue is also associated with the National Evolutionary Synthesis Center.
For the complete journal article see the following URL:
http://www.pnas.org/content/early/recent.
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