Re: Fossil calibration

From: bivalve <>
Date: Wed Apr 07 2004 - 15:21:16 EDT

>I was wondering about how to get at reliable newer dates. Of course, the reliability of papers dedicated to dating particular fossils usually can be assessed reasonably well. But how about molecular phylogenies etc.?<
>I was struck by the fact that the papers most criticized by Graur and Martin were published in such respectable journals as Nature and Science, and Bromham et al. published their range-less dates (without any literature references!) in the equally respectable PNAS: 95 (1998), 12386. How reliable are the peer review processes of these leading journals? <

I don’t know of anything as exhaustive as the Fossil Record volumes, but several references exist for individual groups. For example, there are newer Treatise on Invertebrate Paleontology volumes for several phyla.

Nature, Science, PNAS, etc. seem rather enthusiastic about molecular biology, which tends to be much stronger on molecular than on biology. Thus, the review probably emphasized molecules rather than paleontology or statistics. I suspect that the situation is worse for molecular biology journals. The problem is not confined to this field-in general, beware of claims outside the area of expertise of the authors.

There are molecular clock studies that use more realistic models than a linear clock, as well as studies that have plausible error bars (very wide). Additional problems for clock models have recently been identified. For example, in an interval of evolutionary radiation, a larger proportion of the genetic variability will be preserved in various lineages than during ordinary background evolution. This will make the molecular clock dates for radiation events look too old. Redating evolutionary radiations has been a popular application of molecular clocks. Changes in environmental mutagens (radiation, ozone, etc.) become significant over very long time intervals.

As an example, the 18S gene, with about 1800 bases, shows no difference between Eucrassatella and Astarte, despite a divergence at least in the Cretaceous, whereas species of Tridacna that diverged within the Cenozoic show very large differences (including a lot of extra bases).

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL 35487-0345 USA

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa

Received on Wed Apr 7 15:21:50 2004

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