[Taxacom] Angiosperm origins: Darwin's "abominable" mystery

[John Grehan]

Molecular clocks are no more valid when they agree with other evidence
than when they do not. My principle objection is the often deliberate
misrepresentation of molecular clocks estimates as actual or maximal
divergence dates (whether or not given as a range). In this case the
minimal estimate provided for the angiosperms is not incongruent with
the biogeographic and morphogenetic evidence. This does not make
Croizat's model any more or less 'correct' than it was in the first
place. But of course for the molecular theorists who regard their
prediction as correct are in effect showing that Croizat was correct as
well.

I am not presenting Croizat as the only theorist to predict the early
origin as others such as Axelrod also mentioned on the list had a
similar idea, although Croizat argued for a mangrove rather than upland
origin.

John Grehan

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Curtis Clark
Sent: Friday, March 19, 2010 9:25 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Angiosperm origins: Darwin's "abominable" mystery

On 3/18/2010 8:28 PM, Kenneth Kinman wrote:
>         However, new molecular evidence published in Proceedings of 
> the National Academy of Sciences earlier this week indicates that even

> the crown clade of angiosperms may have originated as early as the 
> Upper Triassic.

This has long been a bone of contention independent of Croizat. Dan
Axelrod introduced me to the idea of Triassic angiosperms; his
contention was that, because they evolved in the uplands, we'd be
unlikely to see fossils. There were even some fossil contenders, such as
Sanmiguelia (?); I remember that many if not all turned out to not be
angiosperms on closer study.

I think it's interesting that John is okay with molecular clocks when
they agree with Croizat.

-- 
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Director, I&IT Web Development                   +1 909 979 6371
University Web Coordinator, Cal Poly Pomona

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