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Re: Land Plants Origins Pushed Back




James,
I'm not sure exactly what you mean by "timeline", but clearly if Precambrian fossils of land plants were found, timelines would have to be changed to show them originating much earlier. But perhaps you are speaking of the actual subdivisions of geological time.
As far as changing the actual framework of Late Precambrian (Neoproterozoic) subdivisions and their ages (which is still rather fluid and inexact), I assume those will continue to be based more on the Metazoan fossil record, just as is the case with Paleozoic, Mesozoic and Cenozoic subdivisions.
But with the increasing evidence that many major faunal changes (mass extinctions) correspond with major impact events, it wouldn't surprise me if geological evidence for such massive impacts eventually became the basis for a more precise subdivision of the Late Precambrian. However, since we are still arguing over the importance of Mesozoic impacts, I doubt that we will be seriously debating Precambrian subdivisions on that basis anytime soon, but I'm not a geologist so I may be underestimating the progress that may have been made on that subject. So much going on and so little time to keep up with the explosion in scientific knowledge.
---Cheers, Ken
*******************************************


From: JAMES ARONIS <Apollo@MLink.net>
Reply-To: Apollo@MLink.net
To: Dinosaur Mailing List <dinosaur@usc.edu>
Subject: Re: Land Plants Origins Pushed Back
Date: Wed, 15 Aug 2001 12:15:17 -0400

If indeed this molecular 'evidence' is paralleled with the discovery of new fossil
records, will that necessitate changes made to the geologic timeline in order to
reflect these new discoveries?


Ken Kinman wrote:

> Eric,
> Some molecular "clocks" are better than others, and the possiblility of
> skewing should be considered.
> However, even if the dates are too early, it clearly points out the
> probability that there were primitive bryophytes (liverworts and possibly
> even mosses), fungi, and lichens on land during the Precambrian. The
> question is if there is any trace of them in the fossil record, and if we
> look hard enough, I bet someone will find such traces eventually. The
> fossil record is notoriously incomplete, especially when it comes to
> soft-bodied organisms.
> -------Ken
> P.S. I should make it clear that I do not buy Retallack's hypothesis that
> vendobionts were lichens. However, there are some controversial Cambrian
> fossils of "fungi" that should perhaps be carefully reexamined in light of
> these new findings.
> ******************************************
> >From: ELurio@aol.com
> >Reply-To: ELurio@aol.com
> >To: rtravsky@uwyo.edu, dinosaur@usc.edu
> >Subject: Re: Land Plants Origins Pushed Back
> >Date: Wed, 15 Aug 2001 09:11:55 EDT
> >
> >Here we go AGAIN!!!! There's ample evidence that rapid evolution can
> >squewer
> >the molecular clock bigtime. When the fossil record and the molecular
> >"record" disagree on chronology, always go with the fossil record.
> >
> >eric l.
>
> _________________________________________________________________
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