[Taxacom] 53 million year rabbit foot
jfmate at hotmail.com
Wed Nov 23 16:23:59 CST 2011
Hi Ingo and Ken,
sorry for what will be a rather short and uninteresting clarification. I actually meant that without fossils, and for all practical reasons, we can assume that the stem is non-existant if we are being conservative. It is a matter of choice on how many assumptions you can make regarding timing, but this becomes a moot point when you have fossils belonging to the stem and crown. Hence I think we are in general agreement in this regards. That was a fun exchange!.
> From: kennethkinman at webtv.net
> To: taxacom at mailman.nhm.ku.edu
> Date: Tue, 22 Nov 2011 03:56:20 +0000
> Subject: Re: [Taxacom] 53 million year rabbit foot
> Hi Ingo,
> Since Jason said that the stem lineage is real, I'm
> pretty sure he meant to say that it was nonextant (rather than
> Anyway, if a taxon is very rich in extant subtaxa, and
> very poor in fossils, there are often no known fossils in the stems
> (such as bacteria, many worm phyla, various dipteran taxa, etc.).
> Without known fossils, many of their stems are empty sets at the
> present, and many are likely to remain so for the foreseeable future.
> Sometimes the extant taxa were splitting off (radiating) very
> quickly, and the stem age and crown age are virtually the same (meaning
> that stem fossils may never be found, even if they were very rarely
> preserved at all). So in such cases, one could perhaps actually argue
> that the stem lineage is very close to being nonexistent (temporally
> collapsing, as Jason noted).
> Ingo wrote:
> I would agree on the last sentence
> and disagree with the first. I think it is very existant. It is the
> (estimated) time between the split of a certain group from its sister
> clade (stem age) to the first speciation event that led to two extant
> subclades (crown age).
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