[Taxacom] 53 million year rabbit foot

Kenneth Kinman kennethkinman at webtv.net
Wed Nov 23 21:12:58 CST 2011


Hi Jason,  
       Well, it depends on the particular case.  In some cases, I can
see making the assumption that the stem is "practically" nonexistent.
However, if there is very good evidence that taxon X and taxon Y are
sister taxa, but one has a long stem-lineage containing uncontroversial
fossils and the other does not have such stem fossils, then it seems to
me more parsimonious (conservative?) to assume that the taxon lacking
known stem fossils also has a stem lineage that is just as long, but for
some reason the fossils have not been discovered.      

      The reason could be relatively low population numbers, very
restricted habitat, less fossilizable body parts, or something else.
But I think it would be unwise to assume the stem is nonexistent in such
a case.  Of course, on the other hand, if the evidence that X and Y
actually are sister taxa is not very strong, one could then hypothesize
that one is actually paraphyletic with respect to the other, and the
daughter taxon could thus have such a short stem that lack of fossils
could be because of that.  It all depends on the particular case, which
assumptions I would make.     
               ---------Ken   

------------------------------------------------------
Jason wrote:            
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!. Best Jason 






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