[Taxacom] Paraphyletic tagging

[Kenneth Kinman]

Hi Curtis,          Well, we've not created a taxon based "only" on what it lacks.  It must also possess the amniote synapomorphy. Otherwise it would also include non-amniotes.  It's sort of like a medical diagnosis done on a dual basis---not only on possession of certain symptoms, but also on the lack of other symptoms.        As for the mammalian synapomorphy, I don't think it happened in a single speciation event, but it probably wasn't "gradual" either.  In terms of the punctuated-equilibrium theory, I would say that it happened during a punctuation rather than a period of gradual equilibrium.  It could take a hundred generations and still be relatively sudden on a geological time scale.  In any case, ear bones make a better synapomorphy than mammary glands or hair.              -----------------Ken
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> Date: Fri, 3 Oct 2014 12:39:01 -0700
> From: lists at curtisclark.org
> To: taxacom at mailman.nhm.ku.edu
> Subject: Re: [Taxacom] Paraphyletic tagging
> 
> To be clear, although Stephen's answer works for the extant species, Ken 
> guessed that I meant more globally.
> 
> On 2014-10-03 7:22 AM, Kenneth Kinman wrote:
> >
> >        I would rather phrase it: "Amniotes lacking the synapomorphies 
> > of Mammalia and Aves".
> 
> So we've created a taxon based on a lack?
> 
> > Hair and feathers would not be the best synapomorphies to pick as they 
> > evolved too gradually (even baby Tyrannosaurus rex may have had 
> > feathers).
> 
> And there are even hairy things in some Ornithischia that have been 
> interpreted as being homologous with feathers. I'm not saying that 
> thecodonts had feathers, but if a thecodont fossil with clear feathers 
> was discovered, I wouldn't be astounded.
> 
> > For Mammalia, the best synapomorphy so far discovered seems to be when 
> > the three ear bones decoupled from the mandible.
> 
> But unless that happened in a single speciation event, there is still 
> the issue of where in a gradual shift do we draw the line.
> 
> -- 
> Curtis Clark        http://www.csupomona.edu/~jcclark
> Biological Sciences                   +1 909 869 4140
> Cal Poly Pomona, Pomona CA 91768
> 
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