Re: PhyloCode Discussion: Crowns, Panstems, and their Correspondence to each oth

["Jaime A. Headden" <qilongia@yahoo.com>]

Tim Williams (twilliams_alpha@hotmail.com) wrote:

<This is something I hadn't considered before. Sadly, many groups at the
level of "family" and "order" have become extinct in last few hundred
years: e.g., birds (Dinornithidae, Aepyornithidae, Raphidae [probably
nested within Columbidae]) and mammals (Thylacinidae, Nesophontidae). 
Under the above definition, these would no longer be considered "crown
groups".>

  Yes.

  I was going to mention this in recent discussions of discussion use of
pan-stems with Marjanovic: crown Mammalia only corresponds to the clade
including monotremes, marsupials, and placentals, and only them and any
descendant of that first ancestor of those three clades. Meaning,
"symmetrodonts" and zhangheotherids are _NOT_ crown mammals. Also, since
pan-stems are applied to _crowns_, Hesperornithes cannot become a
pan-stem.

  However, birds such as moa and elephant birds and dodos still belong to
the crown ratites or columbiforms/columbids, so this is not really that
much of a problem. It only means their smaller population cannot be a
crown. In this same sense, the extinct sandcoliids within Coliiformes do
not get to be crowns, but are still part of one.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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