Re: REVERSALS etc

["Ken Kinman" <kinman@hotmail.com>]

    I believe that Piciformes is very likely NOT holo(mono)phyletic (i.e. 
paraphyletic at best, but perhaps polphyletic).  Haven't seen evidence that 
Apodiformes has the same problem, but who knows.
    As for TRUE reversals, the only clear candidates would be: Losses of 
genes.  As long as the gene (or genes) for a character are still present, 
there is always the potential of "turned-off" genes getting turned back on.  
But once the reversal of "gene loss" occurs, the probability of ever getting 
the same gene back are astronomically remote (unless you are one of those 
genetically "promiscuous" prokaryotes, and even then it's extremely 
improbable).
    Other than gene loss, "reversals" are a relative term and subject to 
controversies over probabilities.  This is just one of many homoplastic 
(homoplasic, homoplasious) complexities that challenge evolutionary 
systematists.  And it's especially true in paleontology, given the near 
total absence of genetic and other molecular data from fossils (at least 
given our current technology).
          ------ Ken
*****************************************
Darren Naish wrote:

> Philidor11 wrote...
>
> > Can anyone suggest an example of a true reversal?
>
> Mandibular dentition in one genus of marsupial tree frog. More debatably,
> tabular bones in chrysochlorids (golden moles).
>
> Incidentally, I read Chris Brochu's paper on archosaur systematics in the 
> recent
> _Journal of Paleontology_ last night. Excellent review, but, in the bit 
> about
> bird relationships, Chris says that no-one doubts the monophyly of 
> Piciformes
> (woodpeckers, barbets, toucans, honeyguides, jacamars) or Apodiformes
> (swifts, swiftlets and hummingbirds). Though monophyly of these groups is
> currently the consensus view, this is a little surprising: piciform 
> monophyly has
> actually been quite controversial and formed the subject of various
> argumentative papers by Olson, Cracraft and Raikow. Apodiform monophyly
> has also been contested and some authors have separated hummingbirds (as 
> the
> Trochiliformes) from the other apodiforms. Anyway, back to work.


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