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Re: Archaeopteryx



George Olshevsky (Dinogeorge@aol.com) wrote:

...

  Though Mike Keesey wrote of vertebral frame shift in humans, the same is
known for giraffes. Observations on variable condensation and development
of the alular digit in kiwis and absence of a condensation of the third
digit from the third digit bud in embryos is known (1), and using
inhibitors, the same is known in alligator embryos (2). Finally, Wagner
and Gauthier (3) has satisfied case study for "frameshift" and it is not a
cladist trick. My understanding is also that frogs have recently been
found to exhibit digit frame shift, but not sure this has been published.

1] Parker, 1891 (Philosophical Transactions of the Toyal Society of London
   181: 25-134)

2] Müller, 1994 (in Weiser [ed.] die Evolution der Evolutionstheorie:
   155-193)

3] From Wagner & Gauthier, 1999 (Proceedings of the National Academy of
   Sciences, Philadelphia 96: 5111-5116):

"A similar shift in digit identity with condensation loss is evident in
the hand of the vestigial wing in the Kiwi [Apteryx (55)]. Kiwis have only
two fingers, and, in the absence (or near absence) of digit DI (CII),
digit DII (CIII) sometimes can display the number and shape of phalanges
natural to digit DI instead of digit DII or a combination of attributes of
both fingers (Fig. 5b and c). It is equally revealing that, in Kiwis, the
third condensation (CIII) never gives rise to a third digit (DIII).
Natural variation of this sort demonstrates unambiguously that there is no
one-to-one relationship between digit identity (D) and condensation
identity (C). That is to say, depending on the theropod in question,
morphological features characteristic of a thumb (DI) can develop from any
of three different condensations, that is, either CI (e.g.,
Herrerasaurus), CII (e.g.,Archaeopteryx), or CIII (e.g., some Apteryx)."
[pg. 5114-5115]

  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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