[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

re: bat/ptero wings

David Peters (davidrpeters@earthlink.net) wrote:

<On a similar note, Unwin, Frey, Martill, Clarke and Riess (1996)
attempted to figure out what the heck a pteroid was in pterosaurs. They
discovered that it was indeed a bone, but they could never figure out
which one. Of course they ignored the possibility of pterosaurs being
protorosaurian in descent. Had they done so, they would have trumped my
2002 paper that identified the homology of the preaxial carpal and pteroid
as migrating centralia.>

  The os centrale is usually inside the wrist, part of the second level of
carpals. It's emmigration external to the mobile wrist structure and loss
of the rest of the middle carpals has not been demonstrated, even by
Peters, rather than a "just-so" story to explain possible
pterosaur-"protorosaur" homologies. No one has considered either of two
possibilities, to my knowledge: 1) the pteroid represents a modified
tendon, as in the flexor bone found in various talpids and chrysochlorids,
which features as ossification of the flexor tendon of the wrist, or 2)
that this represents a possible homology to one of the digits. If birds
can undergo a frameshift, as has been theorized, so may too had pterosaurs
simply translated identity from the pollex onto the second finger. Thus,
the digits would be pteroid-II-III-IV-V, not I-II-III-IV-X. These are
balanced, I think, hypotheses. Other theories include possible modified

<Ahhh, but we do have the Archaeopteryx for pterosaurs. And both of the
taxa you mention are the best candidates known to date. There has never
been a cladistic analysis that knocks either out of the ring. And if you
don't like these two, you can fall back to Cosesaurus and even
Langobardisaurus. Any of these four will beat anything offered up by the
archosaur guys.>

  Neither taxa mentioned have a complete hand/arm, and *Sharovipteryx*
would imply the reverse of the "missing link" scenario, favoring the leg
in neglect of the arm, as one would say. Others continue to fail to find
the tracings convincing, even when seen under detailed examination by
microscop, rather than Photoshopped interpretations. Not to say they are
wrong, but they have yet to be corroborated by _one_ independant study.

<But, that being said, I'd love to see a competing analysis. In four years
no one has even tried. Somehow it stopped being a "hot topic".  I wonder

  Because they've been working on it? Not so eager to publish. This is why
some theropod phylogenies take so long to work themselves into press,
especially when they are very, very large. It was 4 years between the
publication of Holtz' _GAIA_ and _the Dinosauria, 2nd Ed._ phylogenies,
with only a little elaboration between them. Intervening publication of
Rauhut's phylogeny in 2002, etc., account for work being done by separate
groups on the whole of Theropoda, with the only other one being done by
Sereno in 1999 (and even then, it was a "split" analysis with only
sections of clades being represented at once, a technique that reduces
some problems such as long-branch attraction.

  Similarly, one cannot criticize or even compare analytical work that is
not available. Many statements are made in reference to an analysis that
no one can judge or reference, or otherwise test. If these results cannot
be made available when they are discussed, it may be wise to limit
reference to them until they ARE available.


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)

Do you Yahoo!? 
All your favorites on one personal page ? Try My Yahoo!