Re: E and P of Pteros - Notes 1

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

Dave Peters (davidrpeters@earthlink.net) wrote:

<<I'd like to see someone character code a number of the putative juvenile
specimens and see where they pop > up on the cladogram, rather than
prejudicially ignoring their potential contribution due to their apparent 
immaturity. Remember, there are bee-sized bats and birds in this world. It
is an apriori assumption not to consider the wee ones. At worst we could
find that they lump in with some putative adult. At best we might find a
clade of micro-pteros.>>

  I disagree with the issue of why excluding "baby" pterosaurs is wrong as
presented above, because it would be an _a priori_ argument to _include_
them in the analysis, though a potential test of this has been done for
some birds, though also assuming the juvenile nature of the birds is at
fault for lumping (see below) of taxa together. The best determinant for
immaturity are universal criteria of epipophyseal ossification, fusion of
elements, bone grain texture, and comparative relative size of key
cranial/postcranial ratios, though this is changed in some species for
which paedomorphosis is rampant. Overlarge heads is an apparently
paedomorphic condition that may account for the "adult" state in
"anurognathids" and may not actually be a diagnostic "family" trait with
which to group them, if paedomorphosis results in the trend of hominids to
increasingly large heads. Cats look more like big-cat cubs than adults,
and the same is true of dwarf elephants/mammoths. These "juvenile"
qualities are as easily adult features of micro species, and that, too,
must be considered before attempting to define specimens as baby species,
even if they form unique trends that are universal among supposed and
assumed species complexes (aka, because you assume specimen "A" belongs to
species A, does not mean that you can regress species B to look like
specimen "A" to prove that specimen "B" belongs to species B, and so
forth).

Mickey Mortimer (Mickey_Mortimer111@msn.com) wrote:

<Is the latter possibility really "best"?  I know from my coelurosaur
analysis, juvenile enantiornithines (Liaoxiornis, Eoenantiornis, Chiappe's
two SVP 2002 specimens) clump together.  And I don't see why fooling PAUP
into analyzing character distributions under the assumption an oddly
chimaeric clade of taxa exists is useful, or beneficial.>

  I personally think juvenile specimens are the best means by which to
untie the tangled knot of various "bushy" species complexes, but assuming
a specimen belogns to a certain species (see above) can be tricky, since
we don't know what the adult of that species may actually be, and any
growth series is, unless with extraordinary preservation and assumption of
a monochthonous assemblage, we can define age-classes with any margin of
certainty. Most (if not all) pterosaur or bird specimens assumed or
"known" to be juvenile are isolated, and this makes assuming they may
belong to any certain adult relatively untestable, in my opinion. For
example, of all *Confuciusornis* known, not ONE fledgling or chick is
known. And there are literally HUNDREDS of *C.* known. How would we
identify one? Would we assume that it had teeth, so a toothed baby would
be a *C.* or non-*C.* chick, or would it have to be edentulous? Same
scenario, but what if the tail was elongate, multiply-partitioned, and
showed no sign of a pygostyle? Can we truly assume that was a basal
condition during ontogeny to a pygostyle for that species, thereby
"knowing" or "inferring" the adult must have a pygostyle?

=====
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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