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Re: Dinosaur beaks



Krix Kripchak (MariusRomanus@aol.com) wrote:

<How this statement is related to anything I stated previously is lost to
me... It is I that stated that making jumps in conclusion based on what is
preserved and what is not is at best arm chair conjecture.>

  This is untrue. Variable states of preservation are relative to
organisms. Stating that some things are evident in how something
preserves, such as the "robust" architecture of *Confuciusornis*' skull
implying the beak WOULD be preserved, is in itself, arm chair, since the
study of taphonomy doesn't MATTER what kind of animal is involved, or even
the tissues involved; the whole issue of relative preservation, as I tried
to outline in my lizard example and completely cogent in regards to the
rest of my post, yours, and my initial reply, is that there is no reason
why a certain tissue MUST preserve. A very good example of this is how
hair and feathers do not always preserve in mammals and birds from Messel
or Liaoning/Ningcheng deposits, and feathers or wing impressions, or scale
impressions, are not always present in *Archaeopteryx*, pterosaurs, or
crocs from the various Solnhofen levels.

<When it comes to preservation, we see very odd events if we are looking
for a basic standard. Skippy is all guts and pretty much zero integument.
Skippy was not produced by magic but by the local conditions that may not
even have existed just a few feet away. Or, these conditions could have
also been quite common for miles around. Who knows.>

  *Scipionyx* shows that these are stains, and what is not always notable
is that not all of these stains show up on UV, and the slab containing it
is almost a rainbow medley of colors (I've seen the original as well as a
cast slab, and I have discussed this with Marco Signore in the past).
There are very few true impressions in these, including the trachea, but
they do exist. Skin, scale, or "fluff" are not in evidence, but this is
true for various specimens of *Archaeopteryx* (e.g., the fifth or
Eichstätt specimen is "bare"). Mineral replacement of soft-tissue organs
are very, very rare, and the case of Willo's heart is hardly settled, but
both sides have relative expertise in the same thing to contend with;
*Scipionyx* lacks minerally replaced organs, just stains, as in many of
the Chengjiang "craniates."

<As stated before, modern birds have varying forms of prokinesis that
allow the premaxilla to act as a sort of manipulation tool not seen in
basal forms. In parrots, this joint has become a completely diarthrosis
style joint. In basal birds like *Confuciusornis*, this was not the case,
and few signs of the later advanced prokinesis are seen. Trying to draw
correlation's between modern birds and their basal counterparts avoids
huge amounts of selection over millions of years.>

  The corellation exists, however, irrelevant of phylogeny; relative
robusticity of the lachrymal and jugal coexist with bending stresses
depending on bite factors and jaw occlusion, whether or not there is a
maxillo-jugal joint (as in many other prokinetic birds); this correlation
is determinable by examination of finch skulls from house sparrows to
ground finches, which had plucking and fruit eating and insect eation to
nuck cracking diets, as in parrots. Lorries and "true" parrots show the
same correlation, robusticity increases up from lorries through to macaws
depending on the plucking to cracking functions of the jaw. Other
prokinetic nutcracking birds, as in some cardueline finches, show the same
thing (including cardinals) along with the crossbill. 

<But even still, we see an increase in the size of the premaxilla in
*Confuciusornis* as well as the lateral movement of the nasals. This is
closer to what we see in modern birds.>

  This would seem to suggest a mechanical adaptation that, barring the
warning given above: "Trying to draw correlation's between modern birds
and their basal counterparts avoids huge amounts of selection over
millions of years." These features are seen in OTHER Liaonign birds, as
well, most of whom are more advanced, have teeth, large premaxillae, and
lateral and robust lachrymals ALONG with loss of temporal bones. The
adaptations between the two (*Confuciusornis* and parrots) are functional,
relating to diet.

<Since it is the premaxilla that is being claimed here to have had a
rhamphotheca,>

  And the maxilla, and the dentary. I have pictures of some specimens that
show the jaws so ornamented.

<it would be easily derived that this basal bird would have had a much
larger rhomphotheca in general, relative to other basals... Hence, a
higher degree of preservation.>

  How so? Of the hundred or so catalogued *Confuciusornis*, only two or
three are known to heave ANY rhamphotheca. This is not a higher degree at
all. The first rhamphotheca was announced in 1999 from a discovery earlier
that year; *Confuciusornis* has been continuously been recovered over
western Liaoning since 1994, and up to now, only two or three specimens
have this, not knowing how many may be present in private hands, the
institutional recovery is not site-based and just as general as the
private collectors.

<Even though the premaxilla is much larger in this animal, we still find
beak preservation rare, with the amount not preserved being larger by far
than the region hypothesized to be present in animals such as
*Archaeopteryx* and *Microraptor*.>

  Who supports *Microraptor* beaks? This is at odds with known
premaxillary morphology, limited to the holotype in medial view. And fully
toothed. And as for negative evidence, please don't accuse me of using
this: it was my statement in the beginning that states of preservation
cannot be used to attest to their natural, living condition. You really
should read my original post.

  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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