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

Re: Archie skull pneumatics?



David Marjanovic (david.marjanovic@gmx.at) wrote:

<Even though generations of paleontologists have assumed they knew what it
looked like in *Archaeopteryx*. Well, the postorbital is there, the
postorbital process on the jugal is there, but whether they met is
unknown.>

  It is these very "generations of paleontologists" that have predicated
the myth that one could actually tell. In most specimens it is not at all
possible to determine the extent of the postorbital bar from _either)
jugal or postorbital bones. In only two specimens is the region well
enough preserved to say anything; in the first, the Fifth or the
Eichstätt, the jugal preserves a tiny splint that does not contact the
postorbital at all; in the second, the Seventh or the Aktien-Verein, *A.
bavarica*, the elements are separated and the postorbital incomplete and
small, not permitting any fit to what is an actually quite short and small
ascending process of the jugal, relative to the size of the orbit. It is
thus not possible to determine a fully closed postorbital bar or even a
partial one, as the complete extent of this region is unknown. The various
restorations of the region result from varying degrees of preservation and
assumptions about how much can be infered from the preserved elements. In
the Fifth, this region is assumed to be a complete bar despite the absence
of any direct evidence, and in the Seventh, unless one posits a unique
super-long jugal ramus of the postorbital, this region is not likely to be
complete.

<Really? -- Now don't tell me you've adopted my old argument that a)
*Nomingia* has 24, so *Caudipteryx* may have had 24, too, and b) either
the last preserved vertebra which is shown in Vertebrata PalAsiatica is a
pygostyle (22 + 23 +  24) or a pygostyle (23 + 24) has fallen off...>

  We can do without the sarcasm. *Caudipteryx* indeed has 24 caudals, or
as much as 26 in one specimen. The idea that there must have been a
pygostyle to result in the loss of several verts in one specimen, is
unnessecary, but this region preserves a distinct caudal ball and it may
in fact pertain to a antoher vertebral articulation. However, this is
pointless. *Caudipteryx* caudal count is not stable, and the original
projection of caudal counts from Ji et al. were off at an estimate. This
is based on my own personal study of the tail regions, and I am entirely
willing to be wrong in the light of better data.

  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)

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com