Re: Protoavis?

[Jeffrey Martz <martz@holly.ColoState.EDU>]

> >I don't think that he does, or at least not a
> >maniraptorian; someone with the article handy might check on that.    
>         That would be good. I'm sure Dr. Currie would rather not be
> mis-paraphrased. :)

     From:

Currie, P.J., and X-J Zhao, 1993.  A new troodontid (Dinosauria,
      Theropoda) braincase from the Dinosaur Park Formation (Campanian) of
      Alberta.  Canadian Journal of Earth Sciences, 30:2231-2247

     Don't even ask me to explain the technical details of this paper, but
in addition to scattering references to _Protoavis_ throughout, Currie
and Zhao include a section in the DISCUSSION devoted to
comparing the bird-like characters of _Troodon_ and _Protoavis_.  They
make a number of corrections involving both Chatterjee's and Currie's own
misinterpretations of parts of Troodon cranial anatomy before the
particular braincase being describing was found.  At least a couple of the
corrections (the anterior tympanic recess, and the relatively kinetic
quadrate-squamosal contact) make _Troodon_ more bird-like
then Chatterjee made out in his _Protoavis_ paper, but overall these
particular corrections seem to have little bearing on the avian features
of _Protoavis_.  
     Currie and Zhao do not explicitly state whether or not they
consider _Protoavis_ to be a theropod, but one of thier opening statements
are highly suggestive: "Although _Protoavis_ has characters suggesting
avian affinities, most of these are also found IN THEROPODS [boldface
mine], which considerably weakens the claim that it is a bird." (p.2243)
     They later go on to say "Comparison between the braincases of
_Troodon_ and _Protoavis_ does suggest that they are amazingly similar for
animals seperated by 160 Ma."  They mention strong similarities between
the brains; both have pretty big brains, an enlarged cerebellum that
shifted the optic lobes ventrolaterally, and also has a large floccular
lobe.  The inner ear is also pretty similar and bird-like in both: "both
have marked differentiation of the canalicular systems and the cochlear
process.  The vestibular region is relatively small and located in a
ventral position to most of the anterior and posterior semicircular
canals.  The anterior semicircular canal is significantly longer then the 
others.  The cochlear process is a relatively long, vertically oriented
tube"(p.2244) , but also... "_Protoavis_ seems to be less bird-like then
_Troodon_ in having only a single exit for the trigeminal."(p.2244) 
      There is a pretty extensive list of other (presumably bird-like)
similarities between _Troodon_ and _Protoavis_, and the authors finish the
section off with: "The braincase of _Protoavis_ is remarkably like that of
a troodontid, and in our opinion has a few unique avian characters.  The
latter would include the streptostylic quadrate and reduction in size of
the olfactory lopes, but the characters are not robust enough to identify
_Protoavis_ as a bird."  Draw your own conclusions, but there it is.
      As far as _Unenlagia_ being more readily accepted then _Protoavis_
in spite of its arguably more fragmentary condition, I don't consider this
to be as unreasonable as you make out.  With the dinosaur-bird connection
already very well established by many decent theropod specimens, another
theropod with additional _Archaeopteryx_ like features is not as
incongruous to the overall apparant pattern of bird evolution as
_Protoavis_.  
      This statement might seem to fit the concept of dogma
bound paleontology pretty well (excluding imporatnt information to fit
the accepted pattern), so I'll give a (bad) analogy.  Lets say
someone found a scrappy Spanish fragment in the West Indies tentatively
dating to about 1492, and an equally scrappy English artifact in Virginia
tentatively dated to 1492.  If you new that ONLY ONE could be correct,
would it be entirely irrational to lend more credence to the date assigned
to the Spanish artifact in light of all the other information availible?
I know the issue has nothing to do with dating, but thats the best I could
think of.  

LN Jeff
O-