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Re: Archie skull pneumatics?



Rutger Jansma (fam.jansma@worldonline.nl) wrote:

<Guess you're wrong about this one, since teeth _are_ preserved on the
lower jaw of Scansoriopteryx. Just two are preserved, but they are,
despite their low number, nonetheless teeth. Many thanks to HP Aspidel who
found this out and told it to me, so the credit should go to him
actually... The teeth are seen in the counterslab (?) of the specimen of
the skull area that is seperately illustrated. Just enlarge the image to a
degree that it's big but that everything is still visible and look
somewhere below the lacrymal. Here you will find a detached tooth lying on
the lower jaw, angular IIRC, the second one is probably still in it's
place and is directly left to the former one.>

  Examination of this region shows me that there are no teeth but one end
of a rectangular, flattened bone likely belonging to the palate that
underlies the posterior dentary and overlies the jugal/lachrymal contact;
one can surmise that the strap-like element within the external mandibular
fenestra is a continuation of this. Its shape suggests it is one of a pair
of vomers. Immediately rostral or mesial to this element is a short,
elongate basally triangular element that is flat and expands abruptly
towards the base rather than gradually. This may be a part of the medial
mandibular bones, possibly the prearticular or coronoid. The same region
on the positive slab yields no indications of teeth, despite exposing the
medial surface of the occluded jaw. The dorsal margin of the occluded
lower jaw of the positive slab in fact bears a few longitudinal bones that
may represent the coronoid and prearticular as irregular outlines and a
strap-like element visible lying atop the external mandibular fenestra. I
still declare there are no teeth in *Scansoriopteryx*.
 
<Does this mean that Scansoriopteryx only had teeth on the lower jaws?
Nope, the entire facial region on the skull is missing, so it probably had
a full set of teeth in both it's upper and lower jaws, this in contrary to
Epidendrosaurus IIRC, who only had bony bumps on the lower jaws.>

  Problematically, a maxilla is absent in both specimens, and in
*Epidendrosaurus*, several well-defined teeth (not bumps) are present in
the rostral half of the dentary, and without utilizing Adobe to examine a
less-than-ideal photograph, one can only trust the opinion of the authors.
The figure, as stated above, is of too low a resolution to offer much help
on the matter.

<ps. I have to agree with HP Mickey Mortimer that Scansoriopteryx is
indeed the cooler/ sweeter name if the two turned out to be synonymous...
:)>

  This matter of coolness is still irrelevant, and one can opt for
whichever name one might wish, but the nature of a name is subject to
rules of priority. If they are synonymous, *Scansoriopteryx* goes, at
least as far as _Naturwissenschaften's_ statement of publication date
stands, and one cannot choose which name one would want instead of another
when faced with the problem. Similarly, despite the similarities noted by
Mickey Mortimer, many of which are shared by other taxa, these support
only that the two taxa are closer to one another than either is to any
other taxa. The degree of similarity is banal, as it requires a
subjectivity that must, at least to some degree, be discarded; use of a
genus still requires one to define a genus separately from taxonomic
usage, otherwise it is meaningless in a genus/species set. The idea that
only species are real and that they may be represented by binomina is a
young one, and one which I find favor with, and if there is any difference
between the two specimens, then this may offer a reasonable certainty that
*heilmanni* and *ningchengensis* are indeed rather separate, if similar,
organisms.

  Finally, in response to Mickey Mortimer's problem with my orientation of
the frontals, my use of *Epidendrosaurus* as having a "side-on" frontal
was further elaborated in the sentence as a dorsoventral view of the
specimen, not from the side, which I miswrote. In *Scansoriopteryx*, the
frontals are preserved obliquely, not dorsal side down, as they are in
*Epidendrosaurus*, reducing the shape comparison and the degree of dorsal
convexity apparent, as I discussed when *Scansoriopteryx* and
*Epidendrosaurus* were both first described. Degrees of fusion in the
braincase elements between the two differ also, with more fusion in the
former than the latter, and it would be questionable to indicate either
are at the same ontogenetic stage, despite similar sizes.

  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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