Re: regarding the naris on pterodacs

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

Dave Peters (davidrpeters@earthlink.net) wrote:

<http://www.pterosaurinfo.com/amnh1942_snout_recon.html

shows my take on what appears to be happening on a very tiny, early
pterodactyloid, AMNH 1942. Perhaps the external naris was separate from the
antorbital fenestra in this case.>

  While Dave said it best ("Crushing shifts elements and breaks thin bones"),
this kind of statement should be the #1 reason to not use this technique to
support such conclusions.

  However, I am going to agree with Dave here that his external naris as
identified in the skull is, in fact, part of the external naris. It is my
interpretation that the skull represents just one side of the skull, split down
the middle (this happens in other fossils, too, where half of a skull or even
half of bones will end of on the other slab); in this case, most if not all of
the snout is seen in medial view, and other portions of the skull may be seen
in lateral view. Bones lying between the "nares" and "antorbital fenestra"
[aof] in the tracings and skull photo are, in fact, medial palatal bones and
give the impression of the lateral surface of the skull. I could be very wrong.
On the dorsal margin of the aof, the nasal (in grey) is preserved with a
ventral, premaxillary ramus, and rostral to it is a splint (in maroon) that
dave illustrates as confluent with the dorsal margin of the nasal, and
underlying the premaxillary dorsal ramus (in yellow). I will argue that the
main body of this marroon element is still the premaxilla and that the rostral
maroon split is part of the grey nasal, and in fact represents the anterior
splint of the nasal underlying the premaxilla which has overgrown it. Elements
in orange and maroon lying within the en/aof cavity are probably either palatal
elements or portions of the lateral surface of the skull, or (as in the case of
one region in the top panel (in orange) formed from the impression of a bone on
the other slab OR simply an artifact of the dendrites rampant on the fossil.
Dave illustrates the jugal (in blue) as possessing an rostral ramus which lies
to the side of the maxilla and, rostrally, appears to overlay the toothrow;
here, I suggest this is an artifact formed from the medial dentigerous wall of
the maxilla as seen in medial view, and that there is no jugal splint. In fact,
the jugal's anteriormost expression in the jaw appears to end in the photo at
the level of the blue element (epipalatine) which would appear to lie
underneath the bar. If my interpretation is correct (and ignoring the
"disarticulated" epipalatine for a moment*), nothing extraordinary has taken
place and the external naris is confluent with the antorbital fenestra so that
the entire aperture in the photo expresses from the anteriormost opening to the
jugo-lachrymal bar anterior to the oribt (in which an actual, bony scleral ring
is apparent, with a circular margin that Dave illustrates, but does not color
completely but is confluent and likely represents the remainder of the ring).

 [*] The disarticulated epipalatine, btw, appears to in it's rostral extent,
lying just approximate to the mandible, a series of regular features that I
could interpret as teeth. This would imply this feature is a maxillary
fragment, and the reason we are permitted to see the medial maxilla I
mentioned; the maxillo-jugal bar is incomplete, with the maxilla lying
underneath its own posterior half, but above the far maxilla. That the matrix
within the en/aof appears in relief compared to the bone dorsal to the aperture
and rostral to it, suggests however the remainder of the lateral premaxilla is
not actually present, at least on this slab.

  Thus I would conclude nothing extraordinary is present in this skull, but
that Dave is right in that the anterior portion of the aperture represents the
external naris, but not likely to represent a complete, intact, and separate
external naris.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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