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Re: Defending Photoshop



----- Original Message -----
From: "Jaime A. Headden" <qilongia@yahoo.com>
Sent: Sunday, February 05, 2006 4:08 AM

David Peters (davidrpeters@earthlink.net) wrote:

<The postfrontal is probably present. Two identical 'cracks' suggest so. They
extend almost to the prefrontals.>

The cracks are not symmetric on the two sides of the skull. This doesn't prove there is no separate postfrontal, but I can't see any evidence that it's not absent (or fused to the frontal -- certainly not to the postorbital, though, which is the most easily imaginable possibility for how the dinosaurian condition came about).


Indeed, how one could tell the cracks in the crushed skull from an
array of associated circum-frontal bones versus a single, cracked frontal, I
have no clue.

The photo starts to blur at 400 % magnification. It is not possible to discern the interdigitating parietal-frontal sutures there that are shown in the drawings. The actual fossil could have higher resolution...


<The postorbital portion of the skull is rounded posteriorly and appears to be
rotated ventrally, so the upper temporal fenestrae open more posteriorly.
Norrell and Nesbitt 'fixed' it in the recon. When left alone the jugal
descends.>

It would certainly help if the jugal were preserved...

<Like Effigia, Ticinosuchus also has an enlarged orbit,>

Test this character for phylogenetic signal. I predict it will barely have any because it's so strongly size-related that it varies a lot in ontogeny.


<an offset femoral head,>

As do most bipeds.

Most animals with vertical limbs?

<lacrimal separate from frontal,>

As do all non-avian -- what, sauropsids?.

Osteichthyans?

[...] the length
of the dentary is relative; how short is "brevity"? In aetosaurs, the dentary
if 50% the mandibular length, this animal has one incredibly shorter,

Here we may be dealing with a continuous character. Current phylogenetics programs can't deal with this (or what does TNT do?), so you need to turn it into a discrete character by breaking it up into discrete states. How many states to use, where to draw the lines, is a subjective decision if the character is truly continuous. But if there are obvious gaps in the distribution (there's certainly a statistical test for this somewhere), there may be obvious places for drawing lines. Someone should find out if there's such a gap between the dentary lengths of aetosaurs and *Effigia*. -- But the more continuous a character is, the more obviously it should be ordered anyway.


*Shuvosaurus* doesn't clarify either the size or extent of the external
mandibular fenestra OR length of the dentary. And reduced premaxillary teeth?
This animal is _edentulous_, and thus does not share ANY feature of the
dentition or dental arrangement with aetosaurs.

Except if there's an ordered character along the lines of "pmx teeth large (0), small (1), absent (2)" in the matrix. -- Whether such a character should be ordered, however, is not quite obvious. Either way one is forced to make an a priori assumption about evolution.


<Would have been interesting to see the strange mandibles, but they were only
reconstructed. This also gives kudos to PAUP which identified a sister taxon
relationship between two overall and at first glance unlikely sisters.>

This boils down to nothing more than "in order to be the next Galileo, it's not enough to be persecuted by an orthodoxy; you also have to be right" -- Carl Sagan (probably not an exact quote). In other words, if this relationship turns out to be defensible, it's good for PAUP*, and if it's not (as PAUP* itself may show if it's fed more and/or better data), it's not.