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re: Defending Photoshop



David Peters (davidrpeters@earthlink.net) wrote:

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

  The authors do not contend the animal is not a crurotarsan, so the presence
or lack of prefrontals is immaterial to their study. However, we are also
fortunate that the illustrations were made with the fossils at hand and not
through the benefit of an indecent photo for the purpose as the one in the
figures. 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. Yet the authors show that there was a strongly interdigitating
arrangement of the postorbital and frontal, and the lack of such a contact
between prefrontal/lachrymal and the frontal/nasal. This surely is the result
of examining the multitude of cracks and finding that a sinuous,
interdigitating array of "cracks" probably represent a suture pattern. 

 
<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.>

  The authors in their restoration gave a generalized idea of the arrangement.
As in *Shuvosaurus*, however, the skull had a more "dinosaurian" arrangement
and the postorbital's contact is not unusual at all ... for a dinosaur. The
jugal and quadratojugal are absent, but known in *Shuvosaurus*, and the
position of the quadrate (based on the length and extent of the ptergoid and
palatine to the interconnecting bones) is also based on *Shuvosaurus*. This
means, as the authors state, the postorbital/squamosal contact is probably
normal, and the occiput was rotated ventrally.

<In dorsal view the rostrum has a 90º divergence angle and the rami appear
rather straight, but the reconstruction rounds it. Maybe the ventral view shows
this better.>

  The skull has been dorsoventrally crushed. The restoration doesn't help in
essentially keeping much of this distorted width. Nonetheless, the skull was
likely a good deal narrower, and the shape of the ventral (tomial) margin of
the premaxilla was curved as occurs when the two halves of the skull are
rotated ventromedially into a more "perfect" arrangement. This is, of course,
completely subjective, but there seems a bit of experience in examining
distorted skulls to consider the reconstructive models.

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

  An effect of the size of the skull, as in species of *Araripesuchus*.

<an offset femoral head,>

  As do most bipeds.

<lacrimal separate from frontal,>

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

<posteroventral rotation of squamosal,>

  In this case, the squamosal as in *Shuvosaurus* is anteroventrally, not
posterventrally, rotated, as is the quadrate.

<the posterolateral/ventral portion of the pmx is greatly reduced.>

  What portion is that? The corpus, main body without the processes?

<Like Effigia, Aetosaurus has the anteroventrally rotated quadrate, the
anteriorly elongated ilium, tiny manus, enlarged naris, brevity of the dentary,
length of the mandibular fenestra, reduced premaxillary teeth, ascending
retroarticular process.>

  GSP even made a comparison of aetosaurid skulls with *Erlikosaurus*, with
some interesting, and favorable interpretations. Unlikely given their nature as
maniraptoran theropods of a highly derived nature, but interesting nonetheless.
However, several other issues of the limb anatomy of any aetosaur shows that
the forelimbs were heavily weight-bearing, the manus is not so much as tiny
compared to the arm as it simply is to the foot. Nesbitt and Norell show that
the manus is INCREDIBLY small compared to the forelimb itself, a feature one
also sees in bipedal ricochetal mammals such as the grasshopper mouse or
jerboas, in several hypsilophodontids (which are also notable for having a
forelimb so completely smaller than the hindlimb, as in *Effigia* but not as in
aetosaurs), and that the forelimb and hindlimb design feature non-offset capiti
of the epipodials, a sprawling and not linear arrangement between epi- and
propodials, etc.

  On the restoration, however, it is not possible to observe in the fossil the
morphology of the mandible, so how much of this is real is unclear. Thus the
"brevity of the dentary, length of the mandibular fenestra ... ascending
retroarticular process" are not actually observable. In the latter feature,
ascending is relative to the shape of the posterior mandible, while 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, and
*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.


<Were armor plates or scutes found? I overlooked the note if so.>

  They were not recovered, and given the fauna, armor plates tend to be found
more than BONES are, so there is a good chance there were no scutes present.
That same is true for most rauisuchians, including all other poposaurs.

<To move Effigia closer to aetosaurs requires one more step. To move it to the
base of the Ticinosuchus + aeotosaurs requires 5 more steps. To move it close
to Lotosaurus requires 13 more steps. The clade Ticiniosuchus + aetosaurs is
the sister to the Archosauria,which includes Turfanosuchus + (Dinosauria +
Crocodylomorpha).>

  This is only because you've reinterpreted *Lotosaurus* as a dinosaur. Given
my comments on that when this issue came up, one should be very circumspect
when non-dinosaurian vertebrae, non-dinosaurian scapulae, non-dinosaurian limb
bones, all point to a non-dinosaurian but crurotarsan *Lotosaurus*. But go
ahead and publish findings on detailed photos of the original material, if it
passes peer-review. I suggest having Clark and Wu work as reviewers.

<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.>

  Once again, PAUP has done nothing but applied YOUR subjective data to an
algorithm. These programs used, PAUP or Photoshop, are simply tools, and have
no value otherwise, nor any particular value in any result that does not
distill down to the input data.

Jaime A. Headden

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

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