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Photoshopping Techniques and Tracing



Paul Sparks' comments and Tim's consideration of a method, as well as various
conversations about the viability of reproducing the method David Peters has
used to infer his reconstructions and findings, has needed some back up. David
Marjanovic took some portions of Dave's reference material and found some
irregularities, as has Chris Bennett. 

  Furthermore, Silvio Renesto has reconstructed the skull of *Megalancosaurus*
and has not reproduced Dave's findings in this animal. Dave's reconstruction
can be found here:

  http://www.pterosaurinfo.com/megalancosaurus.jpg

  While that of Renesto can be found in Renesto and Dalla Vecchia:

  Renesto, S. & F. M. Dalla Vecchia. 2005. The skull and lower jaw
   of the holotype of *Megalancosaurus preonensis* (Diapsida,
   Drepanosauridae) from the Upper Triassic of northern Italy.
   _Rivista Italiana di Paleontologia e Stratigrafia_
   111(2):247-257.

  To which Dave has responded about issues detracting from that reconstruction
due to a differently interpreted dorsal braincase:

  http://www.pterosaurinfo.com/meg-frontal.jpg

  This shows two quite similar techniques arriving at very different
conclusions, such that Renesto recovers a narrow L-shaped frontal and no
antorbital fenestra, while Dave finds a broad trapezoidal frontal and a large,
distinct frontal. There are many problems with dealing with the dolomitic Upper
Triassic fossils of Italy, in that some slabs (the holotype of *Megalancosaurus
preonensis* is no exception, but educational in this regard) are split
unevenly, not perfectly, so portions of both sides of the bone inclusions end
up on both slabs, and in this case, we have the posterior processes of the
premaxillae on both sides of the skull clearly paired, as are most other bones
in the skull, which has led to Dave inferring a space between them by
interpreting both of these processes as belonging to the same side of the
skull. This conclusion does not arise because of the methodology, but because
of the interpretation of the material that is drawn from it, so one should not
fault Photoshop for the effectiveness, merely a consideration of the material
at hand.

  Photoshopping to develop some ability to determine what a flattened slab
might show can be used in various corners, for various purposes. Mickey
Mortimer here has used it to outline the skulls of various Liaoning birds, with
a general aversion to over interpreting features in the bone, for the sake of
finding general bone shape, which for his purposes is to determine general
measurements and qualities of the skull. Here is *Abberatiodontus*:

  http://dino.lm.com/images/display.php?id=1944

  and a dinosaur, *Sinosauropteryx*:

  http://dino.lm.com/images/display.php?id=1833

  Finally, I have also used Photoshop and to some high resolution to determine
the shapes and inclusions onto a "tracing" so as to evaluate it without the
distracting shapes around it on the slab.

  http://i16.photobucket.com/albums/b1/Qilongia/Archaeopteryxpropatagium.jpg

  In this illustration, I have collected images of some high (and some lo) res
illustrations and photographs of the mainslab of the Berlin *Archaeopteryx* in
order to consider the question of a preserved propatagium, the differentiation
of crack features, feather impressions, and tooling traces, which will all
obscure one another. As I hope to show, there probably IS a propatagium, with a
line of feathers across the shoulder to the mid-forearm on both sides, the
left-hand wing is covered in oblique tooling traces likely used to remove
surface limestone from the impression surface, and the impressions of both
flight feathers and coverts, some of which cross over the forearm and might
actually be secondaries that have been deflected from below the arm to up and
over it. Such things happen with extant bird carcasses I have observed, and
this animal should be no different. Finally I should note that Darren Naish,
who's illustration I have "borrowed", has also seen these features, and they
are illustrated to support this consideration.

  Using this technique is valuable as it gives you a different way to look at
the material; the problem arises from expecting too much from what you see, and
using it for anything more than a presentation. All of the features I describe
I could see with the naked eye without the aid of Photoshop, and I used no
lighting or resolution or contrast changes to draw on these photos, and use
them only to illustrate what I saw without such "aids".

  I have seen other fossils with odd associations of bones, and have attempted
to tease out their shapes in order to better understand them, such as the skull
of *Scansoriopteryx heilmanni*, and have done a Mickey Mortimer-style tracing
to make these observations cohesive. Nonetheless, he and I have seen the same
slab and come to different conclusions about the material, and this explanation
comes only from the a posteriori observation and interpretation, and not from
what's actually on the slab or what can be seen (we both admit to seeing the
same impressions, the same knobs and thingamajigs). The only answer is that we
see the end conclusions differently, and this comes from experience and
interpretation of data, which tends to be very subjective. So I hardly think
I'm right on this matter.

  The only conclusions in these practices that I can conclude is that we should
not be using the tracings as a fact-finder; they are an illustrative technique
only, and given access to the actual fossils, I would never use them to "see"
anything. I did have access to a cast of *Longisquama* once, and the nature of
the slab's irregular fracture plane shows me what a flat plate could never have
done, and I offer this as a cautionary tale.

  http://www.pterosaurinfo.com/longisquma_winglets.jpg

  In this, looking at the actual slab, I cannot for the life of me see any
extensive digits coiled around the bottom of the slab. I have looked. When I
had access to the cast, I put my face nearly touching it to peer for the
missing material Dave has seen, and I cannot for the life of me find them. My
conclusion to date can only be that they are not there, and I have no other
reason to assume this except that they do not appear to be present in any
distinct form, nor can I figure why the arm and manus as preserved, which
others have illustrated, can possibly offer further material with differential,
and vague impressions.

  Cheers,

Jaime A. Headden

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

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