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Re: Did dinosaur wings evolve for breeding display?/Longisquama



Well said, Jaime.

That being said, I had the original in my hands also.

David


On Apr 22, 2009, at 5:45 PM, Jaime Headden wrote:


I would like to close my current discussion on this topic with my opinion on my use of photographs:


Photographs are photographs, and they represent a finite level of detail no machine or technology can increase (not without the original negatives, and certainly not without considering the resolution the negatives are produced at themselves) and when read on a digital machine, everything is rendered in pixels, which REALLY restricts artifacts. Whereas before you have ink/laser artefacts that reduce fineness of detail at the microscopic level in which some of these photos must be read (as a book, in cases), on the computer you have to see that a pixel contains no subpixels of information that can be gleaned, decoded, aliased, or whatever, no matter the technology of the tool. When you have a digital reproduction of a physical artefact like a photo in which the lighting is skewed, and the resolution weak, you are introducting layers of problems in interpretation into your image and what ever you want to get out of that image must come according to the restrictions therein. So much is not visible in a photograph that the original is ALWAYS superior, and even a cast is dependant on the fineness of the casting material (in two degrees, the material used to make the negative from the original, and the material used to create the positive copy that is the cast itself).

This is the world I enter when I use ANY photographic sources to produce any skeletal, and it often means a lot of guesswork (skull bone shapes, positions, vertebral shapes, positions of apophyses on vertebrae, etc.) which influences the final product (if I can get that far) to the point that it is not possible to make a perfect skeletal, a perfect skull image, or even assure yourself of the detail to which you would like, even if it's critical that you have that detail. I had the opportunity to examine (briefly) a cast of the holotype of *Longisquama insignis*, and it was this brief episode that has cemented my understanding of the slab and all that it can reveal:

There are holes in the slab created by imperfect splitting into part and counterpart, where chunks of material were separated from the slab everyone sees now, and there are portions of the slab which are irregular unworked surface but show dips, ridges, and rolling hillside that would remind anyone of the lovely nonflat countryside in northern England and Scotland. This slab does not, and cannot, preserve material hidden to the untrained eye or photograph at much of any lightning because, in most cases, the slab isn't there to expose this information. The animal is extremely small, although not as small as some intriguing fossils (an entire conodont apparatus can fit on the head of a pin ... I sympathize with the people who prepare and investigate this material first hand), and even the resolution of the cast shows that there is unconformed crushing and smushing in the skull and shoulder, and in fact any portion of the skeleton where a bunch of bones are layered atop one another. The finest and most perfect detail in the slab are in fact located on the structures that radiate outward from dorsal to the spine, attached or not, and this detail is still lower than the fine details of sutures and contacts among cranial bones, and much less detailed than the fineness of the dentition, which as far as I can tell are just slightly curved cones.

My skeletal of *Longisquama* is, was, and will continue to be nothing but rampant speculation compared to the detail I could glean from a 10 foot long mount of GIN 100/42, currently referred to *Citipati* sp. and one of my favorite fossils ever, and certainly deserving of its own specific monicker when it is fully described.

Cheers,

Jaime A. Headden

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

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David Peters davidpeters@att.net