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Re: DinoMorph Strikes Back!... or does it? (long!)



Thanks to Dan for making this a more interesting discussion!

I want extend appreciation to Kent for his cogent reply; it made me realize how sloppy I'd been in my own post. The following is my own protracted response the issues he raises:

First of all, I want to say that I'd be delighted if we find a
sauropod that in life had an upturn at the base of the neck. It would be emotionally uplifting, if not merely a pun, to find that not ALL sauropods went around looking like Eeyore (from Winnie the Pooh), all dejected and droopy. <

Frankly, I don't care if sauropods had upright necks or not. I take issue with the improbable energetics of evolving a long, expensive neck to "increase" grazing area, when in fact it's cheaper (and progressively so as you get larger) to simply take a few steps forward (this likely being even more true in the Mesozoic due to the potentially patchy nature of plant resources in non-grassland grazing environments). That said, everyone seems to be in agreement that at least some sauropods (e.g. diplodocids) held their necks outright, so whatever the selective pressure, it did happen, and in theory it could have happened to all sauropods. I am simply urging caution in giving too much weight to a data set (Photoshop manipulation) that I think has problems are (currently) intractable. More on that below.

This is Photoshop manipulation of illustrations; frankly, it's no >
less "artistic" than the other reconstructions that are lamented on > the same page.

I respectfully disagree, and it is not merely a matter of personal taste regarding what is "art" and what is not (or what the definition of "is" is :).

Composting of images is NOT "artistic". Granted it's something that can be done with paper and scissors, like in a grammar school art class, but it's NOT art. <

Ok, perhaps this is a semantics thing; I looked around for a few definitions, and the one that seemed the most relevant (to me) was this: S: (adj) artistic (satisfying aesthetic standards and sensibilities) "artistic workmanship", which can be found at the Princeton online dictionary here:

http://wordnet.princeton.edu/perl/webwn?s=artistic.

Feel free to pick a better definition if need be, but the issue of "satisfying aesthetic standards" seems relevant to me, because it seems to be the underpinning of its pejorative use against competing skeletal reconstructions. Now, despite my ham-handed response, I don't mean that Kent (or anyone using Photoshop composites) are intentionally trying to achieve an "aesthetic" end.Kent himself has indicated an aesthetic preference for not all sauropods to "look like Eeyore", despite the conclusions he draws. But.regardless of the errors they contain, I seriously doubt that Greg Paul or anyone else executing skeletal reconstructions intends them to be anything other than accurate interpretations of the osteology. My point was that since Photoshop manipulation itself relies upon illustrations of bones, it has the exact same source of error, and then adds additional sources (see below). This does NOT mean that I think Kent is wrong and Greg is right; Kent has pointed out some cases where Greg may have misinterpreted the data, and each discrepancy must be resolved on its own merit. While Kent may prefer the method he uses (I would hardly expect otherwise), it is manifestly unfair to dismiss alternate forms displaying the data as "artistic" and therefore ignore it.

A quick aside; ironically, my own most recent skeletal drawings actually use Photoshop compositing. Here is an example of the tail of Supersaurus:

http://skeletaldrawing.com/supersaur_project/tail_composite.jpg

Full disclosure: The tail was not drawn with the aid of the composite; instead the composite was used to check the accuracy (although it checked out quite well). Other portions of the skeletal (look for it in an upcoming paper) were drawn directly from photographic reference, including the dorsal series. The bones were still simplified in terms of detail, because otherwise there would be reproduction issues at smaller scales. I don't know how far I will go with this technique, because we are already trying to explore how to use 3d data to increase the accuracy of 3D portrayals of skeletons (this appears to be necessary for the time being, as 2D delivery media seems to be here to stay).

In creating the digital composites, I used scans of the original
illustrations, at MOST modifying the scale of the images (isotropically, to preserve proportions of the lateral views) so they were iso-scale. Then I placed them in articulation with neutral position simultaneously at centra and zygapophyses. I introduce none of the subtle manipulations of the shape of the centra as one can find in some side view silhouette illustrations. Please look at the silhouette illustrations for Brachiosaurus (on my website under Brachiosaurus, and also available in PDF form elsewhere on the site). Check for yourself the induced wedge shapes in some of the illustrations. To quote Dave Barry, "I'm not making this up". <

Ok, this is starting to get to the crux of the issue. With opisthocoelous vertebrae (yes, that's what I meant, although you have the same conundrum with procoelus vertebrae) "wedge-shaped" is not easily based on centrum dimensions; For example, Greg is not actually introducing much "wedging" into the centra of his brachiosaur cervicadorsal transition. Here, I've done a quick Photoshop T mockup demonstrating it:

http://skeletaldrawing.com/sauropods/GP_brach_cervicodorsal.jpg

(Disclaimer, this is for schematic purposes, and may not reflect Greg's intended interpretation of the centra; you'd have to ask him). With four points for articulation (ok, more actually, but I'll stick with the condyle, cotyle, and left (i.e. visible) pre and post zygapophysis) the geometry of the zygapophyses strongly influences the degree of arching. Has Greg accurately depicted the zygapophyses in the cervicadorsal region? It's impossible to say for Brachiosaurus, of course. Personally, that older upturn in the neck looks too strong to me, but that's nothing more than personal opinion.

I don't trivialize the notion of "wedge shape" by only looking at
centra, and moreover, certainly not to merely looking at their posterior (cotyle) margins. Again, look at our book chapter illustrations, and better yet, please read what Mike Parrish and I carefully wrote on the subject of determining neutral pose curvature. <

And on a related note: >Then I placed them in articulation with neutral position simultaneously at centra and zygapophyses.<

Well, obviously Brachiosaurus is a bad example for this, so let's look carefully at some of the illustrations from your papers and website:

http://skeletaldrawing.com/sauropods/dicreaosaur_arrows.jpg

http://skeletaldrawing.com/sauropods/mamenchiosaurus_arrows.jpg

In both Dicreaosaurus and Mamenchiosaurus the resulting composite clearly shows disarticulated zygapophyses (red arrows). Obviously Kent isn't suggesting that these are in their life position, but how should this discrepancy be rectified? Should we assume that the neural arch has undergone distortion but the centra have not? Articulating the zygapophyses in the Dicreaosaurus Photoshop composite pulls the neck up into a position more closely resembling the original description, (albeit still a horizontal one). Mamenchiosaurus seems to be all over the place, (presumably due to crushing), but there is an interesting pair of extremely disarticulated zygapophyses pairs (labeled 1 and 2) right where the neck is thought by some to arch upwards. Was there differential anterior-posterior crushing on those vertebrae? I haven't seen the original material, so I don't know, but I don't think this kind of think can be satisfactorily tested with Photoshop compositing.

The shape of the condyle may be evident in lateral view, how does one assess the depth and shape of the cotyle in a photo composite? The posterior rim of the cotyle is all that is evident in lateral view. I don't know if it was possible to check all specimens (e.g. Mamenchiosaurus), but even on ones where physical examination is possible, how can someone be sure that the lateral profile through the medial portion of the cotyle is faithfully reproduced? This seems to me to be one of the larger problems, because this is (in part) where the "wedge shape" would be evident, yet there is no obvious way to check this. For example, right in the cervicadorsal transition of the Mamenchiosaurus Photoshop composite there is a condyle that sits a great deal further into the anterior cotyle (blue arrow) than any of the surrounding vertebrae. If the condyle were moved back further as it is in the other vertebrae, and the zygapophyses were articulated, you would have one heck of a giraffe-like upturn in the neck. Perhaps this is simply due to crushing, but how was this interpretation established? Was there a direct observation that leads to the very different cotyle shape on that vertebra as opposed to the ones on either side of it?

For the moment I'll leave the Camarasaurus issue for a future discussion, although I don't think the Annabelle mount is articulated properly. For what it's worth it's the WDC specimens, since we have two showing the same thing. When we get it scanned into the computer, I'll make sure the data is available to play with.

Remembering the jury's verdict on the O.J. Simpson trial and the
Michael Jackson trial, do you really want to use a jury as a basis for determining the truth? <

Well, the only other phrase I could think of was "The results are not yet in." which is a political reference and didn't seem like a much better basis. ;-)

But until the above issues are addressed (and IMHO they are not suitably addressed in the two sauropod volume papers) I have a hard time seeing Photoshop composites as strong evidence for sauropod neck posture.

Cheers,

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(408) 483-9284

www.skeletaldrawing.com