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



Scott "I Have an _Archaeopteryx_ and You Don't, Neener Neener Nee-ner" Hartman wrote:

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.

Well, I think it may be symptomatic of the natural, human tendency to greatly prefer a single "cause and effect" explanation over anything that involved multiple variables. This has happened any number of times in paleontology (e.g., bolide impact = extinction, extinctions = bolide impact). Sure, the "long neck MUST be for getting the head somewhere improbable" solution is tempting -- it makes a heckuva lot of sense! But of course, evolution is rarely that simple -- multiple factors doubtlessly played important roles. One that I like (although I emphasize that I am NOT touting that it is the SOLE reason long necks evolved in sauropods) is that long necks (and tails) are low surface area/volume ratio structures that radiate heat effectively. Sauropods got big, possibly in part as an anti-predator function, but ran into "gigantothermy" issues, thus favoring the evolution of "elephant ear," heat radiation structures. Doing so with the trunk and limbs doesn't make a lot of sense at size, so longer necks and tails it was. Now, having a long neck almost certainly conveyed a number of other benefits that could be exapted -- getting the head up into trees may have been one of them, at least for some sauropods. That, of course, is where work like Greg's, Scott's, and Kent's all play important roles. Still, I'm absolutely dying to make hollow, easily manipulated, fiberglass-reinforced resin casts of some relatively uncrushed sauropod cervicals and thoracics that can be attached with ball-bearings in the condyles and suspended from cables to let me (and Greg, Scott, Kent, or anyone else who wants in) manipulate them without worry about weight, breakage, etc. Such a model could even be caked up with elastic bands (as in the _Torosaurus_ arm experiment) and less elastic straps to examine the limitations muscles and ligaments may have had on movement.


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. <

What I think Scott and Kent are dancing around here is the criticism that has often been leveled at some paleontologists (well OK, at least one that I know of on a repeated basis) that their "reconstructions" (read: drawings) don't accurately represent the fossils they're supposed to illustrate -- there is, shall we say, some creative liberty taken between the "seeing" and the "drawing" processes. Scott is correct that this should always be a concern, so the accuracy of any drawings should be verified against the actual specimens when doing things like Kent has been doing. I do think Kent and Mike Parrish have done this as much as humanly (and financially) possible. Both Scott and Kent are correct in that one does, at some point, have to account for diagenetic distortion, which is frustratingly common in sauropods -- the best looking (read: least distorted) sauropod verts I've ever had the pleasure of laying eyes on personally (long before I had any real interest in sauropods) are those of _Malawisaurus_ (and even those are squishy-ed a little!) -- those are also small, and might be ideal for getting some baseline, hands-on manipulations. Those of _Rapetosaurus_ also look really nice. But I digress...I have had the pleasure of seeing the _Dicraeosaurus_ and some of the African _Brachiosaurus_ verts up close and personal, and there is some, sometimes evil awful bad distortion, and that may be responsible for the disarticulations Scott noted.


To quote Dave Barry, "I'm not making this up". <

Hey, anyone who quotes Dave Barry CAN'T be wrong!

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.

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.

I've also had the pleasure of playing with camel cervicals, and they're actually peculiar in a number of respects. First, the caudal cotyle isn't _nearly_ as concave as the cranial condyle is convex -- it's somewhere between stereotypical "opisthocoely" and "having a ball butt up against a flat surface." I've wondered if this is, in part, responsible for the camel's ability to hyperdorsiflex its neck. Second, the apparent "angle" of the caudal codyle, in lateral view, doesn't reflect very well the nature of the cotylar surface: we tend to assume that the center of any arcuate surface is the point at which a perpendicular crosses through the apex of the arc (e.g., the umbrella model), and while this may be true geometrically, it isn't true anatomically all the time. In some opisthocoelous mammals, the caudal cotyle is basically what one would expect except that there's an extra-long sheet of bone protruding caudally from the ventral margin. In other words, when you look straight into the condyle, along the axis of the vertebra, the concavity seems to be "pointing" more or less along the axis of the vertebra, but when you look at the thing in lateral view, you'd expect that the shaft of the "umbrella" that would hypothetically pierce the arc of the caudal cotyle, you'd think it would be a line that would proceed cranioventrally. I didn't play very much with how they actually articulated -- I was more focused on getting some measurements for other reasons -- but it looked as if the vertebrae lined up with the vertebral long axes closer to lining up that one might thing from such "wedge" or "parallelogram"-shaped structures in lateral view. I haven't thought much about it; it sounds like an interesting adaptation to limit ventral flexion of the neck, but doesn't necessarily imply that the neck MUST have a sharp upward turn. In some non-opisthocoelous mammals (e.g., a warthog whose skeleton I measured), age produces really ugly exostoses that create caudally-projecting ventral (and sometimes even lateral) sheets from the caudal articular surface; sometimes, these even fuse cervical vertebrae together (i.e., they're fused along these ventral sheets, but nowhere else), again limiting ventral flexion. I'm not saying that either Kent or Scott is wrong here; just reporting some observations -- their applicability to sauropods ought to be investigated.


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. ;-)

Nothing in science is ever determined by jury, or by popular vote; just overwhelming evidence for one or another point (as if I had to tell this to anyone on this list!) Kent and Mike have made some really good, and very interesting, in-roads on this question, and I'm glad to see Scott is following up. More sauropod neck work!


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT  84770   USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and     dinogami@gmail.com
http://cactus.dixie.edu/jharris/

"And the role of George W. Bush will
be played by: Ralph Wiggum" -- Conan
O'Brien, during "Earth to America," in
listing the fictitious cast of an upcoming
TV movie about global warming.