[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: DinoMorph Strikes Back!... or does it?



(Posted for Kent Stevens.)
_____

A few comments regarding Gregory S. Paul's (GSP's) communication:

1) I agree with GSP regarding: [for all sauropods to have low-slung necks] "... it's not impossible, but it's really odd". Sauropods were probably very odd indeed, and not fitting nicely into some preconceived notions. Specifically, for such large terrestrial vertebrates to have such long necks and not go around holding them nearly vertically, giraffe-like ... I can see how that would rub some people the wrong way.

2) For those unfamiliar with the juvenile _Camarasaurus_ CM 11338 from personal observation, I have posted some pictures that clearly show how the neck is preserved in a hyper-dorsiflexed pose. The zygapophyses are clearly disarticulated at most intervertebral joints. This fact should not be a matter of argument or artistic disagreement. The postzygapophyses are translated caudally as a consequence of dorsiflexion to the point they are physically wedged tight against the ascending neural arches of the more caudal cervical. For those of you that have only seen photographs (or drawings) of this specimen in lateral view, the photographs should be informative and settle any doubts that might remain as to whether this juvenile is preserved in a comfortably achievable happy-young-sauropod-out-for-a-stroll posture.

You may find the newly introduced images by selecting Camarasaurus (from the second menu from the left) on the following site:

http://www.cs.uoregon.edu/~kent/DinoMorph

then scrolling to the bottom and clicking the link to CM 11338

or just look directly at them here:

http://www.cs.uoregon.edu/~kent/DinoMorph/Camarasaurus/CMNH11338.html

3) Regarding the remarkable _Camarasaurus_ specimen with two fused vertebrae (AMNH 5761/X-a-5-605). Just look at them. They sure seem to be in collinear alignment when you are right there in the big bone room at the AMNH looking at them. The pictures kindly taken by Rick Edwards and facilitated by Carl Mehling convey much of the story. Here are shortcuts to the images:

http://www.cs.uoregon.edu/~kent/DinoMorph/Camarasaurus/images/AMNH/5761a-
02.jpg
http://www.cs.uoregon.edu/~kent/DinoMorph/Camarasaurus/images/AMNH/5761a-
03.jpg

4) In the 1999 Science article Mike Parrish and I published, the manuscript originally included data for 25% and 75% overlap as well as the 50% overlap, but the other estimates were dropped in the editing in order to save column inches. But curiously the height results for 25% safety factor were rather similar to those for 50%, for reasons that seem to escape GSP: to raise the head (and NOT merely curl the neck into an arc), almost all the dorsiflexion must arise at the base of the neck. The mid neck, and especially the cranial few cervical vertebrae must remain STRAIGHT in order to maximize the elevation of the head. So the large number of cervical vertebrae don't really enter into how high the head can raise. One cannot trivially multiply (say) 5 degrees per joint times 18 joints (= 90 degrees) and conclude the neck forms a right angle with respect to the trunk of the animal. What would result is an arc of diminishing radius of curvature (because centra length diminishes cranially). Such simple numerology does not yield the desired giraffe-like neck, the kind with a sharp kink at the bottom and a derrick-like ascent. To get a giraffe-like neck requires specialized vertebral morphology at the base of the neck, which informally we call "wedge-shaped" or "keystone shaped". Incidentally, some dinosaur illustrations (particularly of camarasaurids and brachiosaurids) show both a sharp upturn at the base AND an inflection point at mid neck (i.e. an overall sigmoid or reflex curve). In order to create a reflex curve, the cranial portion of the neck must be ventriflexed and the caudal part dorsiflexed (if they are not already so-disposed in their osteologically neutral pose, as in the horse, and the avian neck, for instance). Trying to put a swan-like sigmoid curve in a sauropod neck, one ends up with a disappointingly low-amplitude sigmoid curve (unless, of course, one disarticulates the vertebrae where necessary to create the desired curve).

5) Sorry, but I must reiterate that when compositing original published illustrations to reconstruct a vertebral series, one needs to be mindful of the fact that 1) the vertebrae are sometimes not depicted in correct scale within the original document, and 2) some bones are crushed and significantly distorted diagenetically. The first issue induces artifactual curvature, leading to the false impression of a truffle-hunting, or gopher-hunting sauropod in osteologically neutral position. I hope this red herring doesn't keep rearing its ugly head, to mix metaphors. The second issue, attempting to place a distorted vertebrae into close articulation with its adjacent vertebrae, is simply silly. For that reason, I pay careful attention to the image scale of each vertebra image, and secondly, place any distorted elements with caution, using the adjacent vertebrae as an overall guide (such as I did regarding the noted sixth caudal of _Apatosaurus_ CM 3018 from Gilmore, some _Dicraeosaurus_ presacrals, and the mid-cervicals of _Diplodocus_ CM 84 that cause a downturn which Mike Parrish and I checked by manipulating casts of the originals, and concluded is due to distortion). The photo-composites, therefore, indeed leave some gaps where frank distortions arise in the component vertebrae, so that the educated eye can clearly see the distortion for what it is.

BOTTOM LINE: the osteological adaptations used by extant vertebrates to induce neck curvature, and specifically to elevate the neck, are absent in all the sauropod specimens we have thus far examined. Find us some wedgies, and we'll be delighted. Otherwise, the sauropods all seemed "odd" indeed: long necks hanging way out in front, about horizontally, maybe a droopy like that of "Eeyore" (reconstructed so artistically, and yet accurately, by E.H. Shepard for A.A. Milne's Winnie the Pooh).