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

[mkirkaldy@aol.com]

Reposted for Kent Stevens.
___________

On January 3, 2006 4:05:16 PM PST GSP1954@aol.com wrote:

(GSP) < arm posture used by giraffes and okapis). Now, if some 
sauropods had to partly disarticulate the cervicals to get the head 
down far enough to drink then it looks like they did so. As long as a 
joint is not bearing a major load of the body, i. e. a leg joint when 
on the ground while walking or running, it is possible for some joints 
to regularly partly disarticulate in order to achieve a normal function 
(the premeire example being the wrist of the horse). >

Ah, the horse wrist.  Some of us remember your admonishments in an 
earlier DML posting regarding said horse wrist.

But do you know of an intervertebral joint that can be disarticulated 
(more than once)?

As it seemed to Jeff Wilson and Paul Sereno at an SVP talk, it might 
appear that camels can dorsiflect their necks so far they seemingly 
must disarticulate.  But as Mike Parrish and I have subsequently shown 
in our chapter in the Currie Rogers/Wilson volume, it's simply a camel 
thing.  When flexing their necks back sufficiently to rub their 
occipital glands on their shoulders (a specifically male camel thing 
apparently) all cervical vertebrae remain comfortably in articulation.  
They not only preserve a safe overlap at the zygapophyses, but as we 
also show, there are osteological stops that prevent disarticulation 
when the postzygapophyses travel posteriorly to the max.  Hence camels 
can achieve the same degree of dorsal flexion as occurs in the death 
pose.  Not so with poor sauropods, by the way.  Their death pose 
exceeds articulation, and thus probably exceeds what they could 
comfortably achieve in life.  Sorry, but the juvenile _Camarasaurus_ CM 
11338 is probably preserved in a death pose, unless you believe that 
they could go around with their necks all out of articulation.

Going back a decade, at the New York SVP, in the question period after 
a talk I delivered with Mike Parrish, you suggested that I verify the 
DinoMorph method using a modern analog, such as the giraffe.   Well, 
this last year, as part of the "Dinosaurs:  Ancient Fossils, New 
Discoveries" exhibit, the AMNH kindly CT-scanned an entire giraffe neck 
and I put that digitized morphology data into DinoMorph, and yes, the 
virtual giraffe closely replicates the range of motion observed in 
living, behaving, giraffes (look at the movie on my website under AMNH, 
or better, go to the exhibit and run the software interactive for 
yourself)  Moreover, I've found the giraffe neck is osteologically 
braced when laterally flexed to its limit, much as the design in 
_Diplodocus_ and some other sauropods (for mediolateral flexion, not 
dorsiflexion, mind).

Thankfully, one simply does not need to postulate sauropods undergoing 
disarticulation.  The "Eeyore model" of sauropod neck posture, depicted 
in an early drawing of a rather dejected _Diplodocus_ in Hatcher, later 
in an Osborn and Mook silhouette illustration of _Camarasaurus_ (see 
the Bozeman SVP presentation PDF at my site), is pretty much what the 
bones dictate.  Sorry.

(GSP) < Kent said that the dorso-cervicals of AMNH 5761 are fused in a 
straight line.  Actually they are fused in a modest upwards kink, >

Sigh... please look again... it should be plain to see that the 
articulation at the two consecutive centra is indeed straight. This, at 
least, should not require an infinite loop of argument. For driving 
instructions, either go my DinoMorph website:

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

and in the "research projects" pulldown, select Camarasaurus, then 
either 1) optionally read a bit of the text there, including 
instructions on three ways to get a Camarasaurus erect, or 2) just 
click on the link to the pictures, or 3) just click below and forget 
reading all the text:

[note that some pc mail programs will not interpret the following URLs 
correctly if they wrap the URL onto two lines. In that case, you may 
have to reconstruct the url in your browser by hand.]

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

Warm thanks go to Carl Mehling for the hefting and Rick Edwards for the 
clicking.

(GSP) <At the opposite end of things, a number of Camarasaurus and some 
other sauropods of course have the necks in a vertical position, with 
all cervicals still in full articulation even though they are at their 
maximum dorsal retraction. >

I'd like to see such specimens.  Please provide us all with specific 
specimen numbers and institutions.  For those who have actually studied 
CM 11338 (either by getting up on a ladder or visiting either Dinosaur 
National Monument or the Los Angeles Museum of Natural History casts 
thereof, which are at eye level thankfully), it is patently obvious 
that the poor juvenile in its death pose is preserved dramatically out 
of articulation at the zygapophyses!  There's a lot more going on 
there, including a torsional disarticulation at the base of the neck 
which much have lead astray at least one paleoartist.  The same is true 
of a lovely specimen at the Sauriermuseum Aathal, which sure looks like 
it's trying to be a "Juraffe", but for the fact that the neck is 
twisted axially 90 degrees, which is easily misinterpreted visually as 
suggesting a 90 degree vertical bend.  It becomes obvious only when you 
note that cranially the vertebrae are viewed in lateral aspect, while 
caudally the neck vertebrae are seen in dorsal aspect;  something not 
obvious to a casual observer.

(GSP) < People forget that because sauopods had so many cervicals that 
just modest rotation between any two of them adds up to a lot of total 
flexion.>

We're not forgetting.  We also don't forget that there is less angular 
flexion per joint permitted by the proportions of the zygapophyseal 
facets relative to their centers of rotation in sauropod design, unless 
of course one hypothesizes that the vertebrae were routinely capable of 
disarticulating during everyday neck flexion.

From giraffes and camels to turkeys (and presumably sauropods) the same 
biomechanical principles hold, and seemingly (but the following is not 
sufficiently established yet) perhaps the same safety factors apply 
(e.g. in terms of amount of overlap). We've simply applied the same 
safety factors to the sauropod geometry.  Don't blame us that sauropod 
osteology does not permit swan-like flexibility.

(GSP) <there is no good reason to conclude that such sauropods (and not 
all sauropods are like this) when alive could not raise the neck 
vertically to high browse or get the maximum view of the landscape.>

Yes there is:  the cervical vertebral osteology does not permit such 
extreme dorsiflexion without disarticulation.  Is there an echo in here?

(GSP) <What I am getting at is that an odd view has developed, one that 
seems to think that the only way to legitimitely illustrate or mount 
dinosaur skeletons is with the cervicals in perfect neutral 
osteological articulation. There is no such law.  ... >

But what if such illustrations nonetheless depict the vertebrae as 
undeflected (based on close examination of  the articular facets along 
the axial skeleton)?

For instance, examine the _Apatosaurus ajax_ mount at the Yale Peabody 
Museum.  The neck is mounted in a lovely, gentle sigmoid curve.  Looks 
great.  Now, look carefully at the zygapophyses (take binoculars, or 
borrow a ladder as Mike Parrish and I did) and you'll see that the 
zygapophyses appear to be in neutral position.   But before you 
conclude that this specimen has an intrinsic swan-like curve to it, 
just tap on the vertebrae and you'll find a whole lot of plaster 
artfully stained to resemble bone.  That is to say, those vertebrae at 
the base of the neck where the upturn presents itself were 
reconstructed artfully (I use the term "artfully" again, Scott, in the 
meaning I intend, not merely as suggesting a subjective, aesthetic 
sense of art).  How did that happen?  It seems the available fossil 
material was first attached to a smoothly curved armature, then the 
missing pieces were filled in with plaster, and it just so happens that 
the way the prezygapophyses were plastered in to align directly under 
their associated postzygapophyses, the overall neck appears to be state 
of neutral deflection.  Sigh.

So, regarding laws, perhaps there should be (if there is not an 
unwritten one already) a law stating that if an axial skeleton is 
formally drawn (or mounted) for scientific purposes, as depicting OTHER 
THAN the "perfect neutral osteological articulation" then said state of 
deflection should be accurately and clearly apparent by examination of 
the articular surfaces.   There should also be documentation, perhaps, 
suggesting that the artist intends on depicting the given axial 
skeleton in a state of deflection out of the neutral pose, if that is 
not made sufficiently clear by the intervertebral joint facets.  Such 
cautions are not needed, of course, with the appendicular skeleton: the 
limbs are often drawn as in mid-stride, without the potential of 
misleading the viewer.

Since so many colleagues, when referring to silhouette drawing in order 
to derive an overall understanding of an extinct animal's bauplan, 
tacitly assume that the depiction of the axial skeleton reflects its 
characteristic curvature (as is the way skeletons of giraffe, horse, or 
deer, etc. are traditionally drawn or mounted), there should indeed be 
a law.  Thanks for suggesting it.

Kent