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



Forwarded from Kent Stevens. DV

Begin  forwarded message:


From: GSP1954@aol.com
Date: January 3, 2006  4:05:16 PM PST
To: dinosaur@usc.edu
Subject: Re: DinoMorph Strikes  Back!... or does it?
Reply-To: GSP1954@aol.com


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.


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:


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


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


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.


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.


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?


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