Re: sauropod arm articulations

[GSP1954@aol.com]

When reading Bonnan's paper he more than once made an association between the 
high limb compressive forces in sauropod legs due to gigantism and their 
straight limb posture. I took this to mean he was arguing for a consistent link 
between these factors in all land giants, and therefore I made some 
observations 
to the contrary. He says he was not arguing for universal straight legs in 
giant, which is fine. But, if some land giants do not have straight legs in 
order to cope with the high compression loads of great mass, then why would 
others 
have straight legs in order to do so? Either straight legs are needed in all 
land giants to counter compressive loads or not. If not, then leg posture in 
giants is selected for or against not by mass issues, but speed performance. 
For instance we humans have straight knees despite not being gigantic - we are 
slow. Ergo, Bonnan's link between the factors is not correct, a common error he 
shares with a wide variety of researchers. 

In my last post I noted that Bonnan's opinion is that titanosaur arms may 
have been flexed (which again raises the issue of why other sauropods would 
have 
straight limbs to support mass, could use some consistency here). Bonnan took 
umbrage at this. Why? It IS his opinion that titanosaur may have been flexed. 
No criticism was stated or implied or offense intended, it was a simple 
observation on his opinion. It is, for my example, my opinion that titanosaur 
arms 
were not flexed (for reasons will not go into here).
   
Bonnan said about scapula orientation -
"Define subhorizontal, because you and I are talking past each other.  30-45 
degrees IS subhorizontal to me, as opposed to say 90 degrees or more which 
is what is seen in some other reptiles as you say.  And, again as stated in 
my paper, I angled the scapular blade at approximately 40 degrees from 
horizonal, aka, subhorizontal."

Here is how it works. Vertical is 90 degrees or close to it. Subvertical is 
between that and 45 degrees. 45 degrees is not as Bonnan states subhorizontal 
because it is exactly in between vertical and horizontal. Subhorizontal is 
between 45 degrees and horizontal, which is 0 degrees or close to it. There is 
absolutely no evidence that sauropods had vertical scapulas and the few 
restorations that show them so are grossly incorrect. I always show sauropod 
scapula as 
subvertical as they protract and retract. The most retracted position I 
restore is compatible with Steven's last SVP posture as I recall, which was not 
truly subhorizontal despite what the abstract said. In Bonnan's Fig. 9B showing 
his prefered sauropod arm posture the scapula is at about 25 degrees (not 40 as 
he claims), which is approaching horizonatal and much lower than restored by 
Stevens. Wilhite's scapula  posture is similarly errant. Since there is no 
ostelogical justification for subhorizontal or horizontal scapulas in any 
sauropod, since such scapula-coracoid posture requires an aberrant subvertical 
anterior sternal complex, and since such postures are limited to nonwalkers 
like 
fliers and diggers, there is no good reason to restore them that way. 

When I saw Wilhite's presentation at last SVP I was appalled. Silly me, I 
have standards and criteria that expect research to produce results that make 
some sense. Sauropods with avian posture scapulas and elbows flexed contrary to 
the osteology do not. Wilhite's work is by no means excellent since he failed 
to provide sufficient reason for his model's peculiarities. Hopefully Wilhite's 
work will improve in the future, either by corrections, or providing 
compelling evidence for his results. 

In my last post I said -
"The basic posture of the scapula is not directly dependent on the existence
or nonexistence of shoulder girdle mobility, since the scapula is 
subvertical whether or not it can move in walking tetrapods."

To which Bonnan asked -
"Greg, when I have said this?  I brought up shoulder motion in my paper 
simply to address that it might occur but that it would not effect the 
conclusions of my study, which were about manus orientation and shape, _not_ 
sauropod locomotion per se."

Bonnan said what I said in his 2nd to last post -
"Greg, that doesn't follow, unless you're basing the sternal thing on 
chameleons or other lizards.  You bounce back and forth between lizard and 
mammalian models for the scapulacoracoid movements and positions in your own 
work, but neither of these have to be the only models for dinosaur 
scapulocoracoid movement (or non-movement).  Birds, which are direct 
dinosaur descendants, certainly don't have such a gliding articulation with 
the sternum, and crocodylians don't either, so far as I know.  We have such 
little data on sauropod (or other dinosaur) sternals that to postulate a 
cartilaginous episternum in which the coracoid traveled in is stretching it 
a bit.  Maybe, but maybe not.  I can imagine all sorts of possible sternal 
articulations and scapcoracoid movements, but just because they seem logical 
doesn't mean that was the actual mechanism."

It was Bonnan who brought the subject of scapular mobility up. To repeat what 
I said in the last post, scapula orientation in sauropods is not connected to 
their mobility or mobility, since scapulas are oriented vertically in land 
walkers regardless of shoulder girdle mobility. 

In his 2nd to last post Bonnan said - 
".... the more you tilt the shoulder blade in a sauropod 
up, the further posteriorly that glenoid is going to face.  And it gets to a 
point where the humerus would become horizontal because the humeral head of 
sauropods articulates up and back.  You cannot have a vertical 
scapulocoracoid and a vertical humerus.  I noticed this, Ray Wilhite has 
noticed this, and Phil Platt noticed this, all of us independently.   Again, 
look at the figures in my paper and read the descriptions -- it is fairly 
evident that the only way a columnar limb would have worked in a sauropod is 
for that scapulocoracoid to have been sub-horizontal -- 30-40 degrees."

Nein. In flexed armed ceratopsians (of all sizes) the shoulder glenoid faces 
strongly posteriorly with the scapula subvertical, so the humerus is not 
vertical. When the scapulas of sauropods (and stegosaurs) are in the same 
position 
the glenoid faces much more ventrally, allowing the humerus to operate as a 
vertical element during the entire limb stroke. This is detailed in Fig. 4 in 
Paul & Christiansen Paleobio 2000. So quadrupedal dinosaurs did much the same 
thing as mammals - as the humerus became more vertical the orientation of the 
scapula blade remains the same, it is the shoulder joint that changes. So 
elephants have vertical scapulas like gazelles. Sauropods had the same scapula 
orientation as protoceratopsids - not surprising since they shared the same 
basic 
quadrupedal shoulder girdle arrangement, one dramtically different from birds 
and pterosaurs.

Bonnan asserts that I strongly crossed the radius-ulna of Brachiosaurus - 
which I too examined in (then East) Berlin - in my DPP paper. Take a look at 
fig 
3a. In anterior view I show part of the proximal ulna lateral to the radius. 
Distally the radius mostly overlaps the ulna, only a small portion of which is 
exposed lateral to the radius. The radius is only slightly crossed relative to 
the ulna, about the same amount as in Bonnan's fig 9B. 

Bonnan complains that I insulted his intelligence by repeating a quote of 
mine out of its obvious context. As I said in my post, there is no doubt that 
he 
has does not understand how horse wrists work. And, as also said next in the 
last post, nor does anyone else. That includes moi. I'm an equal opportunity 
critic. What I do object is Bonnan making assertions about horse wrist function 
that are based on speculation rather than direct observation. Such as "I have 
difficulty accepting that wrist mobility in horses literally involves massive 
disarticulation of the carpals." Well, what is the alternative since the joint 
articulations of horse wrists allow only limited rotation, no where near the 
observed extreme degree of wrist flexion horses regularly achieve? The carpals 
have to come apart to a radical degree, a disarticualtion hinted at in Ell
enberger's classic figure which shows a moderately flexed wrist (my statements 
not being inconsistent as Bonnan asserted). What I do not know is how horses do 
it. But since horses do disarticulate the wrist to flex it more than ~30 
degrees, it is very possible sauropods did the same in order to flex their 
hands 
beyond the articulations described in good detail by Bonnan. 

Bonnan suggests I do direct research on animal locomotion. By George he's 
right. So here's what I'm going to do. Will start with equine wrist action. 
Need 
money for the X-ray, etc. Do not have access to grant funds and the like. But 
that's no  problem. Upon returning from SVP will rob a bank - heck it's 
Baltimore and they don't need the cash anyway. With no institutional backing 
will 
figure out some way to get someone to provide needed horse et al. Should be 
easy 
enough. Or maybe not. Perhaps I should work on elephants. No doubt lots of 
zoos would loan me one for a few hours. Or maybe the circus. Not sure what to 
do 
with it without research finds but I'm an optimist. For those who argue that 
those without access to the means to do such research should avoid working in 
biomechanics I refer them to the title of a novel centered on the activities 
of a B-25 squadron in the Italian theatre circa late WW II.    

Since Bonnan says he will not reply, and as I'm departing for SVP via other 
stops along way, this will hopefully be my last post on this subject (can hear 
the cheers from here). Anyway have to get prepped to rob that bank. And find 
that horse. 

G Paul