Re: sauropod arm articulations

[GSP1954@aol.com]

Yikes, it would be nice if folks actually read and responded to what I've 
written and illustrated. 

Contrary to Bonnan's implications, I never implied that sauropod's did not 
have straight limbs, as anyone who is familiar with my research and 
illustrations of 25 years knows. I've always emphasized the elephantine posture 
of 
sauropod legs. In responding to Bonnan's implication in the JVP paper that 
sauropods 
and all land giants must have straight legs, I noted that joint morphology as 
well as limb proportions show that many giants had or have flexed legs 
suitable for true running with all feet of the ground. Sauropod legs were not 
straight because they were gigantic, but because they were slow. Sauropods, 
like 
elephants, could not achieve a full run, and probably could not exceed an 
elephantine 15 mph, which is a very low top speed. 

Bonnan claims that in the 87 DPP paper I strongly crossed the radius and ulna 
of Brachiosaurus. Not so, as seen in Fig 3, in fact I show the same partial 
cross over as in Bonnan's Fig 9 of Apatosaurus. The brachiosaur lower arm 
articulations are based on the excellent Berlin material and are correct, and 
pretty much the same as Bonnan's results. And his and my elbow articulations 
are 
the same. 

Last year I noticed the SVP abstract on supposedly horizontal scapulas in 
sauropods and went to the presentation to see what was up, or not. The scapula 
pose actually shown was 45% above horizontal, the maximum protracted position 
of 
sauropod scapulas, and therefore within the acceptable range and not at all 
subhorizontal. Left me wondering what all the fuss was about. The scapula was 
positioned much more vertially than in Wilhite's not excellent motion studies 
of sauropod arms, which actually shows the elbows flexed! Which they certainly 
were not for the reasons described by myself, and Christiansen, as well as 
Bonnan (except possibly for titanosaurs in latter's opinion). 

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. Bonnan suggests that sauropods 
are somehow different so maybe their scapula posture was different from other 
tetrapods. This has no testable content. There is no logical reason why 
sauropods would have horizontal scapulas and subvertical sternal elements when 
other walking quadrupeds of widely varying postures, speeds and sizes have 
subvertical blades and horizontal sterna, and horizontal scapulas are only 
found in 
specialized nonwalkers such as diggers and fliers. The sauropod shoulder 
glenoid is directed strongly ventrally when the scapula is subvertical, if the 
blade 
is horizontal then the glenoid faces much more anteriorly than in required 
even for a vertical armed animal (see the comparative glenoid articulation 
diagrams in the Paleobiology paper Christiansen and I did). It is true that as 
one 
contributer observed that the scapula of hadrosaurs parallels the anterior 
dorsal series. The anterior dorsals of hadrosaurs follow a subvertical arc, and 
the scapula in likewise subvertical. It is just a coincidence due to the 
unusual pitch of hadrosaur shoulders. In sauropods the anterior dorsals vary 
from 
sloping down and forwards and up and forwards, scapula posture was independent. 

Bonnan said things about horse wrists that shows he does not understand how 
they work. Nor does anyone else. A chronic problem with the supposed science of 
paleobiomechanics is that people are doing lots of analysis and coming to 
lots of conclusions about fossil taxa without out first doing basic research to 
see what is actually going on in living animals, work that should have been 
done long ago. The partial disarticulation of equine wrist carpals is figured 
in 
Ellenberger's classic study of the anatomy of the horse, they obviously have 
to disarticulate an extreme amount as the wrist flexes 120 to nearly 180 
degrees. Someone is going to have to do x-rays to see exactly what is going on. 

G Paul