sauropod arm articulations

[GSP1954@aol.com]

In the latest JVP Matt Bonnan restores the articulation of the arms of 
sauropods, with special emphasis on the elbow in which he argues that the 
radius is 
positioned more medially than normal. This got me curious so I got out the 
figure I published of the elbow articulation of Brachiosaurus in the Dinos Past 
7 
Present vol 2 back in 87. Lo and behold my articulation diagram is 
essentially identical to Bonnan's in fig 9B of Apatosaurus. I used the same 
articulation 
because the position of the olecranon process relative to the medial and 
lateral articulations of the ulna for the humerus forced it. Also because this 
pronated the hand as per Bonnan's observation. 

The main difference between the over all pose of the arms is that Bonnan 
rotates the entire arm along its long axis so the anterior surface faces more 
medially. This would seem to create problems in flexing the arm joints during 
the 
recovery stroke, but it fits the trackway evidence. 

Bonnan argues that sauropod wrists could flex significantly, but to a limited 
degree. I wonder about this because the horse wrist can flex only a few 
degrees with everything in proper articulation, but up to 120 degrees during 
the 
recovery stroke, and almost 180 when folded up while lying on the ground. 
Massive disarticulation of the carpals is involved. I suspect sauropod wrists 
could 
flex to nearly 90 degrees to clear the hand from the ground during the 
recovery stroke. 

All restorations showing the scapula-coracoid subhorizontal are grossly 
incorrect. In virtually all tetrapods the scapula is sub-vertical, vertical, or 
even  tilted forward. Rotating quadrupedal dinosaur scapula-coracoids to nearly 
horizontal forces the sternal complex to be nearly vertical, which is absurd 
since in tetrapods the sternum is subhorizontal. It is hardly likely that 
sauropods for some reason violated this basic pattern. Horizontal blades are 
found 
in flying archosaurs with strongly flexed coracoids (pterosaurs, birds and near 
avian theropods) that articulate with the front end of the horizontal 
sternum. 

Bonnan argues that sauropods had straight limbs because land giants have to 
in order to bear their mass in 1G. This is not correct because many land giants 
had flexed legs judging form their joint articulations - indricotheres (as 
correctly noted by Gregory and Granger back in the 30s), recent extinct giant 
rhinos and living rhinos, titanotheres (as detailed by Osborn in his classic 
titanomonograph), ceratopsids (Paul and Christiansen in Paloebiology), 
hadrosaurs, giant theropods (Paul in Gaia). Straight versus flexed is linked to 
running 
performance rather than sheer size. 

G Paul