sauropod rearing

[Kendall Clements <k.clements@auckland.ac.nz>]

Re: Sauropod rearing

I've been really interested by this thread. Some terrific biomechanical 
work has been done in this area. I have the Discover article but have 
not yet seen the new Science paper. I look forward to that. I have two 
comments.

1. I'm damned if I can remember where, but I read that modelling blood 
flow to the head is not simply a matter of estimating the pressure of 
the column of blood in the neck above the heart. Since the vascular 
system is to a certain extent closed, the venous return could have 
acted like a siphon if the walls of the veins were more rigid than 
usual (the walls of veins are usually fairly flexible, which is why 
veins can collapse). Blood vessels in the neck of sauropods could have 
been tightly encased in connective tissue, preventing (a) outpocketing 
due to local pressure increases, and (b) collapse due to local pressure 
decreases. As a result, the heart would have been aided by the pull of 
the venous return. As I said, this is NOT an original idea, and it is 
not an alternative to multiple hearts and/or arterial valves. I'd be 
interested to hear the views of some of our medically-orientated 
subscribers on this! Is it possible? One problem is that if the walls 
of neck veins were relatively rigid, and blood pressure dropped beyond 
the point where it could be compensated by siphoning, outgassing would 
occur and the dinosaur would have a rapid and fatal coronary embolism.

2. While I like the idea of modelling sauropod anatomy and physiology 
based on the laws of physics, I'm not so keen on reasoning along the 
lines of "they had long necks therefore they must have fed in the 
trees." Gould and Lewontin addressed this issue a long time ago (Gould, 
S.J., and R.C. Lewontin.  1979  The spandrels of San Marco and the 
Panglossian paradigm: a critique of the adaptationist programme.  Proc. 
Roy. Soc. Lond. B 205: 581-598). Sauropod necks came in a great range 
of shapes and sizes (compare Dicraeosaurus with Mamenchisaurus), and 
the ratios of forelimb length to hindlimb length varied considerably. 
Ascribing function in the absence of a comparative (phylogenetic) 
framework is a dangerous business.

Kendall

----------------------
Kendall Clements
k.clements@auckland.ac.nz