[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
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
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.