Re: Sauropod Energetics (Peristaltic pump)

[Sim Koning <simkoning@msn.com>]

> Would some sauropods need to maintain blood flow in order to raise their
> heads long enough to take a mouthful? Surely if a diplodocid (or other
> species that maintained horizontal necks most of the time) was able to
> seal off the blood supply out of the neck for a few seconds to prevent
> blood from draining away from the brain, then a few moments of no blood
> flow to that tiny brain wouldn't be so critical?

> It would mean they couldn't raise their heads for any length of time
> (barring other unknown blood flow mechanisms), but it wouldn't make
> quick forays into higher elevations entirely impossible.


That's Bakker's hypothesis, but I don't know how long even a small brain 
could function without a constant oxygen supply. It would mean that these 
animals would have to rear up, eat for a few minutes, go back down and 
repeat. Would this practice burn more calories than what it actually got 
from the tree? It makes me wonder if this "working out while eating" 
strategy would be worth it.


> One problem with the peristaltic idea is that this type of muscular
> contraction is restricted to the digestive tract in vertebrates

Peristalsis is also used for oviducts, ureters and other tube-like organs.

> and nothing like it is known for the vascular system for any extant
> vertebrate. One would have to postulate that sauropods evolved a
> structure not known to occur in any living animal


Annelids (worms) use peristalsis to pump blood through their circulatory 
system. This type of system is the most primitive form of closed circulation 
and was probably the system that the ancestors of all vertebrates used 
before developing a centralized heart. It should also be noted that the 
arterial walls still retain muscle tissue and that the heart was probably 
derived from earlier peristaltic systems.
Sauropods, in my opinion, could have easily evolved such simple system 
again.


> An additional
> problem is that this idea isn't testable.

Neither is the notion that they had a giraffe like system

>As I'd noted in another
> post, if Kent's reconstructions are correct, cardiovascular
> adaptations seen in living mammals and birds would work quite well in
> sauropods, without the need to postulate mechanisms for which there
> are no known extant examples... :-)

It still doesn't explain how sauropods could rear straight up and not lose 
consciousness. With all the examples I've given, I don't understand why this 
is being taken as such a far fetched idea.


> The last point (#5) is a bone of contention. Some silhouette drawings  
> suggest sauropod necks >that naturally curve upwards, but under  scrutiny, 
> those silhouette drawings show subtle-but->cumulative  geometric 
> inaccuracies, and anyway, apparently at least some such  illustrations are 
> not >even intended to depict the ONP.

Kent, While I agree the the ONP was probably horizontal with most, if not 
all sauropods, is there any way to reliably put a limit on their 
flexibility? Human contortionists can bend their spine to an incredible 
degree without any ill effects, is it possible sauropods could do the same 
with their necks in some cases? I also think sauropods are much more 
analogous with elephants. I've always viewed the long neck as serving the 
same function as the trunk of an elephant, an organ that allows sauropods to 
browse low and high with equal efficiency.

_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today - it's FREE! 
http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/