Re: [Re: Sauropod Trunks]

[archosaur@usa.net]

> A better explanation which I read in another paper (again - apologies

> for lack of refences - it was part of the ectothermy-endothermy

> controversy that was raging some years back) is that the dome-like

> skulls on these creatures allowed blood to pool in that area and hence

> stop the brain from overheating, which would have bene a  real problem

> in endotherms of that size.

> 

> I later read something else that was interesting.

> 

> J.S.McIntosh writes

> "Additionally, sauropods may well have had a carotoid sinus that served

> a sa  reservoir of arterial blood to perfuse the brain when the caratoid

> arteries collapsed due to insufficient systolic pressure during high

> feeding"

> ch.16 - Sauropoda

> in Weishampel, Dodson, & Osmolska, eds, _The Dinosauria_, 1988,

> p.405

> 

> When I read the above it made me think that, assuming a gigantothermic

> rather than endothermic metabolism of adult sauropods, the reservoir of

> blood would be to supply oxygen to the brain during periods of anoxia

> when the neck was held erect.  (or the blood may well have served both

> purposes).

> 

> Anoxia must have been a  real problem for sauropods.   We know for

> example how difficult it is for a  giraffe to pump blood to it's head

> against the force of gravity.  How much more so for a  creature that

> could hold it's head so much higher?  This is a very good argument

> *against* Bob Bakker's & Greg Paul's giraffe-like barosaurs &

> mamenchosaurs.  Another argument against giraffe sauropods is that their

> cervical vertebrae could not have supported the muscles required to hold

> the neck up stiffly.

> 

> "No sauropod has elongated neural spines at the base of the neck which

> could provide leverage for epaxial muscles for sustained elevation of

> the neck in a  giraffe-like manner"

> J.S.McIntosh _Ibid_ p.404

> 

> More likely is that the neck was held out more or less horizontally in

> front of the body & would sweep over the vegetation, allowing the little

> head to browse.  Occaisonally the beast would rear it's neck up & grab

> leaves and branches from tree tops, & when that happened it would be

> impossible for the heart to pump oxygenated blood up to the brain.  In

> those instances the blood stored in the dome-like top of the head would

> provide oxygen for the short time required.

> 

> --

> Kewl!   :-)

> 

> M.Alan   Proteus   CyBeRrDeWd
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That's all well and good for animals like Camarasaurus and Apatasaurus, but
what about Brachiosaurus. Having it's neck held out more or less horizontally
just doesn't seem to make sense (not with those forelegs at least)

Also wouldn't a head that is held up like a giraffe put less strain on the
muscles since you wouldn't have all that weight sticking out way in front, or
is this where the small sauropod heads come in.

Again, I can understand the whole horizontal bit with animals that have long
tails like diplodocids and camarasaurids. Their tails having the tendons that
cantelever their necks and all, but what about Mamenchisaurus and Brachiosaurs
with their (comaratively) small tails. In cases like that, I could understand
the more erect position of the neck.

Archosaur J


http://members.tripod.com/~jurassosauridae/index.html

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