I also can't imagine how that long neck evolved (and stayed there) without a huge competing advantage. The and usual advantage of large necks is feeding high, so I distrust the claim that an animal with a long neck couldn't keep his head up.
Unfortunately, that cannot work. All the capillaries in the head and brain would also need to be rigid, and strong enough to hold back that much suction. There's no way around actually doing the work to pump the blood up there, and letting it drain back down.
But that isn't a slam-dunk for extreme blood pressure. We have plenty of examples of valves in veins to help get blood back from lower extremities. A little musculature around a pair of such valves on an artery could easily develop into a secondary heart, and a series of them could eliminate much of the need for the actual heart to supply all the pressure, or for the aorta to resist it.
It is not unreasonable to expect to find novel adaptations in an extreme body plan. Supporting the idea in the absence of fossil evidence is hard, even when such a novelty would eliminate the need for such a novelty as absurdly high blood pressure. Biologists resist suggestion of soft -tissue novelties much more than suggestion of physico- mechanical absurdities because they are, after all, biologists, not engineers.
Yes, that would require all capillary vases to support 1 extra atm of pressure against the air, what is a large issue. But it does not require rigidity.
No, blood does not get pumped in your head with just movement. You don't swing your head below your heart to replace blood in your brain. Somehow the blood needs to be replaced with fresh oxygenated blood.
> I also can't imagine how that long neck evolved (and stayed there) without a huge competing advantage. The and usual advantage of large necks is feeding high, so I distrust the claim that an animal with a long neck couldn't keep his head up.
It is common consensus that Giraffe necks did not evolve just under competitive advantage, and the best proof for that is the fact that their necks are much much longer than any other species. If it was only competitive advantage, other species would have displayed similar trends. Sexual selection is a more likely explanation.
https://www.scienceabc.com/nature/animals/why-giraffes-have-...
I am no biologist (or physicist) but if a bulk(¿) liquid moves against gravity, then surely it needs assistance?
Getting the blood in a vessel to "just move" if that vessel leads many meters up, has got to be more difficult than if it weren't.
¿ I know capillary effects exist, and plants don't exactly get water up themselves by magic but ...
You just wrinkled my brain. Is there an actual group of fighter pilots without legs who are taking advantage of this?
The other thought about legless pilots is the feet I think are used for the rudder control (pedals), so there is some loss of ability to control without using your feet. While I think computers could probably take this over, in the end it does mean two less things to interact with the plane.
If that were the case, G forces wouldn't make people black out. https://en.wikipedia.org/wiki/G-LOC
It's not really obvious to me why the sauropod heart->head->heart loop shouldn't be considered as a "siphon". For all the blood that's going up there should be an equal amount of blood going down.
Because blood vessels are flexible. Siphoning would be disastrous for the body - capillaries would snap shut under the suction and we'd die.