Blood pressure in Sauropoda

[StephanPickering@cs.com]

       Probably the best investigation is that of Roger S. Seymour and Harvey B. Lillywhite, 2000. "Hearts, neck posture, and metabolic intensity of sauropod dinosaurs", Proceedings of the Royal Society of London 267B:1883-1887. This finally puts to rest the arguments of Choy/Altman that sauropods possessed multiple hearts: the intermediate evolutionary stages for a fully functional heart would serve no purpose. Another investigation is that of H.S. Badeer and J.W. Hicks, 1996. "Circulation to the head of Barosaurus revisited: theoretical considerations", Comparative Biochemistry & Physiology A114:197-203. Also of interest is: Andreas Christian & Wolf-Dieter Heinrich, 1998. "The neck posture of Brachiosaurus brancai", Mitteilungen aus dem Museum fur Naturkunde zu Berlin Geowissenschaftenliche Reihe 1:73-80. 
        Most sauropods held their necks in a horizontal  position, except for the brachiosaurs with their vertical necks -- and it is this taxon which is in need of further anatomical deductions. A giraffe, for example, has blood nearly 5 times thicker than animals of comparable size in order to produce a blood pressure nearly twice that of extant mammals (A.H. Rossof in 1972 published "An electrocardiographic study of the giraffe", American Heart Journal 83(1):142-143, which is most interesting).  One can, as Roger Seymour estimates, postulate a sauropod with blood pressure 7 times that of the giraffe, a heart 15 times thicker. To be explained, to be sure, is how the brachiosaur maintained hydrostatic pressures. Perhaps, like the giraffe, their necks' vascular system consisted of rete mirabile to prevent blackouts when they spread their forelimbs and lowered their heads to drink. Moreover, it is likely the brachiosaurs!
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ossessed strong back musculature and ligaments to sustain the neck in a gentle S-like curve so as to feed on foliage (like the giraffe) not accessible to other taxa. A giraffe of about 800 kg has a blood pressure of 353/303 mmHg, a blood volume of 73-78 ml/kg body weight, a 12 kg heart (with a left ventricle 7.5 cm), and a pressure at the base of the brain of 200mmHg. A giraffe, like a brachiosaur, never has a neck at a perfectly vertical angle, being at an angle of about 44.67 degrees.
       Also to be considered is that the known chest area of well-preserved skeletons has a discernable area constraints on how large a heart an animal could possess to produce necessary blood pressures to supply the sauropod's brain with blood and oxygen. No known articulated cervical series shows evidence of scarring from the ancillary heart pumps theorized by Choy/Altman, and as yet unexplained to my satisfaction is how the tracheal "dead space" in the neck was overpowered, as it were, by the respiratory system's musculature. The brachiosaurs, thus,  were able to live with necks and heads higher than other sauropods...somehow, they had a physiology balancing pressure gradients, blood densities, flow velocity/direction, and blood viscosity (the Navier-Stokes Equation might prove an avenue of research into brachiosaur physiology).  The giraffes have seemingly collapsible jugular veins, so that when the head is raised the hydrostat!
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 (gravitational) pressure is increased, the heart perfusing the brain with blood.