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relative size of animalsThe Problem of Pumping Blood to the Head of a Giant Dinosaur

There has been much discussion about how giant dinosaurs were able to pump blood to their brains. Let us start by comparing a giant apatosaur with a giraffe, an elephant, and man as shown in Fig. 9

Figure 9. Relative size of animals

 

Apatasaur

Giraffe

Elephant

Man

Weight

35 tons

1.5 tons

5 tons

75 kg

Neck length

12.5 m

2.5 m

?

a few cm

Heart size

?

12 kg

?

1.5 kg

Pumping rate of blood

?

10L/s

?

0.1 L/s

These numbers suggest that the dinosaur heart should not weigh more that one ton. However, Pedley [14], taking into account the blood flow rate and the fact that the blood has to be pumped 10 or more meters upward, suggests that the heart should weigh about 5 tons. Whether one ton or 5 tons, it would be a giant heart pumping blood up to a high pressure, somewhat like that of an automobile tire.

To overcome the problem of pumping blood to such heights paleontologists have all sorts of suggestions. First of all, Bakker [15] suggested that these giant creatures had to have more than one heart to be able to pump blood up the neck, see Fig. 10a. However, this represents a most unlikely physiology.

A second group, Seymour and Lillywhite [16], said that dinosaurs held their necks horizontal or sloping downward slightly. A complex computer model by Stevens and Parish [17] seems to indicate that the apatosaur, with its unusual bone structure and its 12.5 m long neck, would be unable to lift its head more than 3-4 m, thus lending weight to this idea. Figure 10b shows the horizontal-necked dinosaur.

Other creative life scientists, Seymour et al [18] calling upon their imaginations, came up with still another idea; that dinosaur hearts were located, not in their chests, but up in their necks. This is shown in Fig. 10c.

Proposed explanations

Figure 10. Proposed Explanations
a) Dinosaurs with multiple hearts [15].
b) Horizontal necked dinosuars who cannot raise their heads [17].
c) Dinosuars with their hearts near their heads. This requires that the lungs be near the heart, but I do not know how to show this in the figure [18].

 

The Siphon Explanation

Still another group of scientists proposed using siphons. Let us look at these devices. Figure 11 shows three situations, first where the siphon sucks fluid up from the heart and then returns it, secondly sideways and back, and finally downward and back up. The only power needed in these three arrangements is that required to overcome the frictional resistance of the flowing fluid.

Figure 11 (below) From the first law of thermodynamics the three flow systems in this figure all require the same pumping power.

three flow systemsHow high can a siphon work? Figure 12 shows that water can be sucked up about 10 m, minus about 1 m to account for frictional loss caused by fluid flow and by the vapor pressure of the water. So if a siphon tries to raise water more than about 8 m it won't work. Similarly, for blood with its different physical properties, a siphon can not raise blood more than about 7 m.

Tall Siphons

However, Seymour et al [18] overcame the tall-siphon difficulty by having the heart move up the neck, see Fig 10c. Seymour and Lillywhite [16] later came up with the idea of using partial siphon, see fig. 12c. This is just nonsense.
Choy and Altman [19] have an even more creativeplan - use hearts and valves at 2m intervals up the neck. Thus they propose that the Barosaurus has 8 hearts, two in the thorax, and three pairs in the neck, as shown by them and duplicated here in Fig 13. But fluid mechanics tells that this is pure fantasy.

water siphons

 

Figure 12.
(a) Water siphons less than about 9 m high will work [20].
(b) Above about 9 m will not work.
(c) Partial siphons have been proposed [16] but are just nonsense.

 

eight hearts

 

 

 

Figure 13. This design is clever but will not work. This figure is from Choy and Altman [19] .

Finally, by assuming a higher atmospheric pressure we have a physically reasonable explanation for how to operate a siphon taller than 7 m. Figure 14 shows that when the atmospheric pressure is roughly over 2 bar these long necked creatures could exist. Thus we tentatively conclude that the atmospheric pressure at the time of dinosaurs had to be higher than one bar or at least 2 bar.

At these higher atmospheric pressures taller siphons would work -
at 1 bar 7 m high; at 2 bar 14 m high, and so on.

tall siphons will work

 

 

 

 

Figure 14. With a higher atmospheric pressure taller siphons will work.

 
 
 
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