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Re: Blood flow in Sauropods

In a message dated 95-09-10 04:14:52 EDT, pwillis@ozemail.com.au (Paul
Willis) writes:

>A 8 metre long neck, 3 metres above the ground allows you to cut a 16 metre
>wide swathe through the vegetation at a height of 3 metres of less without
>overloading the blood circulation to the head associated with raising the
>neck above the horizontal (of course these figures allow for maximum
>lateral movement of the neck, but you get my drift). That is a blinking
>good use for a long horizontal neck.

Right. But LOWERING the neck below the horizontal to the ground creates the
same kind of blood-pressure problem that raising it above the horizontal
does, namely, how to bring the blood back up from the head. In order not to
suffer blood-pressure problems, the head must be kept AT the level of the
heart, neither above nor below it. And there is still the problem of bringing
the blood back up from those 3-meter-tall legs. It seems indeed significant
that in many tall vertebrates (elephants are exceptional, but they have
trunks), part of their height comes from elongated legs, part from an
elongated neck--as if striving to keep the heart midway between the extremes.
Once the heart can generate enough blood pressure to get to the head "on
high," it can also generate enough blood pressure to bring blood back from
the legs below, and vice versa. This coincidentally dovetails nicely with the
requirement that animals on tall legs still need some means of reaching
ground level to drink, etc.