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RE: MAMENCHISAUR NECKS
I certainly agree about long necks being ideal for high foraging. But
I'm not sure grazing should be ruled out.
I'm prone to think the "long necks" did a bit of both. It all comes down
to the debate on energy.
Because of huge necks like found with _Diplodocus_ and _Mamenchisaur_,
many have suggested that grazing was a more common method of eating.
The big issue here (or one of them) is blood pressure. Myself, new to
forums such as this news group has never been privy to such discussions
on this subject, but I've heard its a hot debate topic. Apparently, the
amount of energy needed to keep the head and enormous neck aloft on one
of these giants, would have caused tremendous strain on the heart. And
wouldn't they be deprived of oxygen feasibly?
On the other hand, what if they had a superior cardiovascular system,
and networking that blood from the heart to the head was done more
efficiently than what has been suggested? Perhaps they had somewhat of
an auxiliary supply of blood up by their head ready to process if
certain arteries collapsed from blood pressure during extended bouts of
vertical feeding. The latter, to me sounds a little extraordinary, but
it has been suggested. One solution, I heard, was a suggestion that some
of the "lengthier in neck" sauropods had 3 or 4 gigantic hearts. Again,
I'm not saying I subscribe to this one either.
What do people think? Has anyone heard any new developments in this
debate? I'm not sure where I stand on it, myself. Perhaps, they only
raised their heads high or stood on their hind legs (again, another
debate on standing) only for short times. Perhaps only to tear down a
branch to eat it on a lower elevation.
Is there even a "going" accepted or popular standpoint on this?
Sent: Wednesday, July 22, 1998 10:52 AM
Subject: Re: MAMENCHISAUR NECKS
Brain is quite correct. Evolving a hyper-long neck just to low
maladaptive in evolutionary and energetic terms. A very long
neck requires a
correspondingly long trachea. The latter dramatically increases
respiratory dead space, inceasing the energy needed to breath.
So evolving a
long neck in order to save foraging energy actually ends up
energy budget. Add to that the energy needed to grow such a long
high browsing explains such extraordinary necks.
As for Mamenchisaurus, the articulated skeleton in the ground
the neck kinked strongly upwards at its base, as in Euhelopus
Camarasaurus. So it was carried erect, not horizontal. The arms
fairly long too. Mamenchisaurus was giraffe-like, not low slung.