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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?

Jamie Close

        ----------
        From:  GSP1954@aol.com[SMTP:GSP1954@aol.com]
        Sent:  Wednesday, July 22, 1998 10:52 AM
        To:  franczak@ntplx.net
        Cc:  dinosaur@usc.edu
        Subject:  Re:  MAMENCHISAUR NECKS

        Brain is quite correct. Evolving a hyper-long neck just to low
browse is
        maladaptive in evolutionary and energetic terms. A very long
neck requires a
        correspondingly long trachea. The latter dramatically increases
the
        respiratory dead space, inceasing the energy needed to breath.
So evolving a
        long neck in order to save foraging energy actually ends up
increasing the
        energy budget. Add to that the energy needed to grow such a long
neck. Only
        high browsing explains such extraordinary necks. 

        As for Mamenchisaurus, the articulated skeleton in the ground
clearly showed
        the neck kinked strongly upwards at its base, as in Euhelopus
and
        Camarasaurus. So it was carried erect, not horizontal. The arms
were probably
        fairly long too. Mamenchisaurus was giraffe-like, not low slung.


        GSPaul