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Re: MAMENCHISAUR NECKS



Brian,

    I think you may have misinterpreted what I was suggesting.  My reference
was not to "ground-level" grazing, but referred to grazing on aquatic plants
while in water deeper than, say, the animal's rib cage.  In fact, it seems
certain that the specific gravity of the body of a living Mamenchisaurus was
less than that of either fresh water or sea water, and that the animal could
float, even if it didn't lower its body much below the surface.  In
floating, might the animal have used the long neck for grazing at depths
below the belly or maybe even deeper than the feet?

    Incidentally, in deep water the neck wouldn't necessarily have to bend
down deeply at its base, because the post-cervical body could might tilt,
and this could have been especially easy with that 19-vertebrae neck of
Manenchisaurus being as long as the rest of the body.

    By the way, moving a long, tapered neck of 19 vertebrae over any
practical degree of arc (especially with the vertebrae becoming smaller and
smaller), still requires far less energy than the moving of a body of
two-digit or three-digit tonnage!   Check the physics involved, Brian.
Whether grazing aquatic plants or terrestrial ones, the sauropod neck is
well adapted to reach vegetation in far narrower spaces than the main body
would have fitted into or through -- and I'm not referring to tree tops.

    Consider the possibility that there may have been stiff competition for
land plants as food, and aquatic grazing might have enhanced survival and,
thus, other life-process potentials.  I notice that the photo of a
re-assembled Mamenchisaurus skeleton on pages 36 and 37 of the book
referenced in my original post gives the impression (even considering that
there may have been some 'fish-eye' lens image distortion) that the animal's
cervicals taper remarkably toward the head,  possibly presenting the most
dramatic cervical-size gradation I've ever seen in any sauropod.  This taper
would conserve even more energy in moving the neck under water than it would
in open air (but this does not prove aquatic grazing, of course).

    You are, naturally, quite welcome to your opinion that, "Long
necks...evolved to reach high fodder, not graze", but this seems to me to be
a very GIRAFFE-BASED opinion, and it is disproved (as presented in your
post) by the marvelously long necks of certain marine reptiles!  They do not
use these to reach "high fodder", clearly.  But such necks were probably
useful in quickly snatching any prey within reach, and probably aided in
swimming as anyone with a rudimentary grasp of fluid dynamics can
appreciate.

    If you would like an off-list explanation of the ways in which long,
tapered necks can facilitate swimming, and -- especially --fast turns while
swimming, I may be able to take time for that; but  wouldn't want to expend
list space in doing so.  However,  I suspect you can figure that out for
yourself, if you wish.

    Finally, don't you find your opinion that long necks, "evolved to reach
high fodder" at least one step beyond that which current knowledge of
evolutionary mechanisms can realistically be said to tell us?

    Regardless of any difference in opinion we may have on this, I think
your dinosaur renderings of skin coloration and color-pattern distribution
may be closer to real than those of many artists.  Unfortunately, we'll
never know for sure unless a time machine becomes practical within our
lifetimes.  But to hear some theoretical physicists talk,  that may not
remain just Jules Verne's pipe dream.  I suspect there are some dino lovers
who would volunteer for an early, experimental run!

    Ray Stanford



From: Brian Franczak <franczak@ntplx.net>
To: dinosaur@usc.edu <dinosaur@usc.edu>
Date: Wednesday, July 22, 1998 9:25 AM
Subject: MAMENCHISAUR NECKS


>RAY D STANFORD wrote:
>
>> If the incredible neck was not an adaptation to 'grazing'  IN WATER-> -
conceivably even to swimming --  then I'd like to hear a better
>> explanation.
>
>I still fail to see how an incredibly long neck (particularly so in
>_Mamenchisaurus_) is necessary for ground-level "grazing". Could it
>possibly expend less energy to keep moving that ridiculous pipeline of
>neck around than it would to just take a few steps to reach new fodder?
>A grazer's neck only needs to be long enough to get the head down to
>ground level. Long necks, IMO, evolved to reach high fodder, not graze.
>And Ray, how does the long neck of _Mamenchisaurus_ serve as an
>adaptation to swimming?
>
>Brian (franczak@ntplx.net)
>http://www.paleolife-art.com