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Re: MAMENCHISAUR NECKS



Just a brief sidebar to this discussion about the potential uses of the long
necks of sauropods:  Just last week there were postings about whether or not
large sauropods could lie down on their sides, and how could they get back
up.

    After some pondering (while scrambling to meet deadlines on my current
assignment, and other personal matters), I had this particular thought:
Maybe the long necks and tails were used to help the sauropods get
themselves up off the ground to a standing position!  (Perhaps Nathan could
run a variant of his sauropod tail program to see if the tail and neck could
generate sufficient torque and momentum to allow a 30+ ton sauropod to help
get itself up from lying on its side to a standing position).  The image of
an elephant rolling itself back and forth a few times to get just the right
amount of energy until it can flip itself into a more upright position was
the basis for this idea.  It might explain the size and shape of some of
these animals' necks and tails - at least a little.

    Comments?


    Allan Edels


-----Original Message-----
From: Brian Franczak <franczak@ntplx.net>
To: RAY D STANFORD <STARSONG@prodigy.net>
Cc: dinosaur@usc.edu <dinosaur@usc.edu>
Date: Wednesday, July 22, 1998 5:04 PM
Subject: Re: MAMENCHISAUR NECKS


>RAY D STANFORD wrote:
>
>> 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?
>
>I won't dispute the *possibility* of this scenario, but I find it highly
>contrived. Sauropods are terrestrial animals; why go through the
>elaborate rigamarole to feed this way?
>
>> 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!
>
>"Three-digit tonnage"? I think you've *seriously* overestimated the
>weight of sauropods. _Argentinosaurus_ is the only known sauropod that
>*might* fall into that category, but only Don Lessem thinks it weighed
>in excess of 100 tons. _Mamenchisaurus_ was a moderate-sized sauropod,
>certainly less than 50 tons. And don't discount the weight of that 30+
>foot neck. Anteriorly-tapering cervical vertebrae or no, that neck still
>weighed a significant amount.
>
>> 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.
>
>Actually, I don't think it's any more "dramatic" than in other
>sauropods, and to my eye, _Apatosaurus_ seems to have a much more
>noticeable "taper" nearing the skull.
>
>> 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.
>
>I fail to see how this is a useful analogy. Giraffes are terrestrial
>plant-eaters. Plesiosaurs are aquatic predators that have to actively
>*pursue* their prey. Of course the necks of plesiosaurs are "useful in
>quickly snatching any prey within reach". A sauropod neck does not need
>to function in this manner.
>
>> 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.
>
>While I have no doubt that sauropods could swim, I do not believe that
>they were particularly adept swimmers capable of using their necks to
>make "fast turns while swimming". And why would they *have* to?
>
>> 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?
>
>Maybe so. But it still seems more reasonable than the rather fanciful
>scenario you've created. _Mamenchisaurus_ in particular aside for a
>moment, the Late Jurassic Morrison Formation is *full* of long-necked
>sauropods: _Diplodocus_, _Apatosaurus_, and _Barosaurus_ just to name a
>few. The Morrison is described as "seasonally dry" and "extremely arid
>at times" (Terrestrial Ecosystems through Time/1992), so where are the
>lakes/swamps deep enough for all these sauropods to go swimming in?
>
>Just a thought.
>
>Brian (franczak@ntplx.net)
>http://www.paleolife-art.com
>