[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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