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Re: Amargasaurus



Matthew Bonnan writes,

>And went on further to say that the humps were potentially fatty and stored 
>energy, etc., like bison (and camels I presume).  The reference does not 
>come immediately to mind, but it was published in the journal of 
>paleontology if I recall correctly.  My problem with this idea was that the 
>large neural spines of a bison are supporting large muscles and the nuchal 
>ligament for their big heads.  Camels, which have very large humps, do not 
>have very large neural spines.  Can we infer a fatty hump from tall neural 
>spines?  What's up with spinosaurs, then, or for that matter Dimetrodon and 
>other pelycosaurs?  

Since I had the opportunity to hear this idea presented at a professional 
meeting, with slides and all, perhaps I can shed some light:

The basic problem with the sail reconstructions in spinosaurs/ouranosaurs has 
to do with the morphology of those "spines."  In these two dinosaurs, the 
neural processes are shaped like a canoe paddle: flat and blade like.  In the 
presentation, the speaker showed that the neural processes are similar in 
morphology to the processes found in both modern and fossil pigs, both of whom 
do not possess a sail.  In these two cenezoic mammals, the blade-like processes 
result in a hump structure.  Naturally, since pigs have heavy heads that are 
often used to root out tubers, the hump was probably the attachment site for 
the neck and head muscles; this gave the head more strength and stability.  
Yet, the muscle-attachment idea appears applicable to animals that have long 
processes; in animals that posess smaller ones, fat deposits are inferred.

In Dimetrodon, the neural processes are shaped like a fencing foil: long and 
thin.  Just as in fish fins, or the frilled lizard's frill, long and thin 
structures are good for supporting thin membrane-like structures.

Still questions remain.  If spinosaurs had a hump for muscle attachment, what 
was the purpose?  Why would two separate species need an entire bodylength of 
lengthened processes?  I assume that since both spinosaurs and ouranosaurs had 
humps, they lived in identical environmental conditions.  To make things more 
interesting, if these two had a bodylength hump, would that force them to be 
quadrapeds???

Of course, due to the fragmentary nature of the spinosaurus material, it is 
hard to make any solid inferences.

Hope that helps.


Rob Meyerson

***
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