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RE: Mammals are not dinosaurs



Nick Longrich writes;

>        An obvious possibility is that the frill was a display 
>structure, and that evolving a couple of big holes in the thing lightened 
>the head, reducing both weight and excess bone tissue. The fenestrae 
>could just be covered over with skin. Simply economy.

Economic sure, but still unlikely.  The bottom part of the fenestra
has a hollow that leads directly to the lower jaw.  The only
reasonable explanation for this is that there was a muscle that
occupied that space.

Any display function was probably a secondary benefit.

>        Also, your explanation fails to account for the 
> *absence* of said fenestra in Triceratops. If they were there for 
>chewing, how could Triceratops just eliminate them?  If, however, they 
>were there only for decoration, a little selective pressure from highly 
>combative members of the same species, or the bone-crushing ability of T. 
>rex, might well select against fenestra and for heavy armor.

For the trike, it would be a trade off: trade chewing power for
defence.  The jaw muscles on the trike do end in a hollowed area,
tucked within the frill, which would help the animal tackle tough
vegetation (if it prefered it that way).

If these critters were as ornery as some have suggested, being
tempermental about any intruder regardless of species, then having the
jaw muscles unprotected would be foolish.  Especially since punctured
muscle is no fun to chew with.

>        If you don't buy the neck armor thing, take a look at one of the 
>Mongolian ankylosaurs. The damn thing has reduced its eight plates of 
>neck armor down to two *massive*, fused bone collars. Perhaps T. rex and 
>bataar did, so to speak, go for the jugular. 

This may be effective for the trike and the pachyrhinosaurines, but
not for the chasmosaurines.  The bone portion of the frill looks
rather flimsy to me, seeming like Rex could've crunched through with
little difficulty.  A weak defence at best.

Rob Meyerson
Orphan Vertebrate Paleontologist

***
"Great, he's even sounding like a Vorlon."
        -S.I.