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Re: again: frill of Triceratops



At 09:10 AM 9/18/96 -0500, Aravind wrote:

>A lot seems to be said about the frills of ceratopsians but probably a 
>little evolutionary analysis would help. First of all I would like to 
>know if the belief that the pachycephalosaur skull margin ornamentation 
>and the ceratopsian frill are homologous is well established. Anyhow I

        Good question.  Why is it important to the question at hand?  Oh
wait, I see...

>assume that to be the case and believe that the frill evolved through a 
>process of reinforcement. Initially it evolved  due to sexual selection. 

        Seems like aving a rim of horns around the base of skull might also
have a defensive purpose.  I mean, horns are sexy (not gonna go there...),
but are they sexy enough to just spring up out of nowhere.  I would accept
that as at least plausable, but I'm just not convinced that it's better than
them developing for defense.  Occam's Razor.

>Subsequently it gave a an oppurtunity for jaw muscle attachment and again 
>it was reinforced by sexual selection.

        Note, the jaws already attatched there.  Still, this is interesting...

>[...]Possibly this occurred  many 
> times in evolution like the Austropithecus. robustus cranial crest. I 

        The repeated pattern of sagittal crests is a feature of the great
apes.  The lack of this feature in humans is a reversal associated with
reduction in the need for heavy jaw musculature (gracile morphotype or
retention of juvenile gracility) or a concentration on other aspects of
human evolution.

>feel that in cicadelloids the ornamentation of thoracic segment 3 also 
>arose by such a process.

        Ya got me there, bub!

>So it is very possible that full use is made of 
>any new organ to do all possible things.

        I doubt all possible uses are realized.  Otherwise George Olshevsky
*would* have wings. :)

>                                   .    .
>                              .-_  /:\  /'\ .
>                             /'''\/:::\/'''/:\
>              
>                      STEGOSAURS WERE MEAT 

        Wagner
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| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
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