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RE: Dinosaurs are not mammals (last time for me)

Tracy Ford wrote:

>Muscles need area's to attach to, right? IF the jaw muscles attached to 
>the frill like you say, on the frill, around the fenestra, there is a 
>BIG problem. The middle of the muscle has to attach to something but 
>there is a hole, there is NOTHING there to attach to. It wouldn't work.

I know I'm probably going to regret wading in to this one, but I see it is
getting time for some information from the real world. I did both my
Master's and Doctoral theses, in part, on bird anatomy, and I can tell you
that it is simply not true that muscles can only attach to bone, or that
large fenestrae in bones cannot serve as the origin points of muscles. In
fact, there is a very good argument for suggesting that that is exactly
what they might be for, and I have long thought that the fenestrae in
ceratopsian frills must have served for some sort of muscle attachment.
Muscles consist of fibers and connective tissue, among other things, and as
long as there is connective tissue available the fibers themselves do not
have to arise from bone. Thus, it is not at all unusual for a muscle,
including the larger jaw muscles in birds, to have a very small area of
origin on the skull, but have large tendons or aponeuroses arising from
this area of origin that in turn provide origin for a large number of
muscle fibres, sometimes even several layers of them in overlapping
sequence. This mechanism, among other things, permits very large muscles to
take origin without requiring large areas of heavy bone to support them.
Therefore I would have expected in life that the fenestrae on the frill of
ceratopsians were covered by connective tissue which provided origin for
muscle fibers. If there were fibers originating from both side of this
connective tissue, so that the fenestra was covered with muscle tissue both
on the front and the back of the frill, it would be a perfectly normal
thing, as it became advantageous for the bone to become lighter, for the
bone to grow thinner between the two muscles until it was replaced by a
sheet of connective tissue that served as the origin for the muscle fibers.
Of course, I cannot prove that is was the case, but to suggest that the
fenestrae are evidence against muscles having risen from this part of the
skull is simply anatomically incorrect. 

>IF they had their jaw muscles attached to the back of the frill, that 
>would be a very volnerable, and an easy target to attack.

You are assuming that when someone says that muscles take their origin from
the frill, that they are saying that the entire frill must have served as
an attachment point for masses of muscle fibers. This is not necessarily be
case, and I in fact would expect this to be most unlikely. If muscles did
arise from the frill, my suspicion would be that the poster edge of the
fenestra might well indicate their furthest extent. Thus, any muscles
arising from the underside of the fenestra would have passed directly
forward deep under the frill, and would not necessarily be vulnerable to
attack. Note that these fibers, on both sides of the frill, did not
necessarily have to be massive, because there are advantages to having long
fibers as well as to having many of them. It all depends on the jaw
mechanics. Therefore, the mass of muscle arising from the frill may
actually have been relatively small, but may well have been composed of
unusually long muscle fibers. 

In any case, I think it is most unwise to be quite so dogmatic when
discussing any aspect of something has different from any animal living
today as one of these dinosaurs. 

Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net