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Re: IDEA CONCERNING THE CAUDOFEMORALIS MUSCLE AND THE RUNNING ABILITY OF DINOSAURS




On Wed, 21 May 1997 Tetanurae@aol.com wrote:

> Here's an idea that's been running through my head.  It is often claimed that
> dinosaurs had sub-standard running abilities comared to mammals and birds
> because they had disproportionately short metatarsals, but a thought occured
> to me.  Perhaps the unusually long metatarsals of modern birds and mammals
> are an evolutionary response to the reduction of the primitively huge
> caudofemoralis muscle seen in dinos and therapsids.

        Well, we still have to take into account the pterosaurs who
as far as I can tell never
did evolve the gracile metatarsus, yet they had elinated the 4th
trochanter and most of their caudal transverse processes- so they had
little in the way of CFL most likely. And it seems to me that mammals have
a heck of a lot of femoral arc even so.  
        I do think the knee-based mechanism is a likely explanation for
the long avian metatarsus.
What may be part of the explanation is found in Gill's _Ornithology_ -= if
you are a bird and want to sit down, and you can't move your femur much,
your tibiotarsus and tarsometatarsus had best be the same length- other
wise, as you try to sit down your center of gravity is either going to be
ahead of you or  behind you depending on how long the elements are to each
other. Similar lengths of the two let a bird extend or
retract a leg and keep its center of gravity in the same place. 
        I agree with you that it might be tricky to try and compare
dinosaurs and birds by the same standards when their legs are built so
differently. 
        On that note though, can we really compare Allosaurus and T. rex
limb elements, though, if one has (as Gatesy suggests for the
ornithomimids) an incipient knee-based retraction mechanism? Doesn't T.
rex have much the same kind of tail structure as an ornithomimid, reduced
fourth trochanter, etc? does that gracile metatarsus really tell us that
these things were speed demons, or that they were using more
knee-retraction and less femoral retraction? Anybody have anything to say
against our devil's advocate who says T. rex was a slow plodder (the devil's
advocate indeed!) and just had a long metatarsus to make up for a smaller
femoral arc? 
        Here's a question- if the avian center of gravity is roughly at
the knees when the animal is on the ground, what about during flight? I
would assume that you would want it at the shoulders. Does extension of
the neck forward move it up to the shoulders? 

        Nick L.