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Re: Running dinos

>   As if I haven't stirred up the mailing list enough....
>   For the last several days I've been trying to remember a lecture on
>evidence for dino speed.
>   There was some mention of muscle attachment points being a clue.
>Unfortunately, I can't remember what muscle attachment said about speed.
>   Where did theropod muscles attach (relative to hip socket) and why is
>this an indication of speed?

        Your more "typical" theropods -- that is, those without an
opisthopubic pelvis, like the dromaeosaurs and therizinosauroids -- have,
without getting technical, four muscles that attach the femur (upper leg
bone) to the pelvic (hip) region:  two in front of the femur, and two
behind.  The two in front serve to pull the leg forwards, the two in the
rear pull it back.  You can use a simple thought experiment, thinking about
what it's like when _you_ run, to get this picture:  the muscles in front
pull your leg forwards in the running stroke so you can plant it out in
front of you.  Then, the muscles in back take over and your body is moved
forwards over the leg.  Pretty simple, eh?  I'm not sure if anyone's done
any kind of research to determine if the "forward" or "backwards" stroke is
the more powerful in theropods...anyone?

        Anyway, in the opisthopubic dinosaurs -- the ones in which the
pelvis was turned backwards (the saurischians, at any rate) -- a muscle is
moved, too!  Thus, in these animals, there is only one muscle that pulls
the leg forwards, and _three_ that pull it back.  Imagine, again, that it's
_you_ running:  when you're pushing off (the "backwards" stroke)...that's
what launches you forwards.  The stronger the launch with each step, the
faster you're going to go (and the faster you'll acclerate, too)!  So it's
pretty easy to see why opisthopuby is an advantageous trait in a nice biped
like your average dromaeosaurid, and why it can affect speed.

        Since we're on the subject, and before anyone asks, I'm not
positive if the same holds true for ornithischian dinosaurs.  In the
opisthopubic saurischians, the pubis is large and broad (except,
apparently, in _Mononykus_) and serves well for muscle attachment, but in
ornithischians, the pubis is a skinny little rod, and doesn't have nearly
the necessary surface area for similar muscle attachment.  Does anyone have
any info on how this affects running in bipedal ornithischians?  Is Dave
Weishampel listening?  ;-)

Jerry D. Harris
Denver Museum of Natural History
2001 Colorado Blvd.
Denver, CO  80205
(303) 370-6403
Internet:  jdharris@teal.csn.net
CompuServe:  73132,3372

--)::)>   '''''''''''''/O\'''''''''''`  Jpq--   =o}\   w---^/^\^o

Overheard in the Denver Museum's
old Fossil Mammal Hall, from a mother
to her daugher:

"See there?  That's the camel-dinosaur, and
the horse-dinosaur, and the elephant-dinosaur..."

--)::)>   '''''''''''''/O\'''''''''''`  Jpq--   =o}\   w---^/^\^o