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Re: tucking (long)



Betty -

        Thanks for your lengthy but highly informative post on the folding
of the arms!  8-)

>     Bipeds go both ways in what their extra appendages do when moving
>     upright.
>
>     Humans DON"T tuck their arms while running, we use the swing of the
>     arm to counterweight the leg movements.  We move pretty fast and cover
>     a lot of ground as steady runners.  We are built to run or walk over
>     long distances.

        Presumably this is due to the lack of a counterbalancing tail.
However, Ken Carpenter has mounted the two specimens of _Coelophysis_ for
the Denver Museum's new displays running, but the arms are out and
~sort-of~ in a human-like, swinging arms for balance pose.  When I inquired
why he didn't tuck the arms in, he pretty much responded that humans don't
do it and somesuch.  One is just running; the smaller of the two is
actually reaching, so that one has more of an excuse.

>     Basilisk lizards run with their arms tucked straight doun at their
>     sides.  They only do bursts, and the arms are moved out of the way as
>     the "landing" of the lizard is usually abrupt and they need the front
>     legs ready to land on.

        Yah, I've seen this, but I have discounted it as a viable solution
to the dinosaur running solution mostly because the basilisks aren't
obligatory bipeds, and their limbs articulate differently than those of
dinosaurs -- the dinos _could_ do other things, so those possibilities have
to be considered.  With more avian-style limbs, the natural assumption is
that they were doing something avian, but there's always been something
about tucking the limbs all up that's bothered me...

>     Birds that fly as their major means of transportation tuck their arms,
>     their wings don't move from a given position while running.  (You can
>     tell by looking at the feather directions where the wings fold next to
>     the body-the imprint of the wing is a permanent growth-pattern.)
>     Birds that are trying to take off are excluded from this
>     discription.(they hold their arms out)

        It's especially easy to see this in roadrunners.

>       I believe that animals that are solely dependant on bipedal movement
>     will swing their arms in counterbalance as the final goal of their
>     evolution, as it is a great aid to distribution of weights and
>     balances during locomotion.  Monkeys and lemurs aren't totally
>     dependant on walking or running, as brachiating is their main form of
>     movement.  Birds that run are devolving the use of the wing entirely,
>     and would soon have vestigal remaints of arms (probably just for
>     display purposes).  Penguins swim and the wings are used for that.

        Oop -- better watch that!  You're going to get some people thinking
that the reduction in the forelimbs of many theropods (e.g. tyrannosaurids,
abelisaurids) was a move towards such vestigiality!  8-)  Which, of course,
it may well be...

>     Thus:
>     large bipedal/quadrapedal dinosaurs such as hadrosaurs which spend
>     some time on all fours grazing (on whatever), would tuck while running
>     on two legs.

        ...as opposed to Peter Galton's now-old picture of a hadrosaur
running bipedally with the arms all the way back, like the basilisk.  ICK!
Are they tucking simply to get the arms out of the way?  Having longer arms
that are used in quadrupedal locomotion would necessitate getting them out
of the way.

>     large therapods would probably run with arms up out of the way of
>     their feet, stiffly forwards, and in a position where their arms would
>     be out in an attack position (even stumpy T rex).  They probably
>     walked with their arms tucked under their bodies.  The size of the
>     arms in therapods tends to the vestigal sort of paradigm.
>
>     medium therapods and smaller therapods, ornithosaurs, coulesaurs,
>     hypsepholodons(sorry, I'm at work-no spelling check for names) all
>     quite probably swung their arms to counterbalance their weight.  The
>     arms were of a significant size to affect weight shifts, and evolution
>     would tend to aid a mechanism that aids in aiding movement.  The
>     shoulder girdles of the ornithosaurs wouldn't allow for much rotation
>     side to side, but plenty from front to back.  Great arm swinging
>     stuff.

        Ornithosaurs?  Are you getting back to the old term for the
pterosaurs, or did you mean ornithopods?  ;-)  But seriously, there are
many theropods whos arms are larger with respect to body size than some of
the hypsilophodontids.  Except at the wrist, where the maniraptorans had
some autapomorphic functions, aren't the arms pretty much similar to the
larger theropods with smaller limbs?  If so, I would guess that if the
overall movement is the same, then they probably behaved the same while
running.  Just a guess...



Jerry D. Harris
Schuler Museum of Paleontology
Southern Methodist University
jdharris@lust.isem.smu.edu
        (Compuserve:  73132,3372)

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Humorous Quote Is Forthcoming...

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