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Re: the reason I asked about maniraptor limbs



This week I was fortunate enough to witness a juvenile crow exploring
the tree it was born in.  Less fortunate for the crow, my presence
caused it to panic & lose concentration - falling halfway down the
length of the tree and catching itself with its wings spanning two
branches, legs peddling freely without purchase.  The adult crow,
unable to do the mammalian mouth carrying rescue, settled for making a
raucous noise at me instead.  The little bird (I suspect) grew tired
and took the only option left to him - plummeted like a stone to the
ground neck first.

Why am I bringing this up?  I'm not entirely sure - just trying to
vocalise out loud the issues relating to flight "growing on trees",
mostly to see if I understand them myself, but also because a ramble
shared is a ramble halved, so...

What was the difference between the way those two crows handled
themselves?  The adult was able to regulate the speed at which it
approached each branch and was able to do so with a more mature
spatial awareness of itself and its surroundings, plus improved
talon/eye coordination.  If a juvenile bird that has not yet mastered
its own aerodynamic abilities runs the risk of dying every time a
potential predator wanders past, what hope do creatures of the same
basic body plan, but with little or no aerodynamic abilities, have?
An adult maniraptor should not be as ungainly as a juvenile bird, and
less likely to take stupid risks.  This still leaves little saving
graces when things go wrong, and early climbing would go wrong unless
aerodynamic grace preceded climbing as a result of some other function
of ground running life (do please interject if I make a leap of
assumptions in saying this or indeed at any other point during my
ramble).  One example of this may be the way that some male ground
birds fight - in the case of the bantam, each attempting to exert his
dominance over the other by landing on his opponent's back.  The
ability to jump higher and control where you land more accurately
would then be favoured by sexual selection.  Again this is purely
speculation and would need to establish whether this type of
interpersonal combat came about as a result of the inherant ability to
fly.

Do we have the big maniraptor hind claw to thank for the development
of skilled climbing?  One thing our bird's earlier climbing ancestors
had that their contemporaries do not, is the famous crampon-like toe
and its stabbing action.  Is there anything in the fossil record of
trees to indicate that they may have used these to scale smoother
trunks?  punctured tracks in the bark perhaps?  Would that sort of
activity be preserved, and if so, would it be recognisable?  in the
absence of any "smoking gun" evidence like a shard of claw embedded in
the tree, or traces of tree sap build up under the claws, how much can
we infer from the scars on a petrified tree?

OK, going to stop now before I descend into incoherent and wildly
irrelevent musings.

Cheers,

On 5/23/07, Dann Pigdon <dannj@alphalink.com.au> wrote:
Tim Williams writes:

> I thought this was true for all maniraptorans.  The palms face inwards,
> but the hindlimbs are held vertically and restricted to parasagittal
> movement.  Whether this combination is suitable for trunk-climbing is a
> totally different question.

This is pretty much how cats scale a vertical trunk. Foreclaws grip the
sides of the trunk, while hindclaws mostly face forward to provide traction.
Other (more arborial) species that can rotate their ankles to grip
side-to-side are capable of decending a trunk head-first, since their fore
and hind feet can swap roles. Cats can't do this, and have to back down a
vertical trunk slowly (or wait for the fire department).

There's a simple way to demonstrate this up close. Put a cranky cat on its
back and try to tickle its belly. Your hand will be gripped mercilessly from
side-to-side by the manual claws (causing puncture wounds), while the pedal
claws will pump back and forth in a more saggital plane (causing
lacerations). Try it and see...

___________________________________________________________________

Dann Pigdon
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://heretichides.soffiles.com
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