Re: Feathered Dragons: Studies on the Transition from Dinosaurs to Birds

["David Marjanovic" <david.marjanovic@gmx.at>]

Grr. I start a thread and then I don't have time to continue. Oh sweet
weekend...

----- Original Message -----
From: "Jaime A. Headden" <qilongia@yahoo.com>
Sent: Monday, April 26, 2004 12:19 AM

> David Marjanovic (david.marjanovic@gmx.at) wrote:
>
> <Oh yes -- but the position of mt I, namely at the distal end of the
> metatarsus, and the great length of its toe are pretty convincing.>
>
>   Convincing of what? What is the mechanical advantage of the metatarsal
> 1, not preserved in *Epidendrosaurus* being located distally?

That the 1st digit is on the same level as the others.

> For that matter, why would the hallux be "non-reversed"/heterodactyl

?
Heterodactyl means toes I and II face backwards and III and IV forwards.
Only known from trogons.

> if it was an opposable digit? Two many unknowns for that matter to be
"unequivocal," as
> you put it. One may be convinced, but the data is rather equivocal with
> the two known specimens preserving opposite orientations from one another.

Preservation doesn't count. The shape of mt I does (twisted vs. not)... and
it's too flat for me to judge in *Scansoriopteryx* (the book has finally
arrived).

> With large feet and a distally placed first digit, one can also assume
> there was a weight-distribution advantage, and that can have lots of
> benefits in a wet, soggy environment such as a lake shore in a wooded
> area, or a marshy one, as one sees in small segnosaurs in the area
> (*Beipiaosaurus*) and numerous "prosauropods". The argument here is
> equivocality.

Such a small animal should have had such weight-bearing feet for walking on
normal wet forest soil? BTW, in the prosauropods it's just plesiomorphic,
and the segnosaurs it's an adaptation to standing instead of running.

> <:-) That's what I mean. It makes an arboreal lifestyle rather
> improbable.>
>
>   No, it doesn't. It means limb grasping is excluded as a means of
> locomotion. This is different. Neither sloths nor brachiating apes use an
> opposable digit when locomoting, but do this effectively well simply
> because a thumb or everted hallux is unncessecary. No, I am not implying
> brachiating feet in scansoriopterygids, but using this as a method by
> which many chiefly arboreal animals manage without a reversed hallux.

This means you either imply some hanging style of locomotion, or a
completely unknown one, or you simply think they weren't arboreal in the
first place.

> Chickens and waterfowl still manage to perch without an engaging hallux,

They all have reverted halluces of around scansoriopterygid proportions.

> There's more ... cats ... animals can climb without using
> trees, such as rocks, and still don't need opposable digits, as in
> mountain goats....

...all of which can pronate their arms (those of goats are even locked that
way), and while mountain goats hop rather than climb, cats have FAR more
mobile limbs than any dinosaur dead or alive. And they _still_ aren't
arboreal, but only scansorial.