Re: Campbell's even crazier than a MANIAC? (archeopteryx

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

Did I mention that I have accumulated a large backlog?

----- Original Message -----
From: "Sim Koning" <simkoning@msn.com>
Sent: Wednesday, September 24, 2008 9:16 AM

> I know you've seen this comparison 100 times, but how heavily does 
> dromaeosaurid anatomy differ from that of a hoatzin chick 
> http://en.wikipedia.org/wiki/Image:Hoatzin_chick.jpg

Indeed not terribly much. Two big differences, however, are the beak which 
can be used for climbing -- the teeth of most, perhaps all, dromaeosaurids 
look like they'd be damaged if used that way -- and the perching foot; look 
at that reverted and endless first toe, its distal position on the 
tarsometatarsus, and its curved proximal phalanx in the picture you mention.

> Also, the greatly elogated digits of an Archaeopteryx manus could have 
> been entirely an adaption for an arboreal lifstyle.

They are not elongated at all compared to other maniraptorans. They don't 
need an explanation. And incidentally, they are considerably longer than a 
hoatzin's.

> Iguanas have greatly elogated toes for exactly same reason, and they lack 
> pretty much any other adaptation for arboreality, yet they are habitual 
> tree climbers.

That's because lepidosaurs in general are decent climbers, with limbs that 
are mobile in several directions at most joints for example.

> In fact the greatly elogated 3rd digit of an Epidendrosaurus manus closely 
> resembles the elongated toes of an iguana's foot.

To me it looks like if this animal used anything for climbing, it was the 
first two fingers, not the third, which is lengthened so it can be stuck 
into holes in trees...

> Given real world examples such as iguanas, which have virtually no 
> morphological differences from ground dwellling lizards (except for their 
> elongated digits) I don't think it's easy to say Archaeopterx was not a 
> habitual climber simply because it doesn't have more than one adaptation 
> for climbing.

Ground-dwelling lizards make good climbers. Ground-dwelling dinosaurs not so 
much.

> The fact that they seem to be well adapted for running along the ground 
> could simply be evidence of Archaeopterx striking a balance between an 
> arboreal and cursorial lifestyle.

Its toe claw curvature and its toe phalanx length proportions are in fact 
intermediate (just on the terrestrial side of things, but borderline).

> It IS easier to become airborne from an elevated position

If you already are in an elevated position.

> and you can also travel much further.

Which may or may not be an extra advantage.

> Plus after jumping it would immediately begin to slow down, and in the end 
> it would have been better off simply running.

If speed was what was selected for.

> I think it does, simply because there has to be a transition between a 
> simple fall and powered flight, and gliding is much less energy consuming 
> than flapping your wings to achieve what is basically a prolonged fall. 
> Yes I guess an animal could flap its wings to prolong its fall, but why 
> waste the energy when it could achieve the same thing by evolving a larger 
> wing surface to simply glide.

I don't think the evolution of gliding -- in any of the 10 or whatever 
cases -- ever involved a fall as an initial stage. I think it more likely 
evolved directly from jumping from branch to branch.

I could imagine that flapping flight could directly evolve from trying to 
catch insects with the forelimbs in mid-air while jumping from branch to 
branch, and the bats are an obvious candidate for that having actually 
happened. That's probably a rather useless speculation on my part, but, as 
long as it isn't falsified, it means we can't assume that flapping must 
necessarily have evolved from gliding in every case of a trees-down origin 
of flight.