Re: Perching, climbing, roosting was Re: 11th specimen of Archaeopteryx

[Don Ohmes <d_ohmes@yahoo.com>]

On 11/10/2011 12:42 AM, Tim Williams wrote:

> The hallux could easily have become better
> adapted for grasping branches, without interfering with a
> ground-foraging lifestyle.

Special pleading, and you ignore the arithmetic.

There is no evidence it can be done starting w/ a generic theropod pes 
w/out first passing through a perching-only phase, and absolutely zero 
support for an enhanced survival value accruing to claw-climbing animals 
that roost in trees, but forage exclusively on the ground.

Unless we continue to pretend that all trees have only small branches 
and small animals w/ claws are insecure in trees, and fall over when 
they sleep, like humans do. And that giant dinosaurs thoroughly comb the 
tree-tops at night, searching for snacks that apparently too deaf to 
hear them coming and flee...

But even under such unreasonable assumptions -- of the total variance 
possible in pes design per replication, there is a limited pool of 
fortuitous design variants, relative to "perching" -- of that pool, 
there is only a subset of variants that do not in any way interfere w/ 
terrestrial locomotion.

The increase in survival probability would need to be very high indeed 
for such unlikely changes to occur and be conserved in the face of the 
thousands of high-stress steps taken daily while foraging by not only 
the animals considered, but their ancestors as well.

Given that you cannot demonstrate such an increase in survival, even 
hypothetically, we are more or less engaging in mysticism to consider 
lack of change in the hallux  as evidence roosting did not occur in 
pre-birds.

> Modern ground-foraging birds show us how
> it can be done (turkeys, peafowl, secretary bird, etc etc). There is
> no reason to assume that ground-foraging and roosting impose competing
> selective pressures on the foot.  Turkeys etc do both quite well.

Bad analogy.

As previously stated -- presumably turkeys (American-style) are 
descended from perching ancestors.

As previously stated -- adapting a perching foot to terrestrial foraging 
in an animal w/ full flight powers does not parallel the process of 
creating essentially the same design in an animal that begins w/ a 
generic theropod pes and has limited (or no) active flight talents.

Previously mplied -- the turkey pes is moving toward the terrestrial 
condition, not away.

Even so -- although turkeys run well for birds, they would be quickly 
eaten into oblivion should their wings be clipped, or even be similar to 
Archie + immediate ancestors.

So explain how you know that there are no trade-offs between 
terrestrial-only and perching + terrestrial?

> And yet... while roosting, most modern birds that roost secure
> themselves to the bough/branch using an opposable pes.  Such as your
> good friend _Meleagris gallopavo_, the turkey.

Sigh. They are modern birds. They ALL descend from perching ancestors. 
And are very tasty. And make a bad analogy...

> Again, roosting is not as "simple" as you make it sound.  It is not
> simply standing/crouching/huddling/squatting on a bough or branch as
> you would on the ground.

Sure it is. Claws, Tim, they had claws...

> Even a small shift in position can be fatal,
> so it helps to be adequately secured to the substrate (bough, branch,
> whatever).  Both gravity and an uneven substrate are conspiring
> against you.

I am sorry, but the above is quite ridiculous. Not likely even a long 
and unimpeded fall would kill or even injure an Archie-type. And how 
likely is a fall, unlikely in itself, to be unimpeded?

Even as an old man on crutches, I have no problems staying in an 
appropriately sized/shaped tree -- the problem is getting out. Be nice 
to have glider wings.

When young, 'no hands, mom' was just plain fun -- when an adult, 
claw-climbing was sometimes a daily activity and falling was a risk that 
never manifested itself, even when in trees deliberately chosen for 
difficulty.

To posit that the vastly superior Archie-type body would be insecure in 
a tree is beyond drama...

> Briefly, climbing up trunks and foraging within the crown promotes
> different adaptations.

The mechanics (vernacular sense) of foraging in trees logically promote 
perching (i.e., the ability to grasp small branches). Especially 
flight-foraging, as landing on a small branch is tricky.

Roosting, not so much -- if small branches are a problem, you just avoid 
them...

You stated (iirc) that flight precedes perching in the record. That is 
not surprising.