[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Campbell's even crazier than a MANIAC? (archeopteryx climbing)



--- On Sat, 9/27/08, Tim Williams <twilliams_alpha@hotmail.com> wrote:

> If the areas between modern trees are literally buzzing
> with insects, why isn't this niche ripe for exploitation
> by an incipiently flapping, gliding insect-eater?

Because it is currently filled w/ _highly sophisticated and voracious_ flapping 
insect-eaters. The phrase "...nothing to eat there" was meant to point out the 
fact that occupying the "empty morpho-space" of which you speak means competing 
directly w/ vastly superior creatures for the food in the REAL space your 
"incipiently flapping, gliding insect-eater" must live in. 

"You can't get your foot in the door when Big Mama is standing in it." -- 
anonymous wisecracker.

> As for our ancient batty friend _Onychonycteris_... lack of
> echolocation might have made aerial hawking difficult at
> night.  Because _Onychonycteris_ seems to have been
> insectivorous, it may have obtained insect prey mostly by
> gleaning.  

Sure. And/or accidental collisions while gliding from tree-to-tree, leading to 
hawking and echo-location. The space between the trees was presumably 
under-exploited by insectivorous birds at night. Hence the success of the bats 
at moving in.

> > Quite correct. Acquiring prey by gliding simply
> isn't going to work when birds are around, but commuting
> is always an open option if you have a job to go to...
> 
> Again, an apparent contradiction.  If obligatory biped Don
> Ohmes can encounter flying insect populations in his
> tree-to-tree excursions (presumably terrestrial) - why are
> these same hordes of insects beyond the reach of a modern
> aerial glider?

Competition. Unless you know of an insectiferous arboreal environment that is 
presently free of bats and birds???

> > Also, the debate IS a dichotomy in the sense that you
> HAVE to start somewhere. Once the ball is rolling, the
> dichotomy disappears, but that first step is is a 
> > booger...
> 
> Yes; but the "first step" is not dictated by
> relative ease.  Natural selection can only act on what's
> already available.  

Exactly! On the gravity-driven side, you have every animal that can or will 
leap, fall, or pounce from a high place for natural selection to act upon. On 
the muscle-driven side, ya got nothing but your imagination and a long list of 
"ancestral constraints". As any manufacturer can tell you, the availability of 
feedstock and ease of manufacture all count when assessing the likelihood of 
success.

> The decision about which side of this
> (alleged) dichotomy is more likely to have occurred -
> "ground-up" or "trees-down" - should be
> based on the ecomorphologies of those taxa closest to the
> origin of flight.  

Exactly! This is why the "climber-friendly" nature of cycads is important. 
Cycads can be utilized by animals that are optimized for non-arboreal forms of 
locomotion. Roosting, perch-hunting, gleaning, even nesting are physically 
possible, and arguably advantageous...

> So *a priori* assumptions about which
> pathway is "easier" are utterly irrelevant,
> because natural selection does not have the luxury of making
> such choices.  Even if I were to concede (which I won't)
> that "trees-down" is "easier", it cuts
> no ice with natural selection.  As long as
> "ground-up" (or at least some kind of
> cursorial/terrestrial contribution to the origin of flight)
> is biophysically/biomechanically possible, there's no
> reason why it can be considered less likely than
> "trees-down".  
> 
> In other words, it makes no difference if gliding is
> "easier" than leaping upwards to catch insects, if
> the former behavior never existed in the ancestors of birds.

I did not realize the the non-existence of gliding behavior in proto-birds had 
been proven...

> Something lead to flight, and I don't think that
> preconceived ideas of what these theropods *should* have
> been doing (because it's less biomechanically or
> biophysically challenging) are relevant.

'All events "biophysically/biomechanically possible" are equally likely', and 
'long chains of critical events are as probable as short chains of critical 
events' is what this boils down to. Even if you manage to define a threshold 
that separates "impossible" from "possible", I don't think you will find 
overwhelming (non-political) support for these ideas. 

I would also recommend avoiding the poker table, although that might be good 
advice for everyone in any case. :D

Don