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FW: The Roosting Hypothesis



From:  don ohmes <d_ohmes@yahoo.com>



1) as GSP observes, the presence of non-retractable, sharp-pointed, curved
claws on a fossil proves -- that individual animal did not run on solid
ground daily in the days/weeks prior to death, putative terrestrial
adaptations notwithstanding. I note that
 the abrasive qualities of various forms of cellulose do not match those
of silicates.

2) excluding the terminal branch environment, a reversed hallux is not
mechanically essential to either claw-climbing or sheltering in the
majority of trees. Despite handwaving to the contrary, small animals do
not _have_ to grip surfaces in opposable fashion
 to remain on them, are unlikely by species to fall over when they sleep
(see flamingos for an extreme example), and are unlikely to be injured in
the event of a fall.

3) the mechanical need for mammalian-style flexibility in simple quad
claw-climbing is imaginary. The front-limb sequence is extend/attach/pull,
and the hind-limb swings forward/attaches/pushes.

4) a ground-foraging, tree-roosting (GFTR) animal begins each foraging
cycle by descending from the roost. Any adaptation that increases the
horizontal reach of this initial descent increases fitness. This includes
adaptations that allow descent from greater
 height, as well as the obvious desirability of increasing glide ratio.
In a bipedal GFTR animal, the front-limbs are "free" to evolve, while the
hind-limbs are conserved by daily foraging. The power of daily foraging to
shape the hind-limb is demonstrated by M. gallopavo, if one assumes that
it is derived from a smaller perching
 ancestor. I add that personal observation has convinced me the turkeys do
not use the hallux in roosting, even on smaller branches.

Summing -- it follows that a trees-down path to powered flight *can* occur
in the absence of a reversed hallux or "arboreal adaptations".
GSP's claims re curvature will do much to define future discussions if
they hold up -- given the presence of sharp claws on even one fossil, I am
optimistic...
Sent from Yahoo! Mail on Android

________________________________________
From: Jason Brougham <jaseb@amnh.org>;

To: david.marjanovic@gmx.at <david.marjanovic@gmx.at>;
<"dinosaur@usc.edu"@listproc.usc.edu>;

Subject: The Roosting Hypothesis
Sent: Fri, Jul 12, 2013 1:58:54 PM


Not much research has been done into what animals are capable of at the
edges of their abilities. Like pinioned pochards climbing 6 foot fences,
or 1 day old chukars climbing 60 degree inclines.

Yet, this must surely be where selection pressure is strongest and where
evolution happens. If a population of animals is routinely at the edge of
its physical capabilities, any mutation that helps would likely be
incorporated into the gene pool and propagate
 rapidly.

Ken Dial has done the most work on this subject, probably, though he is
reallyh interested in the flapping aspect. Nonetheless he found that
ground based birds don't even bother flapping their wings until they are
climbing an incline steeper than 45 degrees.
 And 1 day old chicks climb 60 degree inclines just by pushing down with
their forelimbs, not really flapping.

There are a lot of fallen branches and snags reaching the ground at 60
degrees or less in any wild forest after every big storm.
________________________________________
From: owner-DINOSAUR@usc.edu <javascript:return> [owner-DINOSAUR@usc.edu
<javascript:return>] on behalf of David Marjanovic
[david.marjanovic@gmx.at <javascript:return>]
Sent: Friday, July 12, 2013 9:43 AM
To: dinosaur@usc.edu <javascript:return>
Subject: RE: Yet more on pterosaur quad arm posture

> OK, my incredule, here is a flightless Weka (Gallirallus australis) in a
shrub:
>
> http://www.flickr.com/photos/trs/3476131920/
>
> And, as I say, chicks and pinioned birds that can't fly do it too.

Let me just quote from what it says under the photo:

"Wekas really aren't meant to be off the ground, and the best part was
when this particular one kept falling off the branch. I saw this silly
bird on Ulva Island, a small island in a bay of Stewart Island."

"The tree was more of a large shrub, and it hopped up from branch to
branch."

Seriously, this does not count as climbing.

> Of course Strigops does as well, but it is zygodactylous, after all.

It's a parrot. Parrots _are_ good climbers.