RE: Microraptor hanqingi, new species from China.

[Jason Brougham <jaseb@amnh.org>]

Fire caves, from forest fires in conifer forests, are plenty big enough for 
nesting. I've observed many of them in the Cascade Mountains. Condors nest in 
them. I would assume, from what I've read on Jurassic charcoal, that Mesozoic 
forests were rife with them

Other animals, such as Marbled Murrelet, roost and/or nest on the surprisingly 
flat upper surfaces of large limbs, and their crotches. In modern redwood 
forests these surfaces are large enough to support stands of ferns and 
huckleberry bushes.

Also I have photographs of the Diving Petrel, which lacks halluces, nesting on 
wide boughs and roosting in slender branches. Of course they get up there by 
flapping flight, but then they scramble around just fine.

I suppose there is some value to pure a priori reasoning and hypothesizing, 
like "to sleep in a tree, you need a way to hold yourself in there _while 
sleeping_". It is good to let one's mind rove in creative ways and to make 
clear, unqualified, proposals as part of reasoning. But whenever I catch myself 
making an assumption like that it feels really good to quickly scan the 
literature and confirm or deny it. It turns out to be definitely false in the 
case of Diving Petrel.
________________________________________
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of David 
Marjanovic [david.marjanovic@gmx.at]
Sent: Thursday, May 24, 2012 12:29 PM
To: dinosaur@usc.edu
Subject: Re: Microraptor hanqingi, new species from China.

> >   But if you're a theropod, and you want to spend a large
> > part of your life sitting on boughs or branches, you need to have a
> > way of holding on.
>
> This is an active hypothesis, and requires evidence.
>
> And good luck on that -- it is mechanically incorrect relative to mere
> sitting or even standing on large, more or less horizontal
> branches/crotches by even inanimate objects, much less well-clawed
> theropods that presumably had reasonably competent balancing systems --
> "large branch" being defined as relatively rigid, and significantly
> larger in diam
> theropod balances.
>
> Moreover, there is no obvious selective path to a perching foot in the
> presence of active ground-foraging, the absence of active in-tree
> foraging, and/or exploitation of small, flexible branches, such as are
> found in the terminal branch environment.

Who cares about "obvious"? :-) We've discussed the Fowler et al. paper in PLoS 
ONE about the prey-grasping function of the dromaeosaurid foot. That's a good 
starting point for a branch-grasping foot (even though it _isn't_ a 
branch-grasping foot itself).

I think sleeping in trees came next-to-last, followed only by nesting in trees. 
That's because to sleep in a tree, you need a way to hold yourself in there 
_while sleeping_. That can be a specialized foot, a big hole in the tree, or a 
nest; ways of building nests in trees may not be very easy to evolve, and 
finding holes big enough for anything the size of *Archaeopteryx* or 
*Xiaotingia* or *Anchiornis* or any kind of *Microraptor* is difficult. -- I'm 
sure I've overlooked other possibilities. What are they?