Re: 11th specimen of Archaeopteryx

[Jason Brougham <jaseb@amnh.org>]

I have heard Paleontologists, including Chinese ones, suggesting that Mei did 
roost on the ground just like geese do today. The idea that the type specimen 
is displaying a roosting behavior (as opposed to an emergency sheltering 
behavior) held in common with modern birds is also discussed in the monograph.

This has been an excellent discussion of the enigmas of arboreality in 
paravians. I would just add this.

In discussing this we are discussing animals, perhaps one lineage of animals, 
where evolutionary transitions were occurring (where one lineage gave rise to 
proper birds). I am not an expert on evolutionary theory, but there must be a 
state that sometimes occurs in evolutionary transitions where organisms have 
not yet adapted anatomically to a new function or habitat, but are instead 
adapting by sometimes straining to the maximum of their physical abilities. 
This strain, in turn, provides the natural selection that leads to the 
anatomical adaptation. In other words, some small paravian or basal bird was in 
trees without a hallux, and this provided the selection pressure for a hallux 
to evolve. It is the same with powered flight. There must have been animals 
that  were poor and tentative fliers, that lacked large sternal keels, and in 
which the selection pressure for a large carina arose. Now, of course, I know 
that this is adaptationism, and I am skeptical of strict adaptationism, but 
there must be a subset of cases in evolutionary history where features arose 
not sheerly through exaptation or evo devo consequences, but through simple 
adaptation: If you have a slightly better grip on the branch you are  a little 
more likely to survive and leave offspring who also survive.

It may be impossible to prove definitively from fossil evidence, but the new, 
small, Jurassic paravians may be just the creatures I'm referring to. Such a  
hypothesis should be testable, though, by tracing the sequence of adaptations 
across a  better informed cladogram.

There are also known cases where a group of animals perform a function which is 
an important part of their biology and they simply never show an anatomical 
adaptation to this function, it simply never arises. I now collect photos of 
turkeys and other basal neornithines brooding their chicks in trees. Looking at 
these images the parents certainly look awkward and we'd all feel a lot more 
comfortable about the situation if they had feet like Cracids. But they don't, 
they are somewhat ill suited to this sub-habitat, and  future Paleontologists 
will probably never ever be able to demonstrate that they behaved this way.

On Oct 31, 2011, at 8:19 AM, Matthew Martyniuk wrote:

> For the record, I don't think anybody actually believes the _Mei_
> specimen died while sleeping or resting normally, but rather was
> probably sheltering itself against the volcanic ash cloud that buried
> it. Whether or not this has any bearing on normal roosting behavior, I
> don't know.
> 
> Matt
> 
> On Mon, Oct 31, 2011 at 1:32 AM, Don Ohmes <d_ohmes@yahoo.com> wrote:
>> On 10/31/2011 1:10 AM, Tim Williams wrote:
>> 
>>> I would have said roosting was related to locomotive activity, insofar
>>> as the animal would be sitting, standing or perching on (or in) the
>>> tree for long periods.  That means that it has to adopt a stable
>>> posture while sleeping or resting.  There is no evidence in the
>>> anatomies of_Archaeopteryx_  or any non-avian theropod that they were
>>> capable of this.  How did they prevent themselves from toppling off a
>>> limb, when the manus and pes had minimal (if any) prehensile
>>> abilities?
>> 
>> Just guessing -- none of you guys have ever so much as climbed a tree?
>> 
>>> Further, the 'tuck-in' sleeping posture adopted by_Mei_  seems
>>> incompatible with roosting.  Now, I'm not saying that all paravians
>>> adopted this posture, or that those that did adopted it whenever they
>>> slept or rested.  But the fact remains that Archie and non-avian
>>> paravians lack any adaptations for roosting, and at least one (_Mei_)
>>> was preserved in a posture that showed it rested and slept on the
>>> ground.
>> 
>> Interesting. The part about Mei, that is... I will read up later.
>> 
>>> Besides, I still don't see how tree-climbing qualified as a refuge for
>>> small paravians, when so many potential predators were large - at
>>> least as large as many tall trees.
>> 
>> LOL. I really do not think the mega-theropods were targeting crow-sized
>> animals, period. Or sticking their noses into thickety places.  Even should
>> that be the case -- hey, at least in a tree they would not get stepped on.
>> 
>> Walking in the woods at night it is common to disturb roosting animals --
>> they ALWAYS bail on the opposite side of the tree -- it is a very effective
>> escape strategy.
>> 
>> Good night, folks.
>> 

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544