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Re: 11th specimen of Archaeopteryx



Don Ohmes <d_ohmes@yahoo.com> wrote:

>> Secondly, if theropods *routinely*  spent time in trees we might expect
>> to see arboreal specializations.
>
> Not if the time spent was unrelated to locomotive activity. As in, roosting
> -- but not foraging, mating and etc.


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?


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.


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.


> So I disagree strongly -- arboreal specializations are NOT expected in an
> animal that roosts, but otherwise pursues it's daily (or nightly) business
> in cursorial fashion on the ground.


I would have said roosting would require some arboreal specializations
- like a branch-grasping pes.  Ground-foraging birds that roost at
night (such as turkeys, peafowl, and the secretary bird) all have a
hallux that is eminently suitable for grasping branches (perching).


> What, then? Cliffs?


>From an intuitive perspective, I think it is plausible that small
paravians occasionally foraged in trees.  We know some of them ate
seeds, and some probably ate wood-boring insects.  So what if these
paravians scaled trunks to get food, then glided back to earth?  No
roosting or perching required, because the time spent in trees was so
brief.


> Assuming constrained powerstroke and no obvious arboreal adaptation are
> facts in the animals that represent the transition between feathered
> theropods and winged flyers, a ground-foraging tree-roosting (GFTR)
> lifestyle is about all that is left.


Before we embark on an acronym war, I think I can say we actually
agree on the major points: A gravity-assisted origin of flight among
small paravians that were predominantly terrestrial, with trees being
the platform for aerial launches.  We just disagree on the issue of
roosting.





Cheers

Tim