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Re: 11th specimen of Archaeopteryx
On 10/30/2011 10:50 PM, Tim Williams 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.
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.
In particular, the presumable basal ground-nesting condition would
obviate a transition to arboreality. What arboreal animals (in terms of
skeletal morphology) are ground-nesters? Are there "perching" birds that
nest on the ground as a primitive condition?
I certainly agree with you here. The "limited powerstroke" was not a
good recipe for fighting against the force of gravity (which is the
essence of "gound-up").
What, then? Cliffs?
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.
Note that all the clever ground-based activities advanced over the years
(fighting, leaping, brooding and etc.) nestle neatly into a GFTR
lifestyle -- possibly all at once in the same animal.
GFTR just provides a daily gravity fix, which in turns provides a
straight-forward path from the generic small wingless feathered theropod
to a passive flier to real bird. And real birds, as you point out, can
fly into trees rather than grunt their way up -- and as such are free to
perch in them permanently.
In this view, Archie is an important 'transitional' fossil in the
functional sense -- irregardless of living descendants, yea or nay...