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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...