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Re: 11th specimen of Archaeopteryx‏

On 11/7/2011 6:37 PM, Tim Williams wrote:

If basal paravians did roost or perch on branches, why didn't the pes
become opposable?

Because it is not necessary to roosting, and therefore does not enhance reproductive success in animals that find safety in trees.

Using "perch" in the technical sense (gripping a small round-ish limb) -- yes, of course a modified pes is necessary.

But, unless we are pretending that all branches are <3 cm in diameter, then perch-roosting is a subset of roosting.

A roosting lifestyle does not inevitably lead to a perching lifestyle, therefore sleeping in trees does not inevitably lead to "arboreal adaptations" -- it only requires minimal talent.

One argument raised against this is that a
cursorial/ground-foraging lifestyle deterred the development of a
hallux suitable for perching.  I frankly don't believe this.  Many
modern birds forage on the ground and roost in trees, and the hallux
is long enough to be employed for perching, and elevated enough to not
interfere with walking or running.

So what? Aren't these modern birds presumably secondarily ground foragers, and descended from fully optimized perching birds, which in turn presumably descended from fully optimized non-knee-walking cursorial bipeds?

Why assume the transition (perching pes to cursorial+perching pes) mirrors the original cursorial to perching transition, especially given the major differences between the M. gallopavo condition and the generic theropod condition?

A scenario in which the perching pes came after powered flight implies that the perching pes is an adaptation that occurred in animals that a) no longer needed to escape predation by running, and b) that could fully utilize trees.

It is a great leap to speculate that any tool design optimized to one task can be readily made into a combination tool w/out some loss of function in one or both applications.

So IMHO, the reason why basal
paravians like_Archaeopteryx_  didn't have a pes adapted for perching
is simple: They didn't perch.


Or roost.

That does not follow.

And fair warning -- if you claim or imply that sleeping animals tend to topple over, I will insist that you image-google "sleeping flamingo".