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Re: semilunate carpal



Dinogeorge wrote:

<< I thought Caple, Balda, and Willis on their paper on the physics of
preflight pretty convincingly argued that the ground-up track was physically
and mechanically possible, and that even small development of feather-like
integument would aid a cursorial predator. >>


But the other track, that is, from arboreality to flight, is surely >even
more possible<.

Yes, but "even more possible" doesn't enter into the equation. Evolution works on the raw material it has available. Sure, it's theoretically easier to achieve flight with the assistance of gravity, since the leaper/glider can use it to achieve airspeed. However, as long as a "ground-up" hypothesis is theoretically *possible*, it cannot be dismissed on the basis that it's "less feasible" than a "trees-down" origin.



E.g., a small development of feather-like integument would
also aid an arboreal animal, partuclarly in ameliorating the Falling Problem.

Here I agree with you 100%. I like to think this animal was something like _Microraptor_.



 [snip](_Microraptor_, _Sinornithosaurus_...). >>

These are all Late Jurassic or younger. I'm talking about Middle to Late
Triassic, which is where the common ancestor of Coelophysis and birds is to
be found. This common ancestor was probably small (crow-size), and likely had
a featherlike covering, pneumaticized skeleton, large (grasping) four-digit
forelimbs, prehensile feet, and a long, feathered tail. (Gee--does this sound
like Chatterjee's reconstruction of Protoavis? Purely coincidental?)

Apart from the four-fingered hand and prehensile feet, it could be almost any small theropod. (And does _Protoavis_ have prehensile feet?)



All
these features can be directly inferred from known fossils of Coelophysis
and, say, Archaeopteryx. Does this animal seem more like a bird or more like
Coelophysis?

It seems like a pretty average small theropod to me. I think you're putting your topsy before your turvy. Most of the "bird"-like characters you allude to are theropod characters inherited by birds (bipedalism, feathers, pneumaticized skeleton, long forelimbs and hands...), so inferring that the first theropods were probably very bird-like is hardly a revelation.


BCF seems to be presupposing that all "bird-like" characters are observed in terrestrial theropods because they were passed on from birds to theropods. The prevailing view, on the other hand, is that birds inherited most of their defining characters from theropods, feathers included. The latter interpretation has the advantage of having excellent corroboration from the fossil record. BCF comes up a little short in this respect.


Tim


---------------------------------------------------------------------

Timothy J. Williams

USDA-ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163




---------------------------------------------------------------------

Timothy J. Williams

USDA-ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163




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