Re: semilunate carpal

["Tim Williams" <twilliams_alpha@hotmail.com>]

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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