RE: smallest ANCIENT non-bird dinosaur - was what I was asking

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Keesey wrote:



> The reasons are pretty well-argued by Gauthier and de Queiroz (2001).


The reasons are argued by Gauthier and de Queiroz (2001).  But I don't think 
their reasons are "well-argued".  :-)  Their logic seems to be that, because 
Linnaeus did not include fossil taxa in his "Aves", then the name "Aves" should 
be limited to the crown group.  Never mind that Linnaean didn't know of any 
"fossil taxa", or even know about "evolution".


>> I think in this case we can have our cake and eat it too. Aves can keep to 
>> its traditional usage and be a node-based clade that is defined to include 
>> _Archaeopteyx_;
>
> The position of _Archaeopteryx_ (which is a very early taxon) seems
> too volatile for this to be very useful. 


Actually, _Archaeopteryx_ has been a very stable taxon, phylogenetically 
speaking.  Almost every tree I have seen has it as the sister taxon to all 
other "birds", at the base of a clade that includes it and all these other 
"birds", but not deinonychosaurs, oviraptorosaurs, etc.  This clade deserves a 
name, and we might as well use "Aves" - considering it has 150 years of 
precedence for this content.


> Besides, it's only historical
> accident that makes _Archaeopteryx_ so interesting. 


That may be true.  But that doesn't detract from the fact that it *is* 
interesting.  It's the earliest and most basal know "bird" for which we have 
anatomical evidence for powered flight.  (Plus, there are many other reasons 
why _Archaeopteryx_ is interesting.)


> Really, I question
> whether giving this clade any name is useful.


Using that rationale, it's not much point giving *any* clade a name.  Even 
"stable" taxa bounce around to some degree, if only because certain taxa around 
them are unstable.  All this means is that definitions should be framed very 
carefully - especially regarding the choice of positive and negative specifers.


>> and Avialae can be retained as a stem-based clade that specifically excludes 
>> deinonychosaurs.
>
> It was intended as a name for the clade of volant dinosaurs and
> redefined as such (again) by Gauthier and de Queiroz (2001). (The
> branch-based definition was an early stab at this.)


That second definition (Gauthier and de Queiroz, 2001) actually used powered 
flight as the *definition* for Avialae.  Such an "all-or-nothing" definition 
("flight-or-no-flight") is almost impossible to apply to many fossil taxa, 
including _Archaeopteryx_.  Sure, _Archaeopteryx_ was *probably* capable of 
powered flight; but we are never going to be able to test for it.  The converse 
is true for _Microraptor_ (probably incapable of flapping flight, but not 
testable).


> Whether or not it's the exact reason, it's a pretty pervasive pattern:
> chicken/poultry, sheep/mutton, deer/venison, swine/pork, calf/veal.
> (In all cases, the name of the animal is from Anglo-Saxon and the name
> of the meat is from Norman French.)


Yes, those were the examples I heard too.  Damn, now I'm hungry....


Cheers

Tim
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