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

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Keesey wrote:



> They have other arguments as well -- I'd suggest re-reading the paper.


I read it a few times, just to make sure I understood their reasoning.  Another 
of their arguments (which you quote from below) is particularly mystifying...


> They key one, to my mind, is this: "attaching the name 'Aves' to the
> dinosaur crown maximizes the number of safe inferences that can be
> made about the ancestor of the clade designated by that name; it
> therefore also maximizes the number of generalizations that can safely
> be made about birds as the group composed of that ancestor and all of
> its descendants."


First of all, it implies that the term "bird" should be limited to the 
crown-group, which I think is a big no-no.  (I know that's not the intention, 
but I think we have to be careful in associating the word "bird" too closely 
with the crown-group only.  I especially like Jeff Hecht's reasoning for why 
this should be avoided.)


Secondly, I'm not at all sure what maximization of either "safe inferences" or 
"generalizations" regarding hypothetical ancestors have to do with clade 
definitions.  Does this really matter?  Don't forget that the crown-group Aves 
definition not only casts _Archaeopteryx_ out of Aves, but also _Ichthyornis_ 
and _Hesperornis_ as well.  We may not be too confident about our inferences 
regarding_Archaeopteryx_ (including even whether it flew or not), but we are on 
much safer ground when it comes to _Ichthyornis_ and _Hesperornis_ - both of 
which would be non-avian under Gauthier and de Queiroz (2001)'s definition.


Thirdly, we already have a name for the crown-group: Neornithes.  Further, 
Neornithes has been used for the avian crown-group for a very, very long time.  
[Gauthier and de Queiroz (2001) propose a whole new definition for Neornithes, 
and make it *more* inclusive than Aves!]


> (This is after establishing the fact that the name
> "Aves" is by far the most-used of all the names they define in that
> paper.)


Yes, that's certainly true.  But by the same token, given that "avian" tends to 
be used both as (1) an adjective and noun equated with "bird"; and (2) a member 
of clade "Aves", I think it would be useful if "Aves" includes all those taxa 
that have traditionally been considered "birds" (avians).  Thus, I think it is 
preferrable to leave _Archaeopteryx_ in Aves, where it's been ever since its 
discovery.



Cheers

Tim
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