Re: Fossil Discovery Threatens Theory of Birds' Evolution

[NJPharris@aol.com]

In a message dated 6/26/2000 6:08:02 AM Pacific Daylight Time, 
tholtz@geol.umd.edu writes:

> > Personally, I'd prefer the apomorphy-based definition: Mammalia =
>  > {the first
>  > ancestor of modern mammals to possess a single lower jawbone + all of its
>  > descendents}; but, alas, it was not to be.
>  
>  Tsk, tsk, tsk...
>  
>  Please don't confuse "definition" with "diagnosis".  Definition, in PT, is 
a
>  statement of common ancestry.  Diagnosis remains a list of derived 
character
>  states optimized at that particular node.

Hey, now!

Please read what I wrote.  This is a definition (albeit not a PT one), not a 
diagnosis.

And I was very careful to state "the first ancestor *of modern mammals* to 
possess a single lower jaw bone" to avoid a potential polyphyletic mammalia 
should that feature prove to have evolved more than once.

Nick P.