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Re: FW: Re: FW: Help with Cladistics



At 1:46 AM 8/31/95, James Shields wrote:
>>        "Non-avian dinosaurs" may have possessed plumage.  They may also
>>have been neon blue, wore tutus made of ginkos, and been hunted to
>
>Your point is entirely correct. It is worth noting, however, that the
>feathers in Archaeopteryx are well developed - to the point whare they are
>asymmetric, indicating that they were active flyers. My point is that
>feathers didn't evolve from scales overnight, and there must be a line of
>intermediate species with various developments of feathers. Until we find
>more skin impressions we cannot even guess where this line begins and ends.

        YES, YES!!! bingo!!
>
>It is nor a good idea to try to seperate dinosaurs from birds on the basis
>of rarely preserved features such as feathers, and from skeletal features
>alone it is very hard to call Archaeopteryx a bird.

        As long as phylogenetic analysis utilizes derived characters (via
homology) to define the status of taxa, and as long as feathers are
considered a synapomorphy for birds, the feathers of Archaeopteryx include
it w/ in aves.  Other fossil birds, for which there are no feathers, are
included w/ in aves on the basis of their possession of osteological
synapomorphies for birds.
        Here's an idea to throw to everyone:  Since the improvements in our
understanding of the evolutionary relationships between taxa should be
expressed as much as possible (for the obvious R &P reasons), why doesn't
everyone who loves paraphyly so much simply make theropoda paraphyletic w/
respect to aves?  Thus, we expand our concept of Dinosauria to include all
the taxa who have EVER evolved from a common ancestoral proto-dino' (and
include it as well).  Several weeks ago, I spouted off about the advantages
of paraphyly, but some of it is getting pretty extreme.  If you want to
talk about a particular lineage of critters w/out the lineage of their
descendants, fine, but some of this stuff (EG "thecodontia") is reaching
the point where undefinable groups are being discussed.  How??  Give me
morphology, behavior, ANYTHING that defines "thecodontia", per se, and I'll
shut up.

        Sincerely,
>
>





Jason J. Head
Dept. of Geological Sciences
Southern Methodist University
Dallas, Tx. 75275