[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Two new FAQs: Everything You Wanted To Know About Cladistics



> Date: Wed, 22 Aug 2001 21:43:41 -0700 (PDT)
> From: "Jaime A. Headden" <qilongia@yahoo.com>
> 
> Ken Kinman (kinman@hotmail.com) wrote:
> 
> <One thing I would like to see on the second one is some mention of
>  homoplasies (convergences and especially reversals), and how they
>  can sometimes trick both computers and people into believing they
>  are synapomorphies (and thus can negatively affect reliability).>
>
> I'd disagree with the inclusion of "reversals" of character polarity
> and expression as a function or aspect of homoplasy: in a computer
> analysis, they tend to pull the taxon backwards, as it were, and
> collapse nodes -- they do not make false synapomorphies.

I'm sorry, I'd like to modify the FAQ answer to take this into
account, but I don't understandf what you mean by "pull the taxon
backwards" or "collapse nodes".  Could you possibly spell it it out in
words of one syllable?

> <And on the first one, I would quibble a little with equating
>  "traditional Reptilia" with "Reptilia minus Aves". Many
>  traditionalists continue to removed both Aves and Mammalia from
>  Reptilia, and leave the traditional paraphyletic synapsids
>  (pelycosaurs and therapsids) in Reptilia. This is the way it was
>  traditionally done for much of the 20th Century, and it is still
>  often done this way outside of cladistic circles.>
> 
> And these fellows are still in academics? *shakes head in wonder* I
> thought Romer and Cox got rid of all that nonsense decades ago? I'm
> glad to see people are keeping mammals from Reptilia [...]
                                         ^^^^
           Did you mean "keeping mammals _in_ Reptilia"?

OK, I am a bit confused here.  The way I remember the tree (and I'm
not sure where I got it from) is:

                             Aves
                              /
                             /
                Crocodilia  /
      Mammalia    \    Dinosauria
           \       \      /
            \       \    /
             \       \  /
         Synapsida  Diapsida
               \      /
                \    /
                 \  /
               Reptilia

Which is what I originally used in my examples.  Then I checked the
classification in the dinosauricon, spead over the two pages:
http://dinosauricon.com/taxa/tetrapoda.html
http://dinosauricon.com/taxa/sauropsida.html
which has Synapsida _outside_ Reptilia.  So I changed my example to
how it is now, which is a shame, because I was previously using
"traditional reptiles" as an example of a doubly paraphyletic group,
{Reptilia-Aves,Mammalia} and I no longer have any such example.

Now reading Jamie's comments, I am getting the impression that my
first idea was right, and Mammalia _is_ inside Reptilia after all.  Am
I right?  What's the story with the dinosauricon?

Thanks again,

 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor | <mike@miketaylor.org.uk> | www.miketaylor.org.uk
)_v__/\  "Hoddle had stepped beyond the bounds of Blair's new,
         carefully focus-grouped and concensus-adjusted definition of
         freedom of speech, which is the freedom to say only those
         things which no one else could possibly object to" -- Giles
         Smith.