Re: fun with ptero diversity

[David Peters <davidrpeters@earthlink.net>]

> Chris Bennett wrote
>
> Is there any reason to think that cladograms can possibly reveal missing
> diversity?  Suppose we consider the bird tree--erase all passerines and we
> would be missing a very important part of bird diversity, yet I suspect that
> the cladogram would look complete, with no evidence that the passerines
> "should" have been there.
>

Dear Chris,

Not sure if this reply was also sent to the dino list. I'll assume so.

I am unqualified to answer your question, Chris, having no experience at all in
bird cladograms. However, IMHO, 'suspecting' an answer before one is produced
can lead to surprises.

But in the meantime, a little research led me to this site on the web where it
appears that no one has yet figured out "The Birds" despite DNA and soft tissue
evidence in abundance:

http://tolweb.org/tree?group=Neornithes&contgroup=Aves

According to the web page author: "Ordinal phylogenies based on morphological
characters have many polytomies deep within them because few derived
morphological characters have been recognized that unite particular avian
orders in sister group relationships."

The cladogram of the neornithes appeared to be one giant polytomy. If someone
has information other than the above and it has appeared on the list, forgive
me, my "blinders" were on. Please send updates on or off-line.

The situation is much improved in pterosaur relationships, with lots of little
bushes, and surprisingly many of the 'baby' pterosaurs give important insights
at the all important basal pterodactyloid point. The babies are a surprisingly
diverse group.

More to Chris's point: There are some pterosaurs, at node bases, that bridge
important morphological differences. If they were missing, or if one major
group seemed to bear little resemblance to other groups, then yes, missing
diversity might be indicated. Other pteros appear at the branch tips and thus
have little to no connection to other groups. Their loss would go unnoticed. So
the choice of the taxon to be excluded is important.

So, are the passerines basal to other forms? And would their loss create a
visible gap? Apparently, at this time, no one can say.

David Peters
St. Louis