[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Theropod phylogenies
----- Original Message -----
From: "Richard Forrest" <firstname.lastname@example.org>
Sent: Saturday, February 01, 2003 2:34 PM
> As I understand it, sorting out the relationships of modern birds based on
> morphology alone is tricky, and the advent of firstly molecular data, and
> more recently DNA analysis has led to some extensive revision of their
> relationships. The fundamental problem is that many features in birds,
> especially in their skeletal morphology, are strongly convergent.
To me it looks like most of the problem is due to how the morphological
analyses of birds are done. Some look at the shape of the stapes. Others
take the quadrate for this. Others look at leg muscles (leading to parrots
and mousebirds as sistergroups, against much tradition). Others look at the
shape of the brain (for example, the Mlíkovský pdf says that traditional
Falconiformes are polyphyletic even without the New World vultures). And so
on. Apparently nobody looks at everything at once. I don't know of an
analysis with 20 taxa and 200 or 400 characters like is regularly done for
more basal theropods.
The rest of the problem is due to the scrappy pre-Eocene northern
and pre-er... Miocene or so southern fossil record. And maybe to an
explosive radiation after the K-T.
The molecular trees have remarkably little resolution within
Neognathae. I say more genes and longer sequences...
> It seems to be accepted without question that the various
> cladograms produced exploring these relationships are true phylogenies.
They are phylogenetic hypotheses, the results of (hopefully) scientific
analyses. Imagine every line on a cladogram is stippled. :-)
> especially if they are so closely related to
> modern birds that some contributors to this site make no distinction?
To birds as a whole, not to Neornithes, if by "closely related" you mean
distance along the cladogram's lines.