Re: Cladospeak (Mammalia, Crurotarsi)

["Jaime A. Headden" <qilongia@yahoo.com>]

Ken Kinman (kinman@hotmail.com) wrote:

<As for Crurotarsi, I am not saying "it MUST be bad". I am saying the 
synapomorphies supposedly
supporting it as a clade do not appear significant (i.e. not strong), and 
compared to the mammal
synapomorphy, they are downright "weak" (comparatively insignificant). 
Therefore I am saying
Crurotarsi "MIGHT be bad", so I am encouraging people to take a harder look at 
it instead of just
repeating Sereno and Gauthier's synapomorphy lists like they have it all 
figured out already. If
those who plan to defend Ornithodira sensu stricto (contra Dave Peters) plan to 
use Sereno's
Crurotarsi synapomorphies as a given, then I think they may be basing their 
arguments on an
insecure foundation, and perhaps even sliding down a slippery slope of circular 
reasoning. I
assume the pro-"Ornithodira sensu stricto" arguments have not yet been 
expressed on the web, so I
guess we'll just have to wait for the paper (whenever that might be).>

  If Crurotarsi is disbaned because *Ornithosuchus* is knocked out, this says 
nothing of
Psuedosuchia. Also, Crurotarsi as of your operating definition still operates 
on the inclusion of
all other pseudosuchians. This simply implies a refined definition. Such a 
shaky definition of
having about five or six internal specifiers. But, hey, we move on. If 
*Ornithosuchus* goes back
to being closer to dinosaurs versus crocodiles (i.e., sensu Gauthier), this 
does not destabilize
Ornithosuchia or Psuedosuchia ... The PhyloCode advocates making 
feature-dependant names like
Crurotarsi as apomorphy-based clades. Sounds good. But hey ...

  I would like to know what features diagnosing Crurotarsi you feel need to be 
evaluated. You have
obviously looked at some of them to come to this conclusion. I'd like to see 
what you think of
them?
 

  Beleive it or not, there was a thread or two earlier on the validity of 
Ornithodira ...

<I might add that plesiomorphies and convergences are "observed", just as 
synapomorphies are. 
However, assigning these observed characters to a synapomorphy list is in the 
mind of the
beholder, and such lists are created. I just think too many people take it for 
granted that these
are synapomorphies just because Gauthier and Sereno agreed on them (or at least 
most of them). I
might even come to the conclusion that their synapomorphies for Crurotarsi and 
Dinosauria are
strong when taken together, but since noone seems to be willing to say that 
some subset of those
"synapomorphies" are more significant (or stronger) than others, it certainly 
will take me that
much longer to come to a decision.>

  Good. Maybe an evaluation of why you think a synapomorphy is strong or weak 
will come with this.
And an evaluation of what characters do not diagnose Crurotarsi.

<I am reluctant to say who may or may not still regard Ornithosuchids as closer 
to birds than to
crocs (as views change so rapidly sometimes), but I believe Michael Benton 
still favors this
toplology. And I believe Dave Peters also favored this topology (not sure if he 
still does). 
However, I'm not going to rattle off a long list of people who probably still 
favor it, but there
are enough that I think it's still rather iffy which way the ornithosuchids 
will go, and
Crurotarsi could easily end up a synonym of Archosauria. Lewisuchus may be just 
a sign of things
to come.>

  How so? *Lewisuchus* was a conventional thecodont, then was associated with 
lagosuchs and
dinosaurs. It's never been a pseudosuchian or crurotarsan, I believe... If you 
cannot name names
and opinions, then don't offer them. If there's published data, offer it.


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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