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

Re: Postorbital processes (& weighting??)

David,
Need to get some things cleared up here. {Sinornis + Passer} = Euornithes (not Ornithothoraces).
Ornithothoraces is presently defined as {Iberomesornis + Passer}. David asked in his original post if there are any "other ornithothoracines except confuciusornithids" with the process. This phrase seemed to imply he believed confuciusornithids to be ornithothoracines (making the latter equivalent to Pygostylia). This didn't surprised me since some phylogenies would make Ornithothoraces even more inclusive than Pygostylia. So just to clarify, I now assume David meant to say "other pygostylians except confuciusornithids".
But my position will still be pretty much the same. I would not be surprised if the said process was lost independently three, four, or even more times. Multiple losses (even it takes more steps) can be more "parsimonious" if a reversal (reacquisition) is very difficult (that's where function could be important).
Of course, that means I am suggesting some possible "character weighting" might be warranted, and I guess some of the strict cladists will want to thrash me for doing that. So it goes. But equal weighting and puritanical parsimony aren't always going to give you the correct answer.
-------- Ken Kinman
****************************************** 
From: "David Marjanovic" <david.marjanovic@gmx.at>
Reply-To: david.marjanovic@gmx.at
To: "The Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: Re: Postorbital processes on jugals
Date: Sun, 16 Dec 2001 22:21:42 +0100

> Assuming that the said processes have only been lost in mononykines and the "non-confuciusornithid ornithothoraceans"

Pygostylians. Pygostylia = {*Confuciusornis* + *Passer*}; Ornithothoraces = {*Sinornis* + *Passer*}.

> (mercy, how about that for a
> phrase to torture the speaker's mouth and the listener's brain)

Let's give it a name :-)

> ---- why
> would a single loss (plus a reversal) be preferable to two independent
> losses?
> [...]
> Both scenarios require two steps,

That's it. None is a priori preferable. If there is a bird in the above
clade that has the process then 2 losses are definitely more parsimonious.
If there is none, but if there is a non-pygostylian metornithine that also
lacks the process, then a reversal is definitely more parsimonious.
Candidates for the latter position exist, but none has a skull. Therefore
I'm asking about the former position.

>      I guess it depends on what the function of the process is, but off
> hand, it seems like two independent losses might be more likely than one
> loss and a reversal.

Why?



_________________________________________________________________
Chat with friends online, try MSN Messenger: http://messenger.msn.com