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Re: Valley of the T. rex, Raptor Red, and Maniraptoran Tyrannosaurs


Nicholas,
As you grow older and more experienced, I think you'll find that latching onto one or two characters can often be very deceiving. Convergence has probably fooled every systematist that as ever lived (even the greatest ones) at various times, and it is especially rampant among coelurosaurs.
Not that I am in favor of the other extreme of weighting all characters perfectly equally in the final analysis. The more characters the better, but ultimately I believe that the best analyses result from some type of weighting (whether some characters are combined or separated, judged more likely to be subject to convergence, etc.). No particular character should be given too much weight (such as the semilunate), but that does not mean all should be given the same weight either.
How to balance these is the tricky part. And also remember that it may be difficult to distinguish something like "semi-lunate degenerating" from "semi-lunate developing", not to mention multiple independent occurences of either. That is what makes groups like these so challenging to systematists. Best of luck.
-----Cheers, Ken
P.S. I personally think Compsognathus or Ornitholestes are more likely to be primitive tyrannosaurs than Coelurus, but until we have more intermediate fossils, noone can know with any degree of certainty.
*******************************************
From: "Mickey Mortimer" <Mickey_Mortimer11@msn.com>
Reply-To: Mickey_Mortimer11@msn.com
To: <dinosaur@usc.edu>
Subject: Re: Valley of the T. rex, Raptor Red, and Maniraptoran Tyrannosaurs
Date: Thu, 20 Sep 2001 20:05:26 -0700

Nicholas Gardner wrote-

>      `--Tyrannoraptora (T1)
>         |--Coelurus
>         `--Tyrannosauroidea (T2)
>            |--Stokesosaurus
>            `--+==(T3)
>               |--Eotyrannus
>               |--Itemirus
>               `--Tyrannosauridae
>                  |--Basal Tyrannosaurids
>                  `--+--Albertosaurinae
>                     `--Tyrannosaurinae
>                        |--Daspletosaurus
>                        `--+--Tarbosaurus
>                           `--Tyrannosaurus
>                              |?-"T." megagracilis (Dinotyrannus)
>                              |?-"T." lancensis (Nanotyrannus)
>                              `--T. rex
>
> (T1) semi-lunate carpal degenerates.
> (T2) tyrannosaur design appears and arctomet begins
> (T3) arctomet developed, specialized braincase features, etc.
>
> Anyone want to comment?

Mike Keesey covered the main points, but I have some things to add.
How can you place Stokesosaurus closer to tyrannosaurids than Coelurus based
on "tyrannosaur design appears" and "arctomet begins"? The first is
extremely vague to the point of being an invalid character. The second is
not only vague, but is unknown in Stokesosaurus, Eotyrannus and Itemirus. A
similar criticism could be made of your "arctomet developed" character
diagnosing Eotyrannus and Itemirus, but not Stokesosaurus. You must also
specify which "specialized braincase features" diagnose this group. These
would be interesting to hear as Eotyrannus' braincase isn't known and that
of Itemirus isn't any closer to tyrannosaurids' than Stokesosaurus' is, as
far as I know. But my knowledge of braincase anatomy is limited. Tom Holtz
would be able to comment on these tyrannosaurian technicalities better than
I could.

Mickey Mortimer



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