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Re: Quo vadis, T. rex



Nick Pharris responded (02/01/96; 2:19p) to several points of my querry.  
I'm obviously struggling with some of these concepts, and appreciate the 
help.  I still have questions:

About tyrannosaurs having a degenerate semi-lunate carpal:

>There is only one really well-preserved tyrannosaurid carpus that I know 

>of, and that is from _Albertosaurus_ (?).  It shows five carpals, one of 

>which is evidently a degenerate semilunate.

Does "evidently" mean that one really looks like a degenerate semi-lunate 
carpal, or is it evidently so because it must be to fit the 
classification?

About tyrannosaur carpals coming straight from _Compsognathus_:

>Why are you suggesting this?  Does it have anything to do with the 
>didactyl manus in that genus? (which, incidentally, has a reconsturcted 
>phalangial formula of 2,3,3,0,0, more "derived" than any tyrannosaur).  
>Didactyly is pretty easy to develop in parallel.

No.  Actually, I have seen the claim that the manus of _Compsognathus_ is 
too poorly preserved (I don't have a reference handy for that one) to say 
it is unquestionably didactyl, although I realize that Ostrom has looked 
at it recently and pronounced it so.  I was concerned about reversals of 
characters reported by Holtz.  The Maniraptora developed flexed cervical 
zygapophyses, but this was reversed at Arctometatarsalia (so, that 
character considered alone [ok, I know!], we go back to the next step 
before Maniraptora, which "picks up" -Compsognathus_.  Then, at the next 
node beyond Arctometatarsalia, but before we get to the tyrannosaurs, 
three more characters are reversed, including another unambiguous 
synapomorphy of maniraptorans--posterodorsal margin of ilium curved 
ventrally in lateral view.  One of the other reversals at the node beyond 
Arctometatarsalia is for a synapomorphy at the next node beyond 
Maniraptora.  I didn't "grow up" with cladistics, but rather with 
numerical taxonomy, back in the late 60's, so maybe I still don't have 
command of cladistic principles.  But I thought we should be suspicious 
of reversals.  Am I wrong on that?  If I'm right, why aren't we 
suspicious of these?  It seems that to make tyrannosaurs and 
ornithomimosaurs more derived than maniraptors, we have to undo a lot. 

About arctometatarsaian feet:

>> According to Holtz, tyrannosaurs are grouped with troodonts and 
>> ornithomimosaurs due to their arctometatarsalian feet (due to this 
>> largely or entirely[?], 

>Nope.  Tyrannosaurs also show a good many more maniraptoran 
>autapomorphies, particularly in the skull.

If we undo all of those characters--like assume they never developed in 
the first place--the arctometatarsalian feet certainly become much more 
important (ok, I've left out one group of synapomorphies--at the node 
just before Arctometatarsalia); "entirely" was too strong a word.

>In fact, tyrannos show innovations in foot structure and neural pathways 

>strongly indicating that they are closer to birds than dromaeosaurs are, 

>and maybe even closer than _Archaeopteryx_!

You mean Bakker was right???

About primitive ornithomimosaurs lacking arctometatarsalian feet:

>_Garudimimus_ has been shown to be fully arctometatarsalian, and 
>_Harpymimus_ is apparently very poorly preserved.  It is also more 
>primitive in the hand than the much earlier _Pelecanimimus_, and this, 
>along with some other features, including the enlarged preacetabular 
>blade of the ilium, suggests to me that this genus may not be an 
>ornithomimosaur at all, but possibly a relative of the oviraptorosaurs.

Wait a minute!  Why is this counter example invalid?  If it's more 
primitive in hand, why can't it also be more primitive of foot, and 
legitimately so?  Sounds like Johnny Cochran--if it doesn't fit, it's not 
legit!  ;-)

About a short/long metacarpal III in tyrannosaurs:

>It was as long as metacarpal II and quite slender.

What should my authority (reference) be for tyrannosaur metacarpals?



*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu