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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
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
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: email@example.com