[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Re: Quo vadis, T. rex
>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
There is a big flat degenerate distal carpal, which covers the base of mcI &
mcII. It could either be a degenerate semilunate carpal block, or a
degenerate fusion of the distal carpals in the homologous position in other
tetanurines (Allosaurus, for example).
>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.
Having seen the casts of the specimens, it looks like someone took a shotgun
to its hands and blew them up! Gauthier, who has seen the real things, is
equally unconvinced of the didactyly. I think it is a distinct possibility,
> 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.
Suspicious about reversals? I've got to get that "reversals happen" bumper
Incidentally, with elmisaurs and oviraptorids over on the Maniraptora vera
side, many of the previous "reversals" disappear.
>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.
If you run the dataset without those cranial characters, tyrannosaurs fall
back to basal coelurosaurs. Same with the arctomet feet. "Entirely" is 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???
I remain unconvinced of such a position. I am among the last of the people
on this net, it seems, who believes that dromaeosaurids are the sister group
to the Archie + later bird clade...
>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
There are questions as to the ornithomimosaur nature of the really scrappy
Harpymimus type. I still think it is an ornithomimosaur, myself.
Thomas R. Holtz, Jr.
Dept. of Geology
University of Maryland
College Park, MD 20742