Quo vadis, T. rex?

["King, Norm" <nking.ucs@smtp.usi.edu>]

Can someone convince me that tyrannosaurs are maniraptorans?  I know they 
might be, but I'm still skeptical.

A sticking point for me is that tyrannosaurs don't have (am I wrong about 
this?) a semi-lunate carpal--at least their carpals are not shaped that 
way--and it is only POSSIBLE that one was derived from the semi-lunate 
condition, and apparently clear that it was not derived from an 
allosaur-like carpal.  But isn't it also possible that tyrannosaur 
carpals are derived directly from _Compsognathus_ carpals, which we 
unfortunately know almost nothing about?  This MIGHT be a more 
parsimonious hypothesis, since we don't have to assert that tyrannosaur 
carpals passed through a semi-lunate state, for which we have no evidence 
(I say MIGHT, because we know almost nothing about _Compsognathus_ 
carpals, and maybe an assumption is involved here that makes this 
hypothesis just as complicated).  The same comments would apply to 
ornithomiosaurs, if they also lack a semi-lunate carpal (that's right, 
isn't it?).

According to Holtz, tyrannosaurs are grouped with troodonts and 
ornithomimosaurs due to their arctometatarsalian feet (due to this 
largely or entirely[?], once it is assumed they are maniraptors).  This 
can be inferred to indicate they are highly derived maniraptorans, and 
maybe that makes it easier to believe that they once had a semi-lunate 
carpal, then lost it (since they're highly derived).  Primitive 
ornithomimosaurs (e.g., _Harpymimus_) lack the arctometatarsalian 
condition (isn't that right?).  Now, if troodonts are truly maniraptorans 
and have arctometatarsalian feet, and advanced ornithomimosaurs have 
arctometatarsalian feet, but the primitive ornithomimosaurs did not, then 
why is it not possible that troodonts and ornthomimosaurs developed 
arctometatarsalian feet convergently (and, perhaps tyrannosaurs, as 
well)?  

Since ornithomimosaurs also lack a semi-lunate carpal, and developed 
arctometatarsalian feet independently from derived (advanced) 
maniraptorans, perhaps they are not maniraptorans at all.

According to Holtz (J. Paleo., v.68, no. 5, p. 1107), an unambiguous 
synapomorphy of maniraptors (sensu Gautier only?) is a long and slender 
metacarpal III, yet tyrannosaurs have a very short metacarpal III.  Also, 
in maniraptors metacarpal I is one-third or less the length of metacarpal 
II, but that is not what is shown in illusrations of tyrannosaur manus 
("manuses") that I've seen.  Since tyrannosaurs lack these unambiguous 
synapomorphis, and also lack the semi-lunate carpal of the Maniraptora 
sensu Holtz, and we know(?) that some coelurosaurs developed an 
artometatarsalian condition independently of others, I am not convinced 
that tyrannosaurs are maniraptorans.  Coelurosaurs, yes--maniraptorans, 
maybe.  

What do I have wrong, or don't know, that is keeping me from accepting 
the maniraptoran status of _T. rex_?


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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



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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