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Re: T. rex and the Coelurosauria



>In response to Dr. Holtz's invitation for questions on theropod 
>systematics... coincidentally earlier today I was looking through a back 
>issue of _The Dinosaur Report_ published by the Dinosaur Society and came 
>across an article by Dr. Holtz which questioned whether Tyrannosaurus 
>belongs to the carnosauria or the coelurosauria. I don't have the article 
>at hand, but (correct me if I'm wrong, Tom) the gist of it was that T. 
>rex really has more in common with the coelurosauria. If this is the 
>case, would it be correct to say that T. rex is more closely related to 
>Coelophysis than Allosaurus?
>

[Watch out kiddies, this could be a long one if I don't restrain myself...
;-)]

Okay, first off, Coelophysis is no longer...  Hmm, I'll try this tact instead:
Carnosauria and Coelurosauria were names invented by Friedrich von Huene in
the 1910s and 1920s.  He regarded the former as composed of Allosaurus and
Megalosaurus, and the latter containing Ornitholestes, Coelurus, a lineage
formed of Coelophysis and Ceratosaurus (!) and a lineage formed of
Ornithomimidae and Tyrannosauridae (!!!).  Had people followed up on this,
Jacques Gauthier, myself, and others would have somewhat shorter
bibliographies to our names, but instead...

Through the influence primarily of the American Museum and H.F. Osborn and
his followers, the theropods were divided into two groups primarily on
size-based features.  Thus, the Carnosauria included all the large forms
(moving Ceratosaurs and Tyrannosauridae into Carnosauria) and Coelurosauria
all the rest.  This is the state of affairs in which the last few generations
of dinosaur fans were raised.

Interest in theropod systematics was rekindled by John Ostrom's work on the
origin of birds, and made a major leap forward with the 1986 publication of
Jacques Gauthier's "Saurischian Monophyly and the Origin of Birds", in which
he recognized (on the basis of shared derived characters) the following
phylogeny of theropods:  Ceratosaurus and Coelophysis and their relatives
(Sarcosaurus, Syntarsus, Dilphosaurus, etc.) shared a more recent common
ancestor with each other than either did with Allosaurus, Ornitholestes,
birds, etc.  He applied an old Marsh name, Ceratosauria, to this lineage
(and additional work by Gauthier and this net's own Tim Rowe, as well as
some important Argentine workers, have helped us to understand the
relationships within the Ceratosauria).  So, Coelophysis and Ceratosaurus
were neither carnosaurs nor coelurosaurs, but rather ceratosaurs. The remaning
theropods were placed by Gauthier in the Tetanurae, which itself was divided
into Carnosauria (Allosaurus, "megalosaurs", and the Tyrannosauridae) and
Coelurosauria.

This was the state of affairs when I got to work on my own research (okay, I
left out publication of Greg Paul's Predatory Dinosaurs of the World and a
few other major works, but I'm trying to keep this short).  My own work
(coinciding with independant research by workers in the U.S., Canada,
Argentina, Spain, and elsewhere) showed that, by parsimony analysis,
tyrannosaurids share a more recent common ancestor with dinosaurs such as
Ornitholestes, Ornithomimidae, Troodontidae, Dromaeosauridae, and birds than
with Allosaurus, and therefore were *by definition* coelurosaurs.  There is
disagreement as to the exact position of the tyrannosaurids within the
coelurosaurs (Sereno and Perez-Moreno think they're the sister group to the
Ornithomimid-Maniraptoran clade, I and Currie think they're closer to
ornithomimids and troodontids than to dromaeosaurds, etc.), but most agree
that tyrannosaurids share a more recent common ancestor with birds than with
Allosaurus.

So, to make a long story short (too late! ;-) ), Tyrannosaurus is actually
more closely related to Allosaurus than to Coelophysis, but is more closely
related to Velociraptor than it is to Allosaurus.

Hope that answers the question,

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
Colege Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084