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Re: SICB Report



At 09:46 AM 1/18/99 -0600, Chris Brochu wrote:

>Something I've noticed - morphological data sets for a particular group
>usually agree with one another.  Theropods are an exception - this is
>something I've had to adjust to, as in my previous life I was involved
>with a community that was basically producing the same tree.  And I
>think this has more to do with differences in taxon sampling than
>morphological interpretation.

Indeed.  Also, there actually is some pretty strong correspondence within
coelurosaurian topology among some of the latest trees.  Looking at Sereno's
tree (see the 1997 Annual Review paper or the new Neues Jahrbuch), Makovicky
& Sues (in the Amer. Mus. Novitates paper on _Microvenator_), and my own
latest.  In all these analyses, the topology among well sampled coelurosaurs
produces the following:

Ornithomimosauria + (Oviraptorosauria + (Dromaeosauridae + Avialae))

[I do not think it is coincidence that this is also the primary tree
topology within Gauthier's 1986 analysis - Jacques really uncovered
something very important!]

Where the analyses differ is the placement of taxa whose name begins with "t".

In Makovicky & Sues and my own, Therizinosauroidea is the sister group to
Oviraptorosauria; in Sereno's, it's the sister group to Ornithomimosauria.

In Makovicky & Sues and Sereno's, Troodontidae is the sister group to
Dromaeosauridae; in my own, it is the sister group to Ornithomimosauria (but
only a couple of steps out takes it to the sister to droms + birds or to
oviraptorosaurs + therizinosauroids or both).

In Makovicky & Sues', Tyrannosauridae is the sister group to all of the
above; in my own it is closer to Ornithomimosauria (and sister taxon to
Ornithomimosauria + Troodontidae); in Sereno's its the sister group to
Oviaptorosauria + (droms + birds).

So, yes, there is disagreement, but there is also congruence.  In fact,
nobody's finding dramatically different topologies (like tyrannosaurids
closer to _Allosaurus_, or ornithomimosaurs closer to coelophysoids) even
though those results are possible under the data bases being used.

For more, see my talk at the Ostrom Symposium (Arctometatarsalia Revisited:
the problems of homoplasy in reconstructing theropod phylogeny).

Later,

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661