Re: T-Tip

[Nick Longrich <nrlongri@midway.uchicago.edu>]

> I'm not even sure about Sinosauropteryx as an Compsognathidae, but the
>argument
>about the fingers is right. It just was the point that brought me to that
>idea,
>together with the long distance in time between Compsognathus and the
>tyrannosaurids, I knew.

        This is a crucial point indeed. How do we know that Sinosauropteryx
and Compsognathus are related? *No one has done a cladistic study to test
this hypothesis.* In my opinion, for what it's worth, the character
evidence is not exactly extensive or well-documented, and some of these are
just tooth characters, which I think in general have little weight for
Coelurosauria.
        While yes, Coelurosauria is *technically* defined by phylogeny and
not size, I think you may be closer to correct than some people think about
how it ends up being*practically defined*. I mean, probably the first thing
many people do confronted with a small theropod is think "Coelurosaur", not
"torvosaur" or "allosaur". And the sad truth is that sometimes we don't go
back and adequately test our initial assumptions if we find a few pieces of
evidence that initially would seem to support them, or if people tell us
more or less what we expect to hear, or if the conclusions seem to be
coming from authority. Just because it's published in Science or Nature
doesn't mean it's true. Look how much our ideas on Caudipteryx have changed
since that animal was first published.
        Based on gestalt, personally I'd suspect that Sinosauropteryx- the
two animals described by Chen et al.- falls nearer things like Allosaurus
than Compsognathus. From what I can tell of its build, for such a small
animal it is remarkably robust- the fibula seems very large (contrast that
to the extremely slender on in Compsognathus), the tibia short compared to
the femur, and the forelimbs seem unusually stout as well. The neck is
quite short. But we need more evidence... laid out in a hierarchical
phylogenetic scheme (i.e. a cladistic study). Until then, I think it is
unjustified to at this point conclude Sinosauropteryx and Compsognathus are
closely related, given the massive gaps in our understanding of theropods
in general, coelurosaurs in particular, and Sinosauropteryx and
Compsognathus especially.