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RE: Tyrannosaurs with leathery skin, etc.



>>Sinosauropteryx looks to be more primitive than tyrannosaurs or
>>ornithomimids, maybe even further from birds than Allosaurus (it is one
>>primitive sucker), this would still be a considerable subset of the
>
>So does this mean that S.s.pteryx is a basal tetanurine? has the
>relationship with the European Compsognathus been confirmed? It is
>superficial similar but methinks it has several primitive features.

As I understand it, the evidence for compsognathid affinities rests on the
following features:
        -enlarged first digit
        -unserrated premaxillaries, anteriorly unserrated maxillaries
        -obturator process of the ischium
        -fan shaped neural spines


        Which is maybe five or four characters depending on how you want to
code the teeth. Now, I don't think I would have to argue too hard to
convince people that tooth serration is a damn lousy character. Some
troodonts have restricted anterior serration, I think some lack anterior
tooth serration, and some have no serration on any of the teeth. If I
recall, the Chinese dromaeosaur lacks serration on the premaxillaries. So
we are seeing intra-family variation, so it seems like a highly homoplastic
character and likely varied depending on whether the animal was a large or
small game hunter.
        I don't know where the enlarged first digit thing comes from. Last
I checked, nobody had published anything showing convincingly what the
various hand bones of Compsognathus were, and the hand bones and arms seem
rather slender compared to the very robust arms of Sinosauropteryx.
        An obturator process of the ischium is found in all kinds of
things, but it would put it above things like torvosaurs if I recall(?). I
can't make one out in my photocopied version of the paper, though.
        Which leaves us with fan-shaped neural spines. Unfortunately, these
haven't been illustrated for Sinosauropteryx.

        Maybe they are related. But we haven't been *shown* a single
convincing synapomorphy between the two, nor have we seen the animals put
in a phylogenetic context, so one doesn't feel particularly compelled to
believe that they are. My gut feeling- based on phenetic, rather than
phylogenetic grounds (that is, overall similarity, rather than derived
similarity) is that they aren't. Sinosauropteryx has these short, powerful
forelimbs, a shorter neck, different chevrons. It appears to have a very
short pubic boot, unlike the long one seen in most avetheropods and
Compsognathus. It definitely looks more primitive than a maniraptoriforme
or tyrannosaur- the chevrons never turn into skid-chevrons, and the
transverse processes are still out there on caudal 27. If it sort of looks
like Compsognathus- well, in a lot of ways, theropods all look the same
(Except for tyrannosaurs of course, Tom;). I am sure, however, that when
Curry gets done working on it, we will all know a lot more.

        -N