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Re: Tyrannosaurs with leathery skin, etc.



Nick Longrich wrote-

>Sinosauropteryx looks to be more primitive than tyrannosaurs or
>ornithomimids, maybe even further from birds than Allosaurus (it is one
>primitive sucker), . . .

I agree that it is more primitive than ornithomimids, and possibly more so
than tyrannosaurs, but several coelurosaur synapomorphies are present
showing it is more advanced than Allosaurus and other carnosaurs.
- amphicoelous cervical vertebrae
- slender third metacarpal
- fourth metacarpal absent (convergent in Allosaurus)
- dorsal margin of ilium slopes caudoventrally
- obturator process placed more than 25% down the ischial shaft
- triangular obturator process
- ischium reduced in length compared to pubis

>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.

Although Sinornithoides lacks anterior serrations on some teeth, I am not
aware of any troodontids that lack serrations entirely.  Actually, the
compsognathid synapomorphy used was "unserrated premaxillary teeth, but
serrated maxillary teeth".  This is not very widespread, occuring only in
Sinosauropteryx, Compsognathus, "aublysodonts" and Sinornithosaurus among
coelurosaurs (and only in coelophysids outside of this clade).

> 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.

Again, the synapomorphy used was "shaft diameter of manual phalanx I-1
greater than that of radius".  Although the manus is disarticulated in
Compsognathus, examination of the type shows at least three of the manual
phalanges are thicker than the radius.  This also known in Ingenia,
Patagonykus and mononykines, but that's about it.

> 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.

The synapomorphy is "prominent obturator process", not "obturator process
present".  Although not visible in the paper, personal examination and
photographs of NIGP 127587 show it to be present.  The obturator process in
Compsognathus is rather large, this is presumedly what the synapomorphy
refers to.

> Which leaves us with fan-shaped neural spines. Unfortunately, these
>haven't been illustrated for Sinosauropteryx.

They may not have been illustrated, but they are specifically referred to.
If we could only trust what was illustrated, those of us unable to examine
specimens would have a lot more ?'s in our matrices.


"Limited anterior expansion of pubic boot" was also cited in the paper.
This is also found in Coelurus, Calamospondylus, Scipionyx  and
eumaniraptorans, however.

>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.

There have to be some differences between taxa.  The chevrons aren't that
different, only shorter in Sinosauropteryx.  The pubic boot is about the
same length as Scipionyx, and longer than Sinornithoides, Sinornithosaurus,
Ingenia and mononykines.  The chevrons of Compsognathus also never expand,
as shown in the MNHN specimen.  I don't know where you came up with 47
transverse processes.  The paper states at least four pairs were present,
and other caudals only have low bumps.  Besides, the lack of transverse
processes is an autapomorphy of Compsognathus, and as such doesn't help
determine relationships.

Mickey Mortimer