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Re: Earliest known Dromaeosaurid?



Mike Keesey wrote-

> True; Another possibility, not mentioned in your post, is that
> Dromaeosauridae as traditionally conceived is paraphyletic.
>snip<
> Were this true, all birds would become Dromaeosauridae (and
> Velociraptorinae) using the current definitions!

Yes, that would be an additional problem with the current definitions.  I
didn't mention it because I've only heard of this result in a study by the
AMNH group (I think), which I have no further details on and is currently
unpublished.

> Any thoughts on why the more bird-like ones come out as more derived?

Probably because the taxa in between dromaeosaurids and avians (troodontids
and alvarezsaurids) have basal codings in certain areas (ventrally facing
glenoids, shorter untwisted coracoids, no dorsal ischial processes, etc.),
which makes it most parsimonious for dromaeosaurids to start that way to.
On the other hand, my other phylogeny is the reverse, with dromaeosaurines
derived.  I'm not sure which I support at this point.  I'll have to include
the new characters I developed for my reduced analysis in my major analysis
to see which is better supported.

> It isn't possible that this grouping is due to subadult characters, is it?

Sinornithosaurus is a subadult?  News to me.  Unfortunately, I can't defend
my position with synapomorphies at the moment, as PAUP seems to have erased
itself.  I'll get it installed again soon and present the evidence.

> Much more stable; however, it runs a high risk of being synonymous with
> Deinonychosauria (_Deinonychus_ <-- Neornithes).

The only non-dromaeosaurid deinonychosaur in my phylogeny is
Protarchaeopteryx (and it likes to jump around between that position, basal
paravian and basal segnosaur-oviraptorosaur).  The only other taxa I've
heard of being placed closer to Deinonychus than to birds are troodontids
and Rahonavis.  Thus, by excluding troodontids and Protarchaeopteryx from
the Dromaeosauridae, we retain its traditional composition.

> These have been described as possibly deinonychosaurian or avialan,
> though.

Actually, Britt says they are probably "from a dromaeosaurid or, perhaps,
Marshosaurus".  Teeth are known from Marshosaurus, but I lack details.  I
would think they have the standard "megalosaur" morphology, and thus be
quite different from dromaeosaurids.  The Morrison teeth have high DSDI
ratios, which is a feature currently only known in velociraptorine
dromaeosaurids (whether monophyletic or not).

Mickey Mortimer