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Re: Earliest known Dromaeosaurid?

On Sun, 19 Nov 2000, Mickey_Mortimer wrote:

> The issue of assigning taxa to the Dromaeosauridae or just to the
> Deinonychosauria is very complex. First, we must have a dromaeosaur
> phylogeny to work with so we know what taxa fall into the (Dromaeosaurus +
> Velociraptor) group.

True; Another possibility, not mentioned in your post, is that
Dromaeosauridae as traditionally conceived is paraphyletic. I've heard of
cladograms like this:

  `--+--Deinonychosauria *

* same as traditional Velociraptorinae in terms of content

Were this true, all birds would become Dromaeosauridae (and
Velociraptorinae) using the current definitions!

> My major analysis finds Achillobator and Dromaeosaurus at the base,
> with Deinonychus, Velociraptor, Unenlagia, Bambiraptor and
> Sinornithosaurus branching off later in that order.

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

[alternate hypothesis snipped]

> Since no phylogeny is the obvious best choice right now (and the only
> agreed upon clades in both of my phylogenies are Bambiraptor +
> Sinornithosaurus

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

> and the dromaeosaur group as a whole), the only taxa definately in the
> (Dromaeosaurus + Velociraptor) group (and thus definately
> dromaeosaurids) are Dromaeosaurus and Velociraptor!


> I suppose Unenlagia is always in the
> (Dromaeosaurus + Velociraptor) group as well, how odd.

Yes, since others have placed it in Avialae.

> The phylogenetic definition was made assuming that the basics of
> dromaeosaurid phylogeny were known, but future discoveries have proven
> that to be anything but the truth. Because of this, I recommend we
> keep a loose definition of Dromaeosauridae until a major phylogenetic
> study is published. I personally think a stem-based definition is much
> better at this point (everything closer to Dromaeosaurus than to
> Protarchaeopteryx, Troodon or Neornithes).

Much more stable; however, it runs a high risk of being synonymous with
Deinonychosauria (_Deinonychus_ <-- Neornithes). This definition works
well where the other one doesn't (i.e., if Troodontidae are
Deinonychosauria, or if _Dromaeosaurus_ falls outside Eumaniraptora). It's
difficult to think of one that works well in all phylogenies. Perhaps, for
that reason, it should be left undefined for now.

> In any case, to address Mike's question, the Portuguese specimens can be
> assigned to the Dromaeosaurinae and Velociraptorinae under the standard
> phylogeny, so these would presumedly qualify as true dromaeosaurids.

Awesome! Is Feduccia getting this? :)

> Also, the Morrison specimens from Colorado described by Britt (1991)
> have velociraptorine serration morphology.

These have been described as possibly deinonychosaurian or avialan,

Thanks for the detailed response. (Looking forward to another.)
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