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Re: Status of _Utahraptor_?



Look like we're delving into dromaeosaurs yet again.

Larry Dunn wrote-

> I've recently overheard that the status of
> _Utahraptor_ may be in doubt.  Is that true?  If so,
> why?

And Jordan Mallon wrote-

> Well, while on the subject of _Utahraptor_, and taking into account that
it
> may be a valid genera, have there been any further developments on its
> affinities within the Dromaeosauridae?  Last I heard, its placement within
> the dromaeosaurinae was still being questioned.

As Tim Williams has pointed out, the supposed questionable status can be
attributed to Burnham et al. (2000).  I personally believe Utahraptor is
both valid and deinonychosaurian, although I'm not sure about any exact
relations among the Eumaniraptora at this point.  This would have to be
resolved before Utahraptor could be placed anywhere.  The teeth are
plesiomorphically not velociraptorine, which resembles Dromaeosaurus and
Achillobator.  The last two premaxillary teeth are smallest, like
Velociraptor and Sinornithosaurus (this is *not known* in Dromaeosaurus, so
cannot be used to place the taxon in the "Velociraptorinae").  The caudal
vertebrae seem more similar to Deinonychus than Achillobator.  There's too
many details to comment on here, perhaps I'll write "Details on Utahraptor"
sometime....

Then George Olshevsky wrote-

> Perhaps the closest relative of Dromaeosaurus is Mongolia's Bagaraatan,
but since the
> only comparable elements are dentaries, this is a very tentative guess.
I've been rereading > Phil Currie's (1995) description of Dromaeosaurus and
let
> me tell you the family Dromaeosauridae is in deep trouble. Almost all the
> theropods everyone has been calling "dromaeosaurids" probably aren't; they
> should be referred to as "velociraptorids" instead (with Velociraptorinae
> raised to family level as Velociraptoridae).

Quite intriguing.  Dromaeosaurus differs in having- a more pointed anterior
dentary; more robust and straighter dentary ramus; fused interdental plates;
single surangular foramen; less pronounced preglenoid process; longer
articular region of jaw; shorter and broader splenial rounded anteriorly;
pedal phalanx II-2 slender with shallowly grooved articular surface.  The
lack of fused interdental plates or specializations of pedal digit II
suggest Bagaraatan is not a dromaeosaur.
I agree that dromaeosaurids are in trouble, but for a different reason.  Too
many people have gotten used to the dromaeosaurine vs. velociraptorine
dichotomy.  There is actually a rather well-supported sequence of
dromaeosaurs that get morphologically more bird-like
(Dromaeosaurus/Achillobator/Adasaurus, Deinonychus, Velociraptor,
Bambiraptor, Sinornithosaurus/Microraptor).  Utahraptor may fit between
Dromaeosaurus and Deinonychus, while Unenlagia could go at either end.  The
questions are- are they paraphyletic in respect to birds, and which side is
most derived?  My analysis suggests "no" and
"Dromaeosaurus/Achillobator/Adasaurus", but could easily be wrong.

Finally Thomas Holtz wrote-

> The original description also includes a discussion of various foot
elements
> found with the skull: these have never been illustrated, if memory serves.

These are indeed illustrated (fig. 14 and 15), along with a pedal ungual now
thought to belong to Saurornitholestes.  Nearly identical to Deinonychus
besides the robust phalanx II-2, which is like that of Adasaurus and
Achillobator.

Mickey Mortimer