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Re: Reflections on Recent "Dromaeosaurs"



Good discussion Jaime.  There's way too much information to go through for
me to present my own opinion of dromaeosaur phylogeny, but I do have some
things to add.

>   It is becoming more and more clear to me that the
> Dromaeosauridae, sensu Holtz (1995) and Padian et al.
> (1999), is polyphyletic.

It seems that way on first glance, but my analysis continues to support
their monophyly.  This is, of course, not final as many more characters need
to be added.

>   Velociraptorine dromies tend to share more features
> of the braincase, skull, and pelvis, with birds than
> less "advanced" dromaeosaurs ("dromaeosaurines").

What taxa besides Dromaeosaurus do you include in the Dromaeosaurinae?
Adasaurus was considered a dromaeosaurine by Paul (1988), but the second
pedal ungual wasn't necessarily reduced in Dromaeosaurus and skull material
for Adasaurus is undescribed.  Utahraptor was originally placed in the
Dromaeosaurinae, but Currie (1995) thought it most probably a
velociraptorine.  The point is that since Dromaeosaurus is the only
Dromaeosaurine at present, only skull material (and some pedal elements) can
be compared to velociraptorines at present.  Dromaeosaurus would seem to
have plesiomorphic characters not only compared to velociraptorines, but
also compared to other maniraptorans like therizinosaurs, oviraptorosaurs
and troodontids.  This suggests that at least some of it's primitive
characters may in fact be reversals, possibly related to it's convergence on
tyrannosaurs.

The
> original grouping of these animals based on the
> structure of the skull and lower jaw presented a
> robust, deep skulled Dromaeosaurinae and a
> shallow-skulled, narrow, birdy Velociraptorinae (Paul,
> 1988a,b);

Actually, my analyses don't even support a monophyletic Velociraptorinae.
Many of the usual "velociraptorine" features aren't found in all
"velociraptorines".  For instance, Deinonychus's premaxillary teeth are all
subequal in size (Ostrom 1969) and only Velociraptor has depressed nasals
(which may be present in Dromaeosaurus for all we know).  New Deinonychus
material makes it look more like Dromaeosaurus than illustrated by Paul.
The only really good velociraptorine synapomorphy I know is the presence of
teeth with posterior serrations much larger than anterior serrations.

Kirkland et al. (1993) presented a likewise
> deep skulled animal older than the velociraptorine
> *Deinonychus*, *Utahraptor*, but lack of skeletal
> details have made this animal less distinguishable
> than is liked in a taxonomic analysis.

I concur.  I would need the original paper for a detailed comparison, but
the prezygopophyses are elongate as in other dromaeosaurids and the second
premaxillary tooth is the largest as in Velociraptor and Sinornithosaurus.
How can Currie (1995) claim that the second premaxillary tooth in
Dromaeosaurus is subequal to the others if only teeth three and four are
known anyway?

Bambi itself shares a
> deeply curved dentary and elongate orbit with
> velociraptorines, but a pelvis morphology similar to
> *Unenlagia* and *Rahonavis* (Buchholz, comm. to the
> list, 1998, 1999; pers. obs.) that suggest that, not
> only are Unen and Rahona part of the commonly
> considered "dromie" grouping, Bambi is plesiomorphic
> of the Dromaeosauridae and possibly lies closer to
> birds than to velociraptorines.

What besides the dorsally projected pubic foot (in Unenlagia) and
proximodorsal ischial process (which is also present in avians) does
Bambiraptor share with Unenlagia and Rahonavis?  Although much has been made
of new dromaeosaurid synapomorphies in Unenlagia noted by Norel and
Makovicky (1999), not much actual evidence is put forth.  Stalked
parapophyses are also present in mononykines and their presence is uncertain
in Rahonavis and Archaeopteryx.  Expanded dorsal neural spines are also
present in troodontids and posterior dorsal pleurocoels are also present in
Beipiaosaurus and oviraptorosaurs.  Unenlagia and Rahonavis may be
dromaeosaurids, but more characters have to be put forth before this can be
justified.  For now, they go slightly closer to Aves in my trees.

>   Additionally, *Achillobator* ......

Achillobator, despite all of it's non-dromaeosaurid characters, still groups
with dromaeosaurids in my analyses.  Note the fused interdental plates,
reduced anterior serrations and enlarged pedal ungual II along with the
caudal and ilial features you mentioned.  Also, the scapulacoracoid is very
similar to Deinonychus, which lacks the twisted, elongate coracoid with
lateral glenoid fossa found in Sinornithosaurus, Velociraptor, Bambiraptor,
Unenlagia and Rahonavis (coracoid unknown in last two genera, but glenoid
still laterally directed).

>   *Bambiraptor* and *Sinornithosaurus* have another
> feature that is not mentioned in Burnham et al.:
> lateral ornamentation of the maxillary antorbital
> fossa by pnuematic fossae, seen also in
> sinraptorine/id allosaurs (Currie and Zhao, 1993).
> This might be construed as either a synapomorphy of
> the two, as a plesiomorphy of all dromaeosaurs
> reversed in more advanced forms, or a homoplasy.

Good eye.  I'll add this to my character list.

>   *Bambiraptor* is also well united with bird-trend
> dromies on the basis of what Burnham et al. suggest is
> a triosseal canal, with separation of the coracoid
> dorsal margin from the acromion by a concavity of the
> edge, and extreme retroversion of the coracoid from
> the long axis of the scapula, which is lacking in
> velociraptorines, and relatively more "avian" than
> *Sinornithosaurus* (Burnham et al., 2000; Xu et al.,
> 1999).

Velociraptor also has a depression separating the acromion from the coracoid
body, as seen in Norell and Makovicky (1999).  In fact, the proximodorsal
ischial process and very elongate sterna are the only features that would
suggest Bambiraptor is closer to birds than to Velociraptor.

This
> is the bulk of Burnham et al.'s differentiation, so
> I'm not too willing to trust it, but it seems a
> likelyhood. At worst, Bambi is a unique "species," if
> not a genus.

I'm rather cautious of the differentiation of Bambiraptor from
Saurornitholestes as well, based as it is only on frontal proportions.  What
do we do with all of the "Saurornitholestes" material now?  Much of it
consists of teeth, which are not very well described in Bambiraptor.  There
needs to be a detailed comparison done of Bambiraptor with material
previously referred to Saurornitholestes to determine any differences.

Mickey Mortimer