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Re: *Utahraptor* and Polyphyly of Recent Dromaeosaurids



Jaime Headden wrote-

>   Arguing for a monophyletic Dromaeosauridae:
>
>   1. fused interdental plates;

Present in Dromaeosaurus, Achillobator, Deinonychus, Velociraptor and
Bambiraptor, but not in Sinornithosaurus.

>   2. lateral frontal process turned at an angle to meet
> postorbital;

Present in Dromaeosaurus and to  lesser degree in Velociraptor, but
Bambiraptor and Sinornithosaurus are similar to troodontids.

>   3. vertical posterior process of the articular posterior to
> the retroarticular process;

I'd like to see evidence of this in taxa besides Dromaeosaurus and
Bagaraatan.

>   4. squamosal bears a lateral ridge from the postorbital to the
> paroccipital process;

Judging by my not-so-clear photocopies of Clark et al. (1994), this seems to
be present in Erlikosaurus.  It is present in Dromaeosaurus, Deinonychus,
Velociraptor and Bambiraptor, as well as Archaeopteryx.  Allosaurus and
Carnotaurus also show this character.

>   5. quadratojugal "T"-shaped, the posterior process about as
> long as the anterior process;

This is present in Dromaeosaurus, Deinonychus, Velociraptor, Bambiraptor and
Sinornithosaurus, but also in Erlikosaurus.

>   6. the prefrontal is fused with the lachrymal, forming a
> "T"-shaped lachrymal (not analogous to the T-shaped lachrymal of
> ornithomimids, whose prefrontal is separate);

This can also be seen in oviraptorosaurs, troodontids and
confuciusornithids.  Dromaeosaurus, Deinonychus and probably
Sinornithosaurus have unfused prefrontals, while Velociraptor and
Bambiraptor show the advanced condition.

>   7. form of the denticles of the teeth;

Not sure what you mean here.  The velociraptorine tooth form is known in
most taxa, but notably lacking in Dromaeosaurus, Achillobator and
Utahraptor.

>   8. dorsal vertebrae with pedunculate parapophyses;

Not examined in most taxa, but also present in Patagonykus and Mononykus.

>   *Sinornithosaurus*, for the most part, appears to be the most
> basal dromaeosaurid. I lacks the pelvic modifications that
> velociraptorines and *Archaeopteryx* share. The large degree of
> birdiness in it are shared by velociraptorines, *Unenlagia*,
> *Rahonavis*, *Archaeopteryx...* and so on. Very funny animal.

Very similar to Microraptor and Archaeopteryx.  The pes has some troodontid
features, like the former.  There are some velociraptorine characters,
others more primitive than dromaeosaurids, and yet others more bird-like.
Other characters are like Bambiraptor and to a lesser degree, Unenlagia and
Rahonavis.  It supports either a paraphyletic Dromaeosauridae with
velociraptorines closer to birds, or a monophyletic Dromaeosauridae with
velociraptorines basally placed.

> *Bambiraptor* is even weirder, but my observations on both these
> are based off the papers, rather than anything I could seriously
> say is a "pers. obs." of the material. The skull exhibits,
> unlike *Sinornithosaurus* but like other "dinobirds" including
> *Archaeopteryx* and pygostylians, a slender jugal below the
> orbit ennervated by extensive foramina, a dorsally bulbous
> braincase, and other features that seem to be indicated by the
> holotype's immaturity.

What?! Sinornithosaurus has a narrower jugal, if the element questionably
identified as jugal by Xu et al. is correctly identified.  The detail isn't
good enough to determine the presence of foramina in Sinornithosaurus.  The
frontal of both species is very similar, Sinornithosaurus having a longer
orbital margin and more extensive supratemporal fossae.  Bambiraptor is a
very good intermediate between Sinornithosaurus and Velociraptor.  The
pelvis has some odd primitive characters, but the pectoral girdle seems more
advanced than most dromaeosaurs.  Some reseblences to Rahonavis and
Unenlagia are also seen.

> *Unenlagia* was suggested by Norell and Makovicky (1999) in
> their second report on *Velociraptor* from Mongolia as being
> similar to dromaeosaurids. This results from the from of the
> femur, vertebrae (pedunculate parapophyses, short transverse
> processes), and some pelvic features (form of the pubic boot,
> form of the pubic apron, extent of the ischiadic symphysis). The
> ischium is strange in its extreme brevity, and seems to be
> similar to other dromaeosaurids more than it is to such like
> *Rahonavis* (as reflected by Forster et al., 1998),
> *Bambiraptor* (Burnham et al., 2000), and *Sinornithosaurus* (Xu
> et al., 2000).

This taxon is the jumpiest dromaeosaur included in my analysis.  The
dromaeosaurid synapomorphies are not very convincing, so it sometimes finds
itself next to Archaeopteryx and Rahonavis, regardless of where
dromaeosaurids are.  Besides these taxa, it resembles Sinornithosaurus and
Bambiraptor closely.  Some pelvic characters are suspiciously like
Achillobator though, which may indicate dromaeosaurine relations.

> This all suggests a gradational
> arrangement, and my preliminary observations are that
> Dromaeosauridae is monophyletic, but that *Sinornithosaurus* and
> the rest are closer to birds than *Velociraptor* is, thus are
> avialian; then we find *Sinornithosaurus*, and *Bambiraptor*,
> and apparently *Unenlagia*, then we get *Rahonavis*, then Aves.

As you can tell from my previous comments, I agree.  However, the issue of
whether Archaeopteryx is closer to neornithines or not affects the
interpretation of Sinornithosaurus and other "dino-birds" as avialan or
deinonychosaurian.

Mickey Mortimer