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Re: news from dino central
David Marjanovic wrote-
> > (Tyrann (Nedcolb (Ornithol (Compsog ((Coelur, Scipio) (Ornithom (Nqweb,
> > others))))))).
> Seems like my knowledge is lagging behind a bit or two -- I thought
> *Nedcolbertia* was close to *Ornitholestes*?
> How have tyrannosaurs wound up so far down, compsognathids above
> *Ornitholestes*, and *Nqwebasaurus* so far up?
> What unites *Coelurus* and *Scipionyx* (well, I'm glad someone has found
> _some_ position for it)?
Isn't being the next successive sister group close enough for you? ;-) No
one ever said Nedcolbertia was the sister taxon of Ornitholestes. In fact,
the authors of Nedcolbertia's description conclude it is a coelurosaur
excluded from the Arctometatarsalia, Oviraptoridae and Dromaeosauridae,
probably close to Compsognathus and Ornitholestes based on pedal structure.
Nedcolbertia differs from Ornitholestes in several features-
- sacral centrum not dorsoventrally compressed
- distal end of pubic peduncle probably oriented horizontally
- obturator notch in pubis
- pubic shaft straight in lateral view
- ischial foot present
- distal end of femur more quadrangular
- more elongate tibia
- metatarsal II more expanded proximally in anterior view
*- metatarsal II longer compared to III
- pedal ungual II not enlarged
*- no intermetatarsal space between II and III
- metatarsal III less reduced anteriorly in proximal view
- metatarsal IV less slender
- pedal unguals more angulate in section
- pedal unguals with pits instead of flexor tubercles
Comparisons are hindered by the subadult and juvenile status of Nedcolbertia
material (not that we know Ornithoestes is adult), the fragmentary material
known for Nedcolbertia and the poor descriptions available of Ornitholestes.
The asterisked characters are from the pedal reconstruction of Nedcolbertia
that seems to be a cast, so I am uncertain whether all of the material is
actually preserved. Note that in most ways in which the two differ,
Nedcolbertia is more primitive.
Tyrannosauroids have always been outside Maniraptoriformes in my analyses,
as they are in Makovicky (1995), Forster et al. (1998), Sues and Makovicky
(1998) and Tom's most recent analysis (from May anyway). In Makovicky 1995,
Coelurus was below tyrannosaurids, although Ornitholestes was a
maniraptoran. Forster et al. 1998 had tyrannosaurids below Compsognathus.
Sues and Makovicky 1998 had tyrannosaurids below Coelurus and Ornitholestes.
Holtz had at least Coelurus and Scipionyx above tyrannosauroids.
Although Tom had Compsognathus below Ornitholestes in 1994, his most
recent(?) analysis has compsognathids above Ornitholestes. As I said, the
topology of this part of my tree varies insanely, but sometimes (like now)
Ornitholestes is below compsognathids. This might change in the future once
I separate Compsognathus and Sinosauropteryx, and add compsognathid
synapomorphies. The Santana compsognathid(?) places right below
Compsognathidae in my most recent tree, by the way.
You shouldn't be glad about Scipionyx's "position", as it is FAR from
certain. I can't emphasize that enough. It is somewhere near Coelurus and
compsognathids, but exactly where, I'm not sure. Any synapomorphies shared
by them PAUP would find in my most recent analysis would probably be
horribly supported in any case. Let's find out......
Oh look at that, two synapomorphies.
- ulnar shaft bowed
- semilunate carpal
Both forelimb characters that I've recently recoded while examining Holtz's
2000 matrix. Let's put the recoded version through PAUP and see what comes
Ah, a complete polytomy of tyrannosauroids, "basal coelurosaurs" and the
(Bagaraatan, Protarchaeopteryx, Segnosauria, Oviraptorosauria, Paraves)
clade. Told you not to trust the topology here. Picking a few random trees
shows the same topology as above, but without the Coelurus+Scipionyx clade.
Instead, Coelurus is more derived than Scipionyx. The good news is
Eotyrannus is finally grouping with tyrannosauroids.