Re: Old Monographs/ New Papers

[Nick Longrich <nrlongri@midway.uchicago.edu>]

>Speaking of waiting for papers...
>
>Dr. Tom said a while back that _Coelurus_ was going to be *very* important to
>future theropod phylogenetic analyses (presumably because of some good new
>material).  Well, I've heard hardly a word about this little beastie since
>then.  What's up?

Actually, it already is; check out Makovicky and Sues 1998- excellent study
and the first since Gauthier to use Coelurus. Coelurus has *far more*
phylogenetic information preserved in the holotype than does Ornitholestes.
All the more reason it's really too bad that so little has come out on it
since the nineteenth century despite the fact that the bones are readily
available for study. I think the real reason it's left out is that it lacks
a skull and that people tend to spend a lot of time on the skull.
Admittedly it's fragmentary but what it does preserve is very telling. And
when it comes down to more taxa vs. more characters, you pretty much say
"time to plug in some more taxa"; taxa break up the long branches- "missing
links".
        The Coelurus type does not preserve a true semilunate carpal (I've
got an SVP abstract that discusses this). And the thing I saw on the
Coelurus at SVP struck me initially as looking like a radiale, not a
semilunate. But Coelurus *did have* a semilunate. The elements preserved
are simply the medial halves of the bones that would eventually fuse
together (as the animal matured) into the semilunate carpal.
        On the other hand, the femoral head is really primitive- the animal
is juvenile but it still has a big fourth trochanter (maniraptorans do not
actually lack fourth trochanters; they just grow them very late in life)
and lacks the trochanteric crest of dromaeosaurs,
oviraptorosaurs+caudipteryx, therizinosaurs, troodonts, alvarezsaurs, and
birds.
        The astragalus is very tall, typical maniraptoriform, very slender
fibula, very long tibia and metatarsus. The caudals have short
prezygapophyses, which is a maniraptoran feature- people just usually
forget to look past dromaeosaurs, which pretty obviously derived their long
prezygs from short ones. Ulna is the typical maniraptoran bowed
arrangement; the humerus is pretty much what you'd expect on something like
an oviraptorid or dromaeosaurid w/o the big internal tuberosity of a
deinonychosaur. The ankle suggests an Ornitholestes/Allosaurus like
configuration. Greg Paul has suggested this as an Ornitholestes-Allosaurus
feature, but I also see some pretty similar stuff in the ankle of
Afrovenator, and I see a way to derive the tyrannosaur ankle from this
configuration, so my suspicion is that it's the basal condition for
Afrovenator+Aves, with the condition being modified in tyrannosaurs, lost
in ornithomimids, and then lost again in maniraptorans more derived than
Coelurus.
        Note that all of this info doesn't come from the new specimen. It
*all* comes from the type. The type is wonderful, the type is beautiful,
the type is in Yale and there is no problem getting access to it although I
doubt they'd let you do a monograph on it. The main thing I remember from
the one they showed at SVP is a short, but very strongly backturned
coracoid like oviraptorids or, to a lesser degree, dromaeosaurs
(dromaeosaurs having an acute angle between scapula and coracoid).
Supposedly this specimen is bigger, ergo a new species... it seems a lot
more parsimonious to say it's just an adult, unless you can either show
that it's no more mature than the smaller type, or that there are some
non-ontogenetic differences between it and the type.
        Coelurus vertebrae(well, vertebra) are also found in
Cleveland-Lloyd, incidentally, along with Ornitholestes (pers. obs.). I
wonder exactly what lurks in there to be discovered. We may actually have
the ilium- the thought has crossed my mind and others as well that
Stokesosaurus' ilium is about the right size and shape for an adult
Coelurus (notice the downcurved posterior margin; the medial ridge is also
found in the Yixian ?maniraptoran GMV 2124). There is a manual claw which
is too big for Ornitholestes, and pretty clearly belongs to a maniraptoran,
it may come off of an adult Coelurus. Problem being that it doesn't really
help you much to find isolated chunks of Coelurus- if you can't say they
are coelurus.

-N