Ostrom Symposium - Part I

[Ronald Orenstein <ornstn@home.com>]

Well, I'm back from the Ostrom symposium and although I suspect that Tom
Holtz will post a much more accurate and detailed report than I can hope to
do, I think it only fair to give members of the list who weren't there some
feeling of what went on and, if you can stand it, what I thought about it.
First of all, I must say that one of the nicest things about being there
was being able to meet a number of fellow posters to the list, including,
of course, Tom Holtz, and Mary Kirkaldy, who I hope by now is safely back
in Atlanta.  Hello again to everyone I met, and to a few of you who were
there that I wasn't able to catch up with, I hope there will be other
opportunities.

This is Part I.

The opening night on Friday featured the gala at the Yale Peabody Museum,
with people running around in Chinese costumes, performers on the shang,
lots of hors d'oeuvres, and of course, the fossils.  It was wonderful able
to see at first hand the famous specimens of Caudipteryx, Sinosauropteryx,
Protarchaeopteryx, and Confuciusornis.  There were six fossils in display
at all, including two Caudipteryx, the original Sinosauropteryx specimen
and the larger one containing a mammalian jawbone (which a number of people
who know much more about these things than I do suggested might actually
be a different animal), the only Protarchaeopteryx in existence, and a slab
containing two Confuciusornis, neither of which, unfortunately, had the
spectacular long tail streamers that show up  in quite a few of the
specimens -- about 20 percent according to Larry Martin, although Phil
Currie told me that a number of unexamined specimens bring the portion with
streamers up to about 50 percent.  Also on display were the two National
Geographic Society models of Caudipteryx and Sinosauropteryx.  It's a small
exhibit, but  when do you ever get a chance to see one so remarkable?  For
a non-palaeontologist like me, of course, there were the confusing
experiences of having Larry Martin explain to me in considerable detail why
Caudipteryx couldn't possibly be a dinosaur, followed by a number of other
people pointing out to me in equal detail why it not only had to be a
dinosaur, but an oviraptorisaur at that.  I suppose that I am more
convinced by  the oviraptor argument, but it certainly is interesting to
hear both sides.

Anyway, on to the symposium itself.  After an opening speech by John
Ostrom, the festivities began with a talk by Jacques Gauthier entitled
"What is a bird?".  This was a semantic discussion of whether we should be
calling just the modern crown clade of birds "birds", and everything else
by another name, or whether we should follow the pattern of almost any
ornithologist who's thought about the matter and consider everything from
Archaeopteryx on up to be a bird.  My own feeling, of course, it is we
should call anything a bird that looks like one, but since nobody can
decide what a bird looks like anymore, I suppose this is not going to be a
great deal of help.  On a more precise level, Gauthier was agonizing over
whether the definition of bird should be based on a descendant  tree or on
a shared character, and he left it for the rest of us to make up our own minds.

He was  followed by Hans Dieter Sues, who had the rather peculiar task of
describing alternatives to a theropod ancestry for birds -- peculiar, of
course, because Sues favours the theropod ancestry theory.  He did so by
running through a series of proposed alternatives and explaining why he
didn't think they fit the bill.  These ran from the megalancosaurids,
represented in the slides by Proterosaurus, which he dismissed as having no
features whatever resembling Aves.  He also pointed out that the  fossil
had seeds and ovules in its gut indicating that it was a plant eater, a
perhaps unlikely scenario for a bird ancestor.  He moved on to Longisquama,
which he also dismissed.  He pointed out that there was no clear evidence
in Longisquama of an anterorbital fenestra, which is certainly a featured
you would expect in a potential bird ancestor, and pointed out also that
the evidence showed that the plumes along the back, or whatever they are,
were most likely in a single row down the midline instead of the paired
structures that have been suggested by some.  He does not regard them as
proto-feathers.  He then moved on to Walker's theory of a pseudosuchian
ancestry, concluding that the similarities that have been pointed out
either fail when you start looking at them in detail, or represent
characters that are widespread in archosaurs and so are not too much use in
determining a bird ancestor.  Not surprisingly, his final conclusion is
that there is no evidence for a viable competitive hypothesis to
theropod-bird ancestry.

Sues also referred briefly to Scleromochlus, but could only conclude that
we need better material before any kind of clear interpretation of this
specimen can be made.

Paul Sereno, speaking on coelurosaurs and bird origins, announced what may
for some  be the biggest surprise to come out of the symposium -- the
latest on relationships of the alvarezsaurids.  For those of you who have
always wondered how Mononykus could possibly be a bird, I have good news
-- it isn't one.  Instead, the alvarezsaurids appear to be closest to the
ornithomimids.  They share a number of characters unique to that group,
including characters in the skull and in the first digit of the hand.
Ornithomimids  apparently are the only theropods that are unable to extend
the first digit of the hand, and this feature also shows up in, I suppose,
those alvarezsaurids that have more than one digit  -- at least if I
understood Sereno correctly (I'm a bit confused on this point).  Also, the
coracoid-sternal articulation of alvarezsaurids is unlike maniraptoriformes.

Sereno reminded us that we now have 10 to 15 times as much information
available on the question of bird origins as Jacques Gauthier had back in
1986.  This includes 27 consistent, stable characters supporting a modern
view of bird origins.   Sereno does not agree with Tom Holtz's
Arctometatarsalia, arguing that the arctometatarsal condition is actually a
homoplasy found in a number of forms.  He also  agreed that Caudipteryx
falls out as a sister group to the other oviraptors, which, of course,
implies that remiges and rectrices must have arisen quite far down the
tree, and are basal to maniraptorids.  

He also argued that Iberomesornis was a juvenile enantiornithine.

Next up was Tom Holtz, talking on, of course, Arctometatarsalia.   My notes
indicate that Tom now seems himself a little less certain that this is a
natural group, but I think I had better leave it for his report to go into
details on that one.   He noted that the semilunate carpal is basal to
Carnosauria and possibly lower down.  He reminded us that there may be a
gap of as much as 75 million years between the divergence of the various
maniraptorian groups and the first good skeletons that we have available,
something that, of course,  gums up the analysis a bit.   Tom suggested
that dromaeosaurs, therizinosaurs, and oviraptors  all had complex
feathers, although no integumentary material is known for any of these --
yet.  I say yet because of the rumors that I am sure a good many of you
have heard of further treats awaiting us from the Chinese sites, but since
everyone else was keeping hush hush about these things I suppose I should
too.  Besides, nobody would tell me all the goodies.  I'm as impatient as
the rest of you.

If the new Chinese therizinosaurid  is really a member of that group, Tom
believes that the maniraptorian radiation must have begun as far back as
the early Jurassic, or even the upper Triassic.

After lunch, Mark Norell continued what I can only describe as the march of
the cladograms.  I have no intention of getting into the continuous
argument about cladistics that rages on this list, but I must point out
that one of the key features of cladistics appears to be the generation of
slides that are completely illegible without the eye of an eagle or the
assistance of an extremely powerful telescope.  No matter.  Norell
concentrated on the Maniraptoriformes, and his chief conclusion of
interest, at least as far as I was concerned, was that he also finds
Caudipteryx to be a sister group to the oviraptors.  He made two
observations with which I can certainly agree: one being that there is a
lot of missing data out there and that that creates a problem, and the
other that he dislikes characters based on ratios of elements.

That ought to be enough for one message.  Stay tuned; when I start this up
again will be turning to Larry Martin's paper.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com