[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: news from dino central




-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
David Marjanovic
Sent: Saturday, June 16, 2001 2:36 AM
To: dinosaur@usc.edu
Subject: Re: news from dino central

* > Seems like my knowledge is lagging behind a bit or two -- I thought
> > *Nedcolbertia* was close to *Ornitholestes*?

Sure my knowledge is lagging behind -- I was relying on "Dinosaurs: The
Encyclopedia" which mentions the yet-unnamed *Nedcolbertia* after
*Ornitholestes*. :-]

> Nedcolbertia differs from Ornitholestes in several features-
> [...]
> - ischial foot present

This is quite basal indeed. Convinced me :-) But tyrannosaurs don't have an
ischial foot...

> [...] As I said, the
> topology of this part of my tree varies insanely, but sometimes (like now)
> Ornitholestes is below compsognathids.
> [...]
> Ah, a complete polytomy of tyrannosauroids, "basal coelurosaurs" and the
> (Bagaraatan, Protarchaeopteryx, Segnosauria, Oviraptorosauria, Paraves)
> clade.  Told you not to trust the topology here.

I see. So anyone can come and suggest another topology without suffocating
under mountains of evidence? :->

> 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

How did these come out as synapomorphies? I mean, lots of others have one or
both... *Ornitholestes*? Maniraptoriformes? ~:-|
How do you define the semilunate? Does *Allosaurus* have it, or does it have
to be bigger, like in e. g. *Ornitholestes* and dromaeosaurs?

> Eotyrannus is finally grouping with tyrannosauroids.

Why "finally"? Didn't it before? Is it _so_ basal, or just too fragmentary?
This is something that gets me about cladistics. You have to place the
animal in a genology. You have to find its 'cousin, sibling, etc.' but you
really really can't. With the Linnaean system, you can just say it's a
coelosaur and not worry about it. You don't have to make up new names for a
group to place it next to another animal. We don't have to listen to a dozen
people making a dozen cladagrams using, more or less points, where there is
no consensus on what to use, and we can have hundreds of cladagrams (I'd
like so see some papers where they are all listed) and not be any closer
than we were before. No offense Tom, but we don't have to hear a talk where
the speaker says, oh, don't go by these cladagrams, I've changed it.

And Eotyrannus can be just a tyrannosauroid and not worry about it.

Well, that's my 2 cents worth.

Tracy L. Ford
P. O. Box 1171
Poway Ca  92074
*