Re: Hanson 2006, Mortimer, Baeker response

[mike@miketaylor.org.uk (Mike Taylor)]

Michael Mortimer writes:
> In regard to the theme of this thread, finding 'new' categories of
> dinosaurs is impossible in a way.  At least in the sense of broad
> groups like Sauropoda.  After all, Dinosauria is defined to only
> include Saurischia and Ornithischia.  So any dinosaur has to fall
> into those clades.  Saurischia is defined to only include
> Sauropodomorpha and Theropoda, so again, any saurischian will be one
> of those.  A sauropodomorph is either going to be a prosauropod, a
> sauropod, or more basal (like Saturnalia, Thecodontosaurus, etc.).
> And similar statements could be made for any dinosaur group.  Our
> current knowledge and phylogenetic taxonomy give us a well-supported
> backbone, and all that's left is to fill in the gaps.  But that's
> how it is with any clade of organisms whose phylogeny is well known.
> And the gaps are sometimes huge.  So there's still plenty of work to
> do.

I now find I don't need to reply to Tim because Mickey said _exactly_
what I was going to say.  I think any disagreement between Tim and me
here is just cross-purposes.  Of course in saying that _Tendaguruia_
and _Agustinia_ don't "fit at all convincingly into any of the
established clades less inclusive than Neosauropoda" I wasn't
proposing that there must be other Neosauropod clades besides
Diplocodoidea and Macronaria :-)  Just they they are morphologically
so freaky that they're not "a good fit" anywhere.  So that if we
accept that the notion of "families" is a useful one (on which see
below), then it does indeed make sense to accept Bonaparte's erection
of Tendaguriidae and Agustiniidae.

> Tendaguria seems to have gotten its own family largely because
> Bonaparte was being more phyletic than cladistic.  The dorsals were
> different enough from Saltasaurus that he figured it deserved to be
> separated.

Yes indeed.  But I don't have a problem with that.  Just because we
(mostly) all agree that families are not objectively real, it doesn't
follow that they have no utility.  (Much the same argument applies
here as with genera: I guess most of us would fall on the side that
says genera are not real, but it doesn't stop us from discussing them
all the time.)

So to go back to my original point concerning _Tendaguruia_,
_Agustinia_ and the unnamed third example, rather than claiming that
they fall into clades that no-one knew existed, the thing that excites
me is how morphologically distinct they are from all the well-known
taxa that you see on all Upchurch's and Wilson's cladograms.  After
all, if you're prepared to write _Agustinia_ off as "just a
titanosaur", then you also have write _T. rex_ off as "just a
coelurosaur" :-)

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  "Object-oriented programming is an exceptionally bad idea which
         could only have originated in California" -- attributed to
         Edsger Dijkstra.