RE: Opisthocoelicaudia and cladistics (was Re: Titanosaurids) (long)

["Tracy L. Ford" <dino.hunter@home.com>]

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Williams, Tim
Sent: Wednesday, January 23, 2002 2:32 PM
To: 'dinosaur@usc.edu'
Subject: Opisthocoelicaudia and cladistics (was Re: Titanosaurids) (long)


George wrote:

<< Well, that's THREE characters (the first two of which may be
<< functionally  correlated) all of which can be readily interpreted as
<< autapomorphies of the genus _Opisthocoelicaudia_.

>No, that's >dozens< of characters, since there are lots of dorsals,
>caudals, and sacrals that are different.

Does that mean we have to count every individual feather of
_Archaeopterx_ to find out how many characters it shares with
modern birds?  Jeez Louise!<<

I love it when people get so fregin SARCASTIC!!! Let me try. Nawh, never
mind.
The point is not to just take a few individual points from just a few
vertebrae, but you have to look at the WHOLE animal! What, that MAY mean
having to actually look at the animal! Heaven forbid!

>The appendicular characters are minor and
>insignificant, and can easily come about through convergence, because
>all sauropods had to walk and carry great body mass.<<

This cuts both ways.  The bifid neural spines had a purpose too (yeah,
that's right - they weren't just there for decoration). <<

NO REALLY!!! (Ok, I'm being sarcastic).

>> The functions ascribed to bifurcation of the neural spine imply that this
character be
expressed serially down the column (or a section of it), so I don't think
it's valid to score each individual vertebra as an isolated character.<<

And the function is?

>The big problem with cladistics is that there is no way to weight
>characters, so it becomes a phony one-character-one-vote situation. You
>can't equate a character that appears everywhere along the spine with a
>character that is a single small lump on a long bone. Cladistic
analysis >is not necessarily a democracy.

Nor should phylogeny be ruled by characters we happen to like the most.
Then we're back to birds evolving from megalancosaurids, simply because "my
sixth sense tells me" that long arms and a triangular skull of
_Megalancosaurus_ carry more weight than the 135 characters that place Aves
within the Theropoda.

Certainly, this is an extreme example (and I'm not accusing George of
subscribing to such nonsense). <<

Kind of sounds like it though.

>> But it illustrates the point that we shouldn't pick and choose our
characters - unless we have damn good evidence
that they're developmentally or functionally linked.<<

But this happens all the TIME!


Rutger Jansma wrote:

>Because of it's stiff tail, Opisthocoelicaudia wasn't able to contact
>the ground, leaving the specially adapted chevrons useless. If
>something is useless in nature, look at the example of the monkey-tail,
>it gets reduced and eventually get lost.<<

You may well be right in this explanation.<<

But the tails were useful for something or else they'd have been lost a long
time ago. Some diplodocids have ossified tendons to the tails were also held
stiffly, but they have a real long tail.

>Diving dinosaurs are probably something we could only fantasize about
>untill some evidence has come to light.

Fantasize no more!  We already know about those sexy hesperornithiforms,
penguins, puffins, ducks, loons ... :-)<<

Oh, Jeeze, why do everyone always bring up birds, when the person is
actually talking about dinosaurs?


Tracy Ford wrote:

>To me, it's pretty ludicrous that there is only one group of Late
>Cretaceous Sauropods.

Morphologically speaking, the Titanosaurifomes is very diverse - especially
when it includes everything from _Brachiosaurus_ to _Pleurocoelus_ to
_Andesaurus_ to _Phuwiangosaurus_ to _Aeolosaurus_ to _"Titanosaurus"
colberti_" to _Saltasaurus_ to _Opisthocoelicaudia_ (yes, even him).  I
think the success of the Titanosauriformes in the Late Cretaceous is
analogous to the success enjoyed by the Maniraptoriformes at around the same
time - except that the dominance of titanosauriforms was global.  (Maybe it
was for maniraptoriforms as well!)<<

NO, no, no. This assumes that all sauropods ARE titanosaurs and they go from
there.
Nemgetosaurs are Diplodocids, Brachiosaurs are Brachosaurs,
Opisthocoelicauda is a Camarasaurid, and Titanosaurs are Titanosaurs.
Nature is very diverse and people need to understand that and not have
tunnel vision with cladagrams.

>The Diplodocid looking titanosaurs,are IMHO diplodocids, the Camarasaur
>looking titanosaurs are IMHO camarasaurds, etc. There is new evidence,
>still being worked on, that will...Ok, I won't be mean...

If new evidence backs that up, terrific!  The more the merrier, when it
comes to sauropod diversity.<<

Yea, and then we'll also see people arguing against this because THEIR
cladagram says otherwise. I've seen this happen way to many times. I do go
to symposia and read papers.


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