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Re: Megalosaurus and Titanosaurus



George Olshevsky (Dinogeorge@aol.com) wrote:

<Clearly what we need here is to find, first, a theropod skeleton that has
the first kind of postcrania associated with a dentary, and second,
another  theropod skeleton that has the second kind of postcrania
associated with a  dentary. Then, if and only if >both< dentaries resemble
the type dentary of  Meg bucklandii will Meg bucklandii be a nomen dubium.
 
Just because we don't know which, if either, postcrania go with the type
dentary doesn't make Meg bucklandii a nomen dubium.>

  I am confident that at least half of the Stonesfield specimen belong to
the same animal that produced the type dentary. I just can't _prove_ this,
and therein lies the rub: neither can anyone else, so far. What we need is
a skeleton with the same kind of jaw. Even all the dentaries referred to
and including the paratypes for *Marshosaurus* do not resemble the type
jaw, but have gross features associated with it. The jaw then becomes more
diagnostic as the information spreads. Not so with *Megalosaurus
bucklandii* -- yet. Furthermore, the language of the authors is in the
mein of describing how it is impossible to prove yet which postcranial
remains belong to the type dentary, and based soley on the dentary and
deriving a diagnosis, it has been the general conclusion of various
authors that it is undiagnostic. Rescuers of the name have continued to
use the postcrania to support it, but how is it possible to use postcrania
you cannot determine to belong to the same individual or taxon in order to
diagnose the animal? The lectotype dentary _must_ be the key to
determining, so far, whether it is diagnostic or not, and that is how it
was indicated as a nomen dubium. This does not mean that further work
might allow others to suggest it is valid, but that these authors, now,
provide some data to show it is not diagnostic. Canning et al are working
on separating the taxa from each other in the Stonesfield Quarry, so it
will be some time before we have any idea what further can be determined.
Likely, the maxilla belongs to the same animal, but there were two large
tetanurines in the area, so that, too, is not something we have to work
with.

  And, just because one person determines a nomen dubium does not mean
others must follow suit. One can choose not to follow the conclusions of
the author, despite having the same data or more or less, but clearly
stating reasons is a good idea, and permits people to know where you are
standing. As in law, you make your prima fascia case, and its up to others
to follow or not. Paleontology has a lot of things in it, including
systematics, that depends soley on agreement. One man, say Ollie Rauhut,
can call many taxa nomina dubia, or metataxa, and non-diagnostic, but
others may hold different views or have different data, ideas, etc..

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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