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Coelophysis and Classification
Mickey Mortimer wrote:
Now, now Tim. You're not being quite fair there.
I know, I know. I'm just a diehard cynic.
We ALSO have one
species with good evidence of sexual dimorphism (though which sex
corresponds to which morph is unknown).
The idea of sexual dimorphism for the Ghost Ranch _Coelophysis bauri_ has
been disputed. I'll try and rustle up the references. Might be an SVP
abstract on it.
I spent a bit of time looking over the block at the RTMP to
code coelophysoids, there are definitely many robust individuals in
there and one gracile. I'm beginning to suspect the graciles may
actually be female.
I had a chance to talk with Alex Downs who works on these
guys at Ghost Ranch. He suggested to me that the "nasal fenestra" is
actually an error made when reconstructing the skull of rhodesiensis
from disarticulated elements. I think he's right here, the notch that
Raath interprets as a foramen actually seems to receive the lacrimal,
and you can see a similar construction in the structure of the nasals
of Ceratosaurus. Check out his paper in "Dinosaurs of New Mexico. New
Mexico Science Museum of Natural History and Science Bulletin No.17,
pp. 33-37" which talks about this and other aspects of _Coelophysis_.
Downs also notes that in almost every instance, Raath's illustrations
accurately depict Coelophysis bauri, the differences seem to relate
largely to proportion. Lamentably Raath's thesis has never been fully
published and remains very hard to get ahold of.
Anyways, regarding classification- it's totally arbitrary.
Classification is set up by definition, which means it's possible to
arrive at universal, proven truths in classification... but only if
you accept the starting principles. Which set of starting principles
we adopt is arbitrary.
We can arrange our paleontology library any way we choose.
Alphabetically, by taxon, by author, using the Dewey Decimal system,
the Library of Congress system, how much the books weigh (big stuff
on the lower shelves), by value (old Marsh volumes where they can't
get damaged), by subject material (biomechanics, sedimentary geology,
geochem, cladistics, ecology) even, heaven forbid, by aesthetics
(this is such a pretty book I'll put it at eye level), or a
combination of all these... no system or criterion is more correct
than the other, it's entirely a matter of what you want. Utility,
priority, aesthetics? Opinion, in other words. Classifying organisms
is no different; it's possible to be right or wrong in one's
classification of an animal according to this or that set of starting
principles, but which set of starting principles (monophyly,
aesthetics, priority) one chooses and how you employ them are totally
up to you.
One can argue for the Linnean system if tradition is what you
want, or the Phylogenetic Taxonomy which is big in dinosaur paleo
these days, if you think that monophyly and a system which can talk
easily about relationships is good. Or one could organize animals
into size-based classes, with shrews, earwigs and hummingbirds in
"Microtheria", while burrowing owls, pigs, and radiated tortoises go
in "Mesotheria" and elephants, giant squid and Diplodocus into
"Megalotheria", using the criterion of maximum adult body mass. If
you're into relationships, this wouldn't be terribly useful, but it
might actually be of particular interest to an ecologist comparing
body size in continents, islands, etc. The invertebrate paleontology
people look at survival of families across time, while freely
admitting that families are rather arbitrary and may be paraphyletic,
but to the extent that the family is an indicator of morphological or
ecological diversity (most of the things in a family would probably
tend to look alike and therefore tend to live alive) this is useful
and can say things about the evolution of life on earth.
It's a bit hypocritical of me to say so (okay, okay, a lot
hypocritical) but getting involved in heated discussions about
classification can be a bit, well, silly and unproductive. At the
core of it, it's no more scientific than a heated discussion about
the merits of the Dewey Decimal system versus the Library of Congress
system. ("Damn you Dewey Decimal nazis! When are you going to release
our library's volumes from your tyranny and see the light of the
Library of Congress system??").
Better check that name, Nick. I have a feeling that the name
"_Littlesquishythingyonthebottomofmyshoeus_" may be preoccupied by a genus
of Madagascan cockroach.
Oh please, do your homework. That would be "Bigasshissythingy..."