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TRUTH AND "TRUTH"
Chris Brochu wrote:
<<1. We stopped worrying about Linnean ranks because they have no
biological reality and can seriously mislead people. They were made for a
world view that did not account for evolution. Good riddance to them.>>
and Tom Holtz (looking forward to the Gaia paper) also wrote:
<<We could take the typological approach and say "aha, this specimen does
not fit the features required to be a carnosaur, so it has to be in some
other category". Or we can take an evolutionary approach, sort out the
distribution to the best of our current ability, and see what results (in
this case, that tridactyly evolves independantly in derived carnosaurs and
If your goal is recovering the history of life, then I recommend using a
repeatable scientific methodology. If your goal is nice, neat lists of
names, then typology is fine.>>
I think that here we have the best summations of why we should abandon all
old, Linnean classifications and go with a completely evolutionary and
scientific system. Linnean classifications and ranks are best suited for
the times when evolution wasn't really thought of (except by David Hume in
the 1750's, and published in 1776, but that's a different story). Linnean
ranks are the expression that all things living and non-living have some
sort of cosmic rank overseen by the hand of the Almighty. They are also an
extention of the ideas of Aristotle who thought that all things on the tree
of life are subservant to man. In reality, there are no real "ranks" in the
tree of life, everything is equal.
Scientifically, cladistics is on higher ground than any system founded in an
idea of cosmic ranking. We can appreciate how Linnean classifications
taught us more about life than systems that came before, but this is the
same situation as astronomy coming from the pseudoscience of astrology.
Sure astrology gave us the basics of our science of astronomy, but that does
not mean that we shall hold on the astrological principles that the planets
relate in some way to our futures and destinies (assuming there is a such
thing as a "destiny").
Linnean classifications are inherently pseudoscientific; they ignore the
random nature of life, give subjective ranks to subjective groups, and they
are really easy to turn into anti-evolutionary charts.
All of this aside, let me turn to some more Tom Holtz arcana :-):
<<In support of theropod systematics, it is *VASTLY* more stable than (say)
Just to play devil's advocate for a bit (every cause needs one!), is
theropod systematics *really* more stable than eutherian systematics or is
this just an illusion we have based on a lack of specimens and data? Lets
face it, fossils come from select areas, and we are most likely getting only
sampling of true theropod diversity and only a smidgeon of anatomical
knowledge (soft tissues are just as important as bones you know). If we had
just the skeletons of a select few eutherians, say _Canis_, _Pan_, Homo_,
and _Physter_ our tree would look fairly simple. _Pan_ and _Homo_ would
group together strongly and you would have some debates over _Canis_ and
_Physter_ but you would probably say that _Canis_ is more closely related to
the _Pan_+_Homo_ clade. Add more layers of skeletal specimens, the picture
will muddy a bit. Where do rodents fit in? Those pesky anteaters don't
know where to go. Are whales ungulates? Hyraxes and elephants have similar
teeth, but then are elephants related to rodents? Where do bats fit in?
The whole picture gets muddied substantially with more data and specimens
coming in. Each new specimen overturns some relationships and adds more
texture. Your original tree seems correct in broad perspective, but things
proceed less in a easy pattern. Now we introduce into our world living
specimens, with soft anatomy. Systematists go bananas. Now we deal with
the eutherian reproductive system, cranial sinuses, intercranial veins and
arteries, eyes (!), ears, noses, and hair, all that hair! Everything
becomes a possible character. Everything is confusing. Then somebody
starts to work on molecules...
Now, scientifically we can't (and shouldn't) speculate beyond the evidence,
but phylogenetic trees based just on osteology and/or fossils are limited
because you can only infer stuff on soft tissues, which make up most of the
bodies of living things. We only have a general idea about most soft
anatomy. You have no idea about molecules. Looking at something with such
limited knowledge is easy because you don't have to think about the
complexities of soft tissues and molecules.
Now, of course, you can argue that since evolution is random in the
directions that it takes, and you cannot apply many strict rules as to how
it will turn out, you can say that the theropod tree is really easier to
untangle and more resolved than the eutherian tree. This is not the point I
am trying to make. The point that I am trying to make (among others) is
that phylogenies will always be changing because our knowledge will never be
complete. Each new find will cause changes in branching patterns in trees.
This is why cladistics works and Linnean systems don't. Phylogenetic
analyses have no real set hierarchy, definitions will always be changing
just like they are supposed to in science. (The origins of this idea go way
back. Back to Descartes and Locke.)
<<Where conflict does exist, it gives us specific research topics to
investigate: alvarezsaurids and troodontids and therizinosauroids come to
<<Contrast the above to the situation in Eutheria or in Neognathae, and
you'll see that we general theropod systematicists are in agreement over the
basic structure; it is the nitty gritty details that have to be sorted out,
and this means looking at the fine-level structure of anatomy and
Sometimes I wish some arch-angel will tell me the true tree for Neognathae;
the whole group is basically an unresolved polytomy. Sure, galliforms and
anseriforms probably are a seperate group from the rest of neognaths, but
then again anseriforms could be modified shorebirds, flamingos, or storks.
Galliforms could be more closely related to paleognaths. Passeriforms may
even be more basal than traditionally thought. Then again, if an arch-angel
tells me the "true tree", where's the fun of discovery?
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