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> 'definition' is simply a convenient standard of delineating the taxonomic
> boundaries of the group with reference to a recent, commonly accepted
> phylogenetic theory. However, if the pertinent conclusions of that
> particular phylogenetic theory change significantly, then the group will
> redefined. This fulfills the interests of common sense and taxonomic
> stability. My impression of the phylogenetic systematics of dinosaurs is
> that this is happening all the time.
> Don't agree? Ask yourself whether, in the case of _Archeopteryx_ being
> found to be an outgroup to the Saurischia, you'd accept Aves > Saurischia.
> If you would, you deserve credit for being consistent in your approach,
> I would suggest that you've got the cart well and truly in front of the
Couldn't have said it better! One thing people tend to forget, it seems to
me, is that clade names are completely artificial constructs anyway, which are
just created to help scientists (and the general public) to communicate with
each other. Think about it: the animal we call Archaeopteryx probably
couldn't care less whether it is placed in a clade called "Aves", "Avialae", or
"Hiccups". Thus, the names are, above all, a means for us to communicate, and
within this framework, we should try to decide what is most useful form to
apply them. As pointed out by Nixon & Carpenter (2000) and Benton (2000), for
example, phylogenetic taxonomy (in its extreme form) tends to go for
epistymological correctness, but fails in terms of utility. Don't get me wrong:
nothing against applying phylogenetic definitions, node, stem, or
apomorphy-based, to certain clades, but this does ONLY make sense within the
the cladogram I am talking about (or others that, concerning this clade,
come to similar conclusions). If we use the same definition regardless of what
the cladogram looks like, we loose one of the most important aspects of names:
their use to communicate our concepts to each other. OK, I still know, for
example, that "Dinosauria" is the clade that includes Triceratops and
Neornithes and all decendants of their most recent common ancestor, but that
tell me anything about the contents of this clade, or how to recognize its
members, if I don't have the cladogram the user of the name is talking about.
If Galton was right that birds are the sister group to Ornithischians,
Dinosauria does not include Saurischia. If Welman was right that birds are
descendents from Euparkeriids, then Dinosauria includes all of Archosauriformes.
Wouldn't it be much better for understanding each other if, in extreme cases, we
could just adjust the name by proposing a different definition, cladistic if
you like. Thus, in the (admittedly extremely unlikely) case that Welman was
right, shouldn't we just say: Oh yeah, so the definition of dinosaurs we have
doesn't help us here, lets say for this hypothesis that Dinosauria is defined
as Megalosaurus and Iguanodon and all descendants of their most recent common
Another aspect of this dilemma is our communication with the general public,
and this is a very serious matter! Non-Biologists conceptualize animals by
their "looks" and if we are now every five years trying to tell them that what
they should regard as birds suddenly includes crocodiles, or does not
include chicken (if, on the basis of a definition of birds on the basis of
palaeognaths and Passer, Galloanseres are found outside this clade in an
they will certainly not be able (and not be willing) to follow these ideas.
HOWEVER, THIS IS THE GREAT MAJORITY OF PEOPLE WHO PAY FOR OUR RESEARCH!! If we
loose touch with them, we might face problems to continue our work. I know
that this is no argument for the philosophically correct taxonomists, but it is
an argument for those working in the field and trying to get their research
funded! Remember that names are a means to communicate, nothing more!!
Dr. Oliver Rauhut
Institut für Paläontologie
Museum für Naturkunde der Humboldt-Universität
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