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Re: BAD vs. BADD (was: Re: Most popular/common dinosaur misconceptions)

On 8/19/06, Jura <pristichampsus@yahoo.com> wrote:

I'm afraid I don't quite get what you are saying here.
Why is it okay to call a bird a dinosaur, but it's not
okay to call a snake a lizard?


"Lizard" is a purely vernacular term, while "dinosaur" is a vernacular
form of a formal taxon (_Dinosauria_). Snakes are squamates, but not
lizards. "Lizard", like any vernacular term, is governed by popular
usage.

Just because the initial change from theropod to
_Archaeopteryx_ was small, doesn't mean that labeling
that spot as a nomenclatural splitting point, isn't
useful.


Why must it be labelled as a "splitting" point, and not just as a
point? Why not place a "splitting" point at _Eumaniraptora_, or
_Maniraptora_, or _Orniththoraces_, or _Therizinosauria_, or
_Ceratopsia_?

There is no objective criterion for distinguishing a "splitting" point
from any other point, so let them all just be points. Then we can
recognize as many as are needed, without dithering over where to "cut"
something that isn't discontinuous.

From Archie (presumably), birds went off in a
completely different direction from dinosaurs, and
became wildly successful at it.


By this you are saying that all non-avian dinosaurs were evolving in
the same direction. The fact is that *every* lineage evolves in its
own direction; ceratopsids and tyrannosauroids and titanosaurs and
ankylosaurs and dryosaurids are all hugely different from each other.

(And if you point out that those are all terrestrial, then you have to
acknowledge Classes Chiroptera, Cetacea, Sirenia, Pinnipedia....)

This is like how
snakes went in a separate direction from lizards, and
became highly successful at it.


It seems to me that many lizard lineages did go in a similar
direction: glass lizards, worm lizards, etc. Snakes happen to have
been the best at it (so far), but why would that separate them from
other squamates?

Did you mean "can't change?" Then I'd say yes, if the
incorporation only leads to confusion and the erection
of new terms to denote what the old ones mean. So I'd
say no to "non-avian dinosaur" just like I'd say no to
"non-eukaryotic prokaryote."


"Prokaryota" is not a clade--"non-eukaryote biote" is probably what
you want, but there's already a handy informal phrase or three for
that group ("prokaryote", "bacterium", "moneran"). There isn't one for
"non-avian dinosaur", once birds are included as dinosaurs.

I have argued before that "non-avian dinosaurs" aren't really that
interesting as a paraphyletic group, anyway, and the term is only
popular because of historical reasons. If you're talking about flight,
talk about "terrestrial dinosaurs" or "non-avialan dinosaurs". If
talking about feathers, just talk about "unfeathered dinosaurs". If
talking about the extinction, talk about "Mesozoic dinosaurs" and
perhaps "non-neornithean dinosaurs" (or "non-avian" if you use the
crown clade definition). Think about the context before you decide
that "non-avian dinosaur" is what you want, because 9 times out of 10
there's a more appropriate term.

Incidentally, we cal also talk about non-avian maniraptors, non-avian
theropods, non-avian archosaurs, non-avian diapsids ... it goes on and
on....

How is using a separate set of nomenclature for birds
and dinosaurs (as was traditionally done prior to the
1990s) worse? Why is a hypothetical cut-off point so
hard to accept?


Becuase the gap has been pretty much closed. There are numerous
specimens now that are not unambiguously on one side or the other. The
distinction has become an ordinary one, not a "splitting" one.

If anything, bats provide a far, far better case for splitting, since
there is so little in the way of transitional forms.

For instance, I do see a
problem with the term: "non-mammalian pelycosaur."


Me too, since "Pelycosauria" is not a clade, and all "pelycosaurs"
(non-therapsid synapsids) are not mammalian, anyway.

This makes no sense. The basics of so many aspects of
science are arbitrary in nature. Look at SI units such
as the meter. Prior to its ties to light, it was once
measured as the distance between two engraved lines on
a platinum-iridium bar. Before that, it was measured
as 1/10,000,000th the distance from the equator to the
North Pole. Talk about arbitrary. The second was no
better. Its current definition is defined as the time
it takes a Cesium atom to vibrate 9,192,631,770 times.
Both are completely arbitrary in nature, yet look at
all that man has accomplished thanks to these units.
The same can be said for the arbitrary way in which
atoms are represented on a piece of paper, or in
models. Their fundamental properties may be arbitrary,
but the proportional relationships garnered from them,
are not.

Same goes for the old Linnaean rank system. 

No. The length of a meter may be arbitrary, but, since it is the same
in all circumstances, it is useful as a frame of reference. The same
cannot be said of Linnaean ranks. _Struthioniformes_ and
_Ornithischia_ and _Coleoptera_ are not somehow equivalent to each
other simply because they have traditionally been cosidered orders.

A meter measures physical distance. All a Linnaean rank measures is
historical convention.
--
T. Michael Keesey
The Dinosauricon: http://dino.lm.com
Parry & Carney: http://parryandcarney.com