[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
(Hopefully not much more) cladobabble
Johnathon Wagner just addressed many of the points I was about to make, so I
can shorten this message. A few quick (?!) comments:
"Real" things: Just because something cannot be picked up or pointed at
doesn't mean it isn't real. I can't pick up a 1980 eruption of Mt. St.
Helens, nor point to a Taconic Orogeny, but I do not deny the reality of
these things. One could debate how precisely to define the beginning or the
end of either of these things, but that doesn't make them any less real or
less external to human reality (unless one persues solipsism, but then one
has to pretty much abandon science as a whole).
With regards to Jeffrey Mertz, I would agree that paraphyletic taxa are no
less "real" than monophyletic ones, but that the choice of monophyly as a
taxon criterion comes from other properties.
Character suite-based taxa: As mentioned earlier, defining taxa on whole
suites of characters results in some major problems. Specifically, in
dinosaurs, using the suite of characters I gave makes a lot of problems for
_Herrerasaurus_, in that it lacks three fully sacralized vertebrae. If it
is indeed a basal theropod, or even a basal saurischian, and if three
sacralized vertebrae are independantly derived for ornithischian and
sauropodomorphs + theropods, then what of Dinosauria? We are stuck with a
quandry: is "Dinosauria" di- or triphyletic? Do we label "Dinosauria" only
the FIRST branch to develop three fully sacralized vertebrae, and leave the
other one/two outside of Dinosauria?
Aptness of particular names and definitions: I agree that this is where most
of the concern comes in. Personally, I am much more comfortable with the
definition of Dinosauria that I and Olshevsky independantly derived.
However, I recognize that some means needs to be taken to determine which
name among synonyms will be chosen, and the preference is currently
priority. This does yeild some (indeed annoying) conditions such as having
birds as dinosaurs by default (rather than by discovery); by excluding some
classic "tetrapods" from Tetrapoda; etc. However, aptness of names or
definitions has never been a criterion in biological taxonomy:
_Psittacosaurus_ and _Protoceratops_ belong in Ceratopsia, even if they
don't have horns; _Dimetrodon_ has three types of teeth, not two;
_Basilosaurus_ is a whale, not a lizard, etc. As Wagner points out, at
least PT provides ONE explicit element in taxonomy beyond the type specimen.
(Incidentally, I use the _Ig_-_Meg_ definition for Dinosauria in my 100
level class, at least until after we're past the origin of birds.)
Playing in Peoria: Sorry, this one REALLY doesn't fly. As Jeff Poling
demonstrated on his webpage, the idea that "dinosaurs" and birds are clearly
distinct isn't supported. Sure, nobody can confuse a _Triceratops_ and a
hummingbird, but the morphological distance between a small dromaeosaurid
and _Archaeopteryx_ is VERY tiny. As bird origins become better known, the
supposed great morphological gap between birds and non-birds is very, very
hard to find.
If we teach only what the public wants to hear, then we aren't really
teaching. Say the general public doesn't want to hear that any group of
animal is the descendant of any other group of animal, or that the contients
have never moved. Should we arrange our classes so that we conform to these
beliefs, or should we show why (at least some) scientists accept these
events, how those data were obtained, and what methodologies were used.
The bewildering number of names: Sorry. Geez, I guess we all better stop
coming up with new names. While I'm at it, I better call up the
hydrologists and tell them to stop developing any new descriptive
terminology or methodology for aquifer systems. Hey, structural geologists,
stop finding new ways to classify and understand faults and folds! And no
new terranes, please!
Okay, the above seems silly, but that is essentially being argued here. It
may well be that some of the terms we are using are not helpful to you. I
can deal with that. They are, however, useful to me. I have interest in
mammal phylogeny, too, but I don't go on the vert paleo discussion group or
mammalogy groups and tell people: "I can't keep all these group names
straight, and I'll never use them anyway. Don't name any new names, and
don't define any names already out there."
It IS great that so many people are interested in dinosaur paleontology.
(It actually would be great to see the rest of paleontology get the same
kind of attention). But it IS a science, and it DOES have its technical
aspects, and sometimes those techincal aspects are not geared toward a lay-
or causual-audience. If somebody finds this distressing, I am sorry.
However, I wonder why they think that this particular field of study should
be less rigorous or less technical than any other aspect of historical
geology or evolutionary biology. (I do wonder if planetary astronomers find
the same kind of attitude?).
Thomas R. Holtz, Jr.
Vertebrate Paleontologist Webpage: http://www.geol.umd.edu
Dept. of Geology Email:email@example.com
University of Maryland Phone:301-405-4084
College Park, MD 20742 Fax: 301-314-9661