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On Names and topicality...



Before I get into the things that will amuse, delight and infuriate
you, let me remind everyone that Creationism does not belong on this
list, and your breathing privileges can be revoked for ignoring that
ban.  (I hope I didn't amuse, delight or infuriate anyone yet).

A little over a week ago, a question about dinosaur name pronunciation
was brought up.  For a different take on the subject than any brought
up in response, I recommend the last paragraph of:

http://www.cmnh.org/fun/dinosaur-archive/1994Nov/0069.html

The words were penned by Ralph Chapman, and I'll extract one sentence
here because I think the sentence is apropos not only of discussions
of pronunciation but also of word usage:

] The point is that the names are there so we can communicate and as
] long as I can figure out who you're talking about, and vice versa,
] we have succeeded.

Tom Holtz seems to be taking a lot of flack right now for defending
phylogenetic taxonomy, and I'd like to defend his stance by
reinforcing something he wrote in another context and thus which many
of you might at first think is irrelevant:

> this is not a "dinosaur chat line"; it is, as Mickey Rowe has to
> point out every so often, a list dedicated to dinosaur *science*.

I re-broadcast it here not because I like to see my name in lights
(though who doesn't :-), but rather because I want to make it clear
that Tom is coming from a particular perspective -- as a person who
creates taxonomic nomenclature (e.g. Arctometatarsalia) Tom is a part
of an academic conversation that most of you are merely observing.
Tom's conventions about the meanings of taxonomic names are (so far as
I can tell) within the mainstream of contemporary science.  As such,
if you really care about science (as something that scientists do)
then you should accept the spirit of Tom's usage *in the context in
which Tom is writing* (I hope you can now see the relevance of the
quote!)  In that context, dinosaurs are reptiles.  Finished.  End of
story.  If you don't like that (or anything else related to
phylogenetic taxonomy) then you should probably complain on a
different list -- either one that deals more generally with biological
nomenclature or one that exists for some reason other than to discuss
contemporary science.

Two of the people in my lab just completed a herpetology course that
they designed.  They did not discuss birds or other dinosaurs.
However, they did teach their students that they were discussing a
paraphyletic assemblage of animals (_sensu latu_ :-), and they did all
they could to make sure that the students understood that the reptilia
(as defined by contemporary biologists) encompasses birds.  (And they
did it without me harassing them about it... though I harassed them
anyways :-)

Bottom line; there may be a question about what it is you want a name
to tell you, but that "what it is" can and should be somewhat
context-dependent.  In the context of this list decisions on taxonomic
nomenclature are made by the people making taxonomic nomenclature (not
arm-chair quarterbacks).  That is, people like Tom.  Contrary to the
"baggage" argument, using older terms makes sense within this context
because Tom's conversation isn't just (or even primarily) with the
people of this list -- it's also with his intellectual ancestors and
descendents.  There is a continuity in the usage of the term reptilia,
much as there is (if we can take Larry "I love TV" Dunn's word for it
:-) continuity in the usage of the term freedom (or liberte, I guess).
(Now please nobody tell me that that's a Yang worship word and that I
shouldn't speak it :-)

Lastly, since there have been a couple of incursions into my bailiwick
I figured I should pick some nits.  Dr. Tom wrote:

> Mammals have only two (most groups) or three (primates) types of
> color receptors.  

If you really want to know about this subject, you should look at work
by Jerry Jacobs (see references below).  Anyhoo, Tom left out the
possibility of there being only one (which appears to be the case in
some procyonids if by "color receptors" Tom means cones -- Jacobs and
Deegan, 1992).  It's also possible that some of us (humans) have four
(although the spectral sensitivity of the fourth is roughly identical
to that of one of the others since we are possibly in the incipient
stages of a gene duplication event -- Neitz, Neitz and Jacobs, 1993).

And also it should be pointed out that Tom's basic fact might be wrong
here because we know virtually nothing about color vision in diurnal
marsupials.  There are many features found in reptile retinas that are
not found in Eutherian mammal retinas, one of them being the cone
complement that Tom keeps bringing up.  However, many of those
features lacking in Eutherians are retained in Metatherians, and it is
possible that cone complement is among them -- we just don't know yet
one way or the other (Jacobs, 1993 -- so far as I know, that gap has
not been filled during the last five years).

> Reptiles (including birds) have more.

Also only generally speaking (but to the point of Tom's discussion, it
is pretty well certain that the MRCA of extant reptiles had more).  

> They thus have the potential to divide up the color spectrum MUCH
> more finally than even we can.

Dr. "I make plenty of grammar mistakes myself" meant finely, I'm sure,
but it should be pointed out that this isn't necessarily the case even
after that correction.  The fourth cone in reptiles is frequently a UV
sensitive cone, so the animals aren't necessarily making finer
discriminations; they're making discriminations over a broader part of
the spectrum (Goldsmith, 1990).  That's just an obvious example where
it's clear that not just the number of receptors, but also their
spectral range is important for the conclusion Tom has drawn.  The
fineness of spectral discriminations varies with location along the
spectrum within individual animals because of this nuance (because of
our peculiar photoreceptor complement we're particularly good at
discriminating differences at wavelengths around 580 nm FWIW).

Finally (and I do mean finally!) I would take issue with Tom's usage
of the phrase "color spectrum".  It conflates a concept from
perception (color) with a concept from physics (spectrum).  For gosh
sakes let's keep these amateurs from throwing around terms that
scientists try to define carefully! :-)

References:

Goldsmith, T. H. (1990). "Optimization, Constraint, and History in the
     Evolution of Eyes", _Quart. Rev. of Biol._ 65(3):281-322.

Jacobs, G. H. (1993). "The Distribution and Nature of Color Vision
     Among Mammals", _Biol. Rev._, 68:413-471.

Jacobs, G. H., and Deegan, J. F. II (1992). "Cone photopigments in
     nocturnal and diurnal procyonids", _J. Comp. Pysiol. A_
     171(3):351-358.

Neitz, J., Neitz, M., and Jacobs, G. H. (1993).  "More than three
     different cone pigments among people with normal color vision",
     _Vis. Res._ 33(1):117-122.

--
Mickey Rowe     (mrowe@indiana.edu)