Re: Strange thoughts on PN - was Re: BAD vs. BADD

[dinoboygraphics@aol.com]

Martin Baeker wrote: "Everybody here agrees that group 
A=(Megalos.+Iguanodon) is useful, as is B=(Passer+Archaeopteryx) - 
where () denotes MRCA - despite the fact that these are also quite 
arbitrary - there will be a critter looking *almost* like the first 
member of A that is not a member of it (like Lagosuchus), but still, 
the concepts are useful, albeit arbitrary.

Why is then A\B (A without-B) such a big no-no? From the frequency we 
hear "non-avian dinosaur", this gouping is *useful* for many purposes, 
except, of course, when discussing phylogeny, so, what is *useful* may 
get a name, at least a vernacular name."


In my opinion ths would be a disaster, not just for science education, 
but for science research.  Allowing yourself to slip into the "Group B 
took a "significantly different evolutionary direction" from group A" 
mode of thinking (as Jason did explicitly when he said "This is 
confusing and disconcerting because it assumes no real change occured 
between the groups...") is what hindered us so long in understanding 
dinosaur biology.  Because people (including scientists) "knew" that 
dinosaurs were reptiles, while sparrows and Archaeopteryx were "birds", 
we took over a century to start to form a consensus on the avian-style 
respiratory system that saurischians use.  Many are still having a hard 
time grasping that some non-avian theropods had not just dino-fuzz, but 
actual wings.  It prevented (most) researchers from seriously 
considering that non-avian dinosaurs had an elevated metabolism.

Giving arbitrary non-monophyletic groups names is heuristically 
damaging for the same reason that using Linnean ranks is a 
heuristically poor practice; naming them encourages people to think 
that the name or ranking is "real" in some ontologically valid sense.  
It may be "unwelcome" to some (maybe even most) people to have to use 
terms like "non-avian dinosaurs" or "non-human primate", but using them 
encourages us to be intellectually honest, by reminding ourselves that 
the group is arbitrary, and that we must be careful to ensure that the 
characters under discussion are actually restricted to the group at 
hand, not simply an illusory lumping of characters from animals we 
asssume are "alike" in some way.

By the way, I *always* refer to snakes as lizards.  They are, after 
all.  The interesting question is" Are they near igaunians, as some 
olecular studies have suggested, or are they closer to (or even 
withing) varanoids, as most other studies have found?  I suspect the 
latter, but time and more data will hopefully clear this up.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

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