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What Is Not a Dinosaur? (was re: Ankle Articulation in Pterosaurs)

I read with interest Jonathan R. Wagner's response to the question I
posted re using ankle articulation to define one of the differences
between dinosaurs and pterosaurs. I think I follow the line of thought, but I
felt the need for comment and clarification.

On Mon, 20 Jan 1997, Jonathan R. Wagner wrote

>         Simple solution, DON'T EXPLAIN this way!  While I understand that
> layfolk do not have an easy time with science, we cannot afford to dummy
> down science to this level.  I had an argument on just this topic recently
> witha  geophysics professor, who was aggravated because "you paleo types"
> keep giving people new definitions of what a dinosaur is or isn't.  Using
> simple anatomical definitions for groups only encourages commoners to engage
> in trivial and useless semantic debates, and miss the point.  Give them the
> actual scientific reason.
>         Tell them this, "Through detailed analysis of the anatomy of
> pterosaurs and dinosaurs, some scientists have suggested that the two groups
> are closely related.  However, dinosaurs are the group of animals which
> decended from the common ancestor of ornithiscian and sauriscian [you may
> have to explain these to adults] dinosaurs, and pterosaurs seem to have
> branched off before this point.  Therefore, pterosaurs are not dinosaurs."
> For the sophisticated audience, you may of course point out that this is
> largely arbitrary, and if you go into cladistics a little, you can explain
> taxonomic priority, and then they will have their reason.  

        What prompted my questions in the first place was a statement made
by Currie and Koppelhus that "most of the traits that identify them
[dinosaurs] are found in the hind legs." In their answer to the question
"What is a dinosaur?" no specific reference is made to the hip structure
(although they DO state in their answer that along with the hind leg
traits "these and other skeletal features are used by scientists to define
the Dinosauria." The emphasis on the hind leg as a factor in defining
dinosaurs led me to the Wellnhofer book on pterosaurs, which also put some
focus on the hind leg articulation as a way of pointing out the difference
between the two groups.
        I am trying to explain to kids ranging from kindergarten through
grade 3 why pterosaurs are not dinosaurs, and I'm not sure that telling
them, "You'll understand it when you're grown up and learn about
anatomy and dinosaur systematics" will work. I do teach them to sort
dinosaur models (a combination of the Carnegie and the Boston Museum of
Science models) into lizard-hipped and bird-hipped. When we do this
exercise, I only provide them with dinosaurs. Maybe I should throw in a
Pteranodon so they can sort it out as "None of the above?"

        I was surprised by the opposition to using "simple anatomical
definitions" in defining the Dinosauria. I mean, sure, there's a
complicated, highly scientific way to explain the difference between an
insect and a spider, but there's something wonderfully economical in being
able to say, "One way to tell them apart is that insects have six legs and
spiders have eight." (I don't think this will confuse people who see an
        The statement "We can't afford to dummy down science to this
level..." struck me as unusually critical. Where is the line drawn between
"dummying-down" and "explaining in lay terms?" Are the coffee-table
dinosaur books by Lambert and Norman "dummying down?" Is it dummying down
to say that "Dimetrodon is not a dinosaur because its legs were oriented
in a sprawled stance rather than an upright one" or "Dimetrodon is not a
dinosaur because it lived in the Permian period." That will linger much
longer in a child's mind than a treatise on pelycosaurs.
        Our proximity to the Smithsonian Institution provides us with the
opportunity to show the kids what a mounted dinosaur skeleton looks like.
I can tell the kids, "Look at the way the Allosaurus is walking." They can
get a sense of what digitigrade means by seeing it even if I don't use the
        There are a lot of public school educators who lurk on this list
because they want to present information as accurate as possible about
dinosaurs to the children they teach. When I first arrived at my school,
the teachers were telling the kids that Pteranodon was a dinosaur. For the
past three years, the teachers have been making a genuine effort toward
improving the presentation of dinosaur information to kids.
        Finally, you mention that I should not even consider the
suggestion that birds are dinosaurs. As you may recall, I said I wanted to
leave it as an "option," not a given. I want the kids to understand that
some scientists believe that birds ARE dinosaurs, but that other people
think they are just related. Why should it be wrong to present both

Amado Narvaez
Media Specialist
Montgomery Knolls Elementary School