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re: Ankle Articulation in Pterosaurs

Amado Narvaez <anarvaez@umd5.umd.edu> wrote:

>A while back I posed a question about pterosaur characteristics that
>separate them cladistically from dinosaurs. 

        Can of worms alert!
        There is an article in the new JVP ( vol 16, number 4, I believe...)
by F. Novas on dinosaur monophyly which has some material on pterosaurs.  I
have heard tell of other articles which suggest that the two are not even
closely related.  Anyone with references, please post!
        You should note that, in cladistics, characters do not separate
taxa, they only suggest and support phylogenetic propinquity.  On the same
vein, characters are not necessarily diagnostic of a clade, as the addition
of new material to the data matrix can affect the character distribution.
In plain english, the characters do not make the clades, and you can't
always say that what you observe in a new specimen makes it a member of a
certain clade, as the new specimen might actually alter the dynamics of your

>Would this "digitigrade position of the foot" be a dinosaur/bird trait
>that would be useful in explaining to laypeople (myself included) why
>pterosaurs cannot be included among the dinosaurs?

        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.  

>(I don't want to use the "dinosaurs lived only on the land and could not fly" 
>rationale because I want to leave open the option of including birds among the

        Forgive my vehemence, but you should not want to use this because it
is not correct.  As scientists (and educated non-scientists), it is our
responsibility to teach the public, not to give them simple answers to
complex questions.  Once properly prepared, lay people can deal quite well
with science, but only if we let them.

        Good luck,
| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |