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Re: correct this "definition"



On Thu, Apr 17, 2008 at 2:37 AM, Martin Baeker <martin.baeker@tu-bs.de> wrote:
>
>  I know we've been there ever so often and all got the T-shirt and
>  everything, but - although I scientifically understand what is meant
>  here - I think this will be confusing to laypeople for the following
>  simple reason: *Why* is this the definition of dinosaur?  Why did we
>  choose these two critters and say: "They make up what is a dinosaur"?
>  Why not include plesiosaurs, Dimetrodon or all the other cool extinct
>  critters? Who is the one who gets to make up the name?

Sir Richard Owen is. :)

>  To cook up an example, if we define Dinosaurs=(Iguanodon+Megalos.) and
>  if we would later discover that Sauropods are not part of this clade
>  (improbable, sure, but it's just an example), what would happen?

Not a bad question. It would come down to deciding whether to favor
the original usage (which specifically excluded the only sauropod
known to the author) or the historical usage (which has pretty
consistently included sauropods). I suspect people would opt for the
latter, but it is a bit of a toss-up. (Thank goodness we almost
certainly will never have to actually face this dilemma!)

>  Or imagine we would use the definition dino=(passer+Iguanod.), and we
>  would then find out (improbable again) that the BANDITs were right,
>  would we then accept that lots of other critters are also dinosaurs
>  and stop using the term cause it is useless,

This is why the PhyloCode expressly recommends against such a
definition: http://www.ohiou.edu/phylocode/art11.html#rec11a-example1

>  or would we re-define?  (Of course, if Phylocode were enabled, we couldn't).

Yes, we could, under the latest draft:

"15.11.  An unrestricted emendation (see Art. 15.8) is intended to
preserve the application of a particular name in terms of the
conceptualization of the clade to which it refers. Unrestricted
emendations may involve changes in specifiers or qualifying clauses
but must retain the same definition type (node-based, branch-based, or
apomorphy-based), the same clade category (i.e., crown clade, total
clade) if category was specified in the protologue, and the same clade
conceptualization as interpreted from the protologue."

More here: http://www.ohiou.edu/phylocode/art15.html#art15.11

(The concept of "restricted" and "unrestricted" emendations follows
from Sereno's idea of "first-order" and "second-order" revisions.
Restricted emendations are more drastic, and require approval by the
CPN.)

>  But the definition in itself reflects some understanding of data at
>  some time, and these data are based on diagnoses. Saying what are
>  dinosaurs is determined "by definition" does not explain how this
>  definition came to be, and surely that's what people want to know
>  (*Why* are Dimetrodons and Mammuts not dinosaurs? ).

That'd certainly be an interesting area to go into, but would the full
history of the name be appropriate for a general talk on dinosaurs? I
suppose you could say the original diagnosis partly holds up and
partly doesn't, and that's why the definition is based on the original
composition, not the original diagnosis. But I dunno who'd still be
awake after that. :)

>  who hipes that this does not start of the next clade war (and please
>  note that I nowhere say anything against cladistics...)

Not at all! This is about nomenclature, not analysis. (And nowhere
here have you recommended giving a paraphyletic group a name like that
of a clade.)
-- 
T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039
http://exopolis.com/
--
http://3lbmonkeybrain.blogspot.com/