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Re: correct this "definition"



> I think this is a point that bears repeating: this is a diagnosis, not
> a definition. What makes a dinosaur a dinosaur is it being descended
> from (or identical to) the final common ancestor of _Iguanodon_,
> _Megalosaurus_, and _Hylaeosaurus_ (or something along those lines--as
> previously mentioned, there are a few minor variations on this
> definition). Diagnostic character states are something we use to
> figure out whether or not a given organism is descended from that
> ancestor. They help us to apply the definition, but they are not part
> of the definition.

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?

Answer: We don't want to be forced to call lots of critters
"dinosaurs" which somehow we don't want to be dinosaurs. And why?
Because we want dinosaurs only to include certain animals that we like
to think of as dinosaurs (and all their descendants as well) - for
historical reasons, Dimetrodon was not among those.

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

> To sum up: the diagnosis may fluctuate as new data comes to light, but
> the definition remains the same.

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? ).

Martin,

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


                   Priv.-Doz. Dr. Martin BÃker
                   Institut fÃr Werkstoffe
                   Technische UniversitÃt Braunschweig
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                   e-mail <martin.baeker@tu-bs.de>