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Re: TETRAPODS, PHYLOGENETIC TAXONOMY, AND CLEAR DEFINITIONS



>Thomas R. Holtz, Jr. wrote:
>
>> I'll try and keep this one brief.
>
>So will I.  Why does it seem that certain people on this list are incapable of
>comprehending simple English?
>
>> >Would it?  If the diagnosis of Dinosauria is as you state, then an animal
>> must have
>> >both those features to be a dinosaur.
>>
>> Ankylosaurs don't have a perforate acetabulum: they must not be dinosaurs
>> under your rules.
>
>I said **IF**, didn't I?  See, right there: "If the diagnosis of
>Dinosauria is as
>you state, then . . ."  The presence of the word "if" makes the statement a
>conditional one: _if_ X is true, _then_ Y follows.
>


But the IF is irrelevant, because perforate acetabula DO diagnose
Dinosauria, and ankylosaurs ARE dinosaurs.  This is why character states
are useful for diagnoses, but lousy for definitions.


chris



-=--=--=--=--=--=--=--=--=--=
Christopher Brochu

Postdoctoral Research Scientist
Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL  60605  USA

phone:  312-922-9410, ext. 469
fax:  312-922-9566

cbrochu@fmppr.fmnh.org