On 04/12/2010 12:57 PM, andrel wrote:
> "Birds are dinosaurs, and dinosaurs (except birds) are reptiles, hence
> (sorry no hence)."

  Dinosaurs belong to the class reptilia, and theropods are a suborder
of dinosaurs, hence theropods are also reptiles. If birds were
theropods, they would obviously also belong to the class reptilia.

  I'm not sure where you are conjuring that "(except birds)" thing. Why
is it ok to say "birds are not reptiles" but not to say "birds are not
dinosaurs"? Why do you draw the line between dinosaurs and reptiles
rather than between birds and dinosaurs?

>>   If birds were - indeed - dinosaurs, that *would* make them reptiles
>> because dinosaurs are classified as reptiles. However, birds are *not*
>> classified as reptiles. Hence birds are *not* dinosaurs.
> 
> A good example why paraphyletic groups are not a good idea. It leads to
> logical inconsistencies like this.

  It's not a logical inconsistency. You simply say "birds are not
dinosaurs" and everything is consistent.

>>   Just because birds *evolved* from dinosaurs doesn't change that.
> 
> No, but changing definitions of what a dinosaur is might.

  But why do you want to change the definition of "dinosaur" rather than
keep the current definition of "bird"? Why do you want to cut the
relationship between birds and reptiles between the dinosaur-reptile
classification, rather than between the bird-dinosaur classification?
The latter would be much more logical.

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On 12-4-2010 15:07, Warp wrote:
> On 04/12/2010 12:57 PM, andrel wrote:
>> "Birds are dinosaurs, and dinosaurs (except birds) are reptiles, hence
>> (sorry no hence)."
> 
>   Dinosaurs belong to the class reptilia, and theropods are a suborder
> of dinosaurs, hence theropods are also reptiles. If birds were
> theropods, 

They are, so what is your point?

 > they would obviously also belong to the class reptilia.

Let me try to explain ones more.

There used to be a division of the amniotes in three classes Reptilia, 
Aves, and Mammalia. The fact that all reptiles ended up in one class was 
because people thought that mammals and birds were easily distinguished 
and all reptiles looked a bit the same.

This was all nice and neat until we learned that if you go back to the 
common ancestor of all reptiles that is also the ancestor of all mammals 
and birds. By convention there is still something as 'reptiles' that 
still don't include birds and mammals, but it has become a very messy 
(paraphyletic) group, whose name is preferably not used except 
colloquial. For a definition of dinosaurs people did not explicitly 
exclude the birds because the birds were in a different class anyway. 
Except that it turned out that birds were in fact dinosaurs and then it 
was to late to change the definition of dinosaur.
So the situation is rather messy now. All extinct dinosaurs that you are 
familiar with from the picture books are reptiles*. All living dinosaurs 
are birds, yet birds are not reptiles.

BTW I don't want to change any definition, I just try to explain what is 
to the best of my knowledge the current situation. Which differs 
considerably from what I learned when I was young.

Aside: for a number of reasons I have been looking at wikipedia at the 
family trees of the amniotes the last few weeks (this thread is only one 
of them). I can only conclude that ATM the articles are rather inconsistent.

*) except perhaps archaeopteryx and other more recently discovered 
dinosaurs that are grouped with the birds in Aves. But you could get 
away with that problem by redefining Aves to include only upto the 
common ancestor of all living birds and stopping all excavations of 
dinosaur sites.

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On 13-4-2010 17:00, Christian Froeschlin wrote:
> Christian Froeschlin wrote:
> 
>> In contrast, "non-avian monkey" gives no results ;)
> 
> Although it will once this post archives. Doh.
> 
possibly even three

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