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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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