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Re: Are Birds Saurischian?



   I'm not a paleontologist, and I don't play one on TV.  What follows is my
own, uneducated opinion.  So, consider what you paid to get it.

>Looking at the sample cladogram on page 34 of 
>the magazine, it looks to me like Archaeopteryx is a saurischian 
>dinosaur. If so, is it correct to say that all birds are saurischian 
>dinosaurs?

   As I understand cladistics, yes.  Anything connected to a certain node
carries that name.  This includes nodes that come later in the tree, but can
be traced back to that certain node.

 1   2   3
 \   \   /
  \   \ /
   \   *  Theropoda
    \ /
     * Saurischia
    /
   * Dinosauria

   where 1=Sauropoda, 2=Dromaeosaurs, 3=Aves (birds)

   Everything above Dinosauria is in the Dinosauria, everything above
Saurischia is in the Saurischia, everything above Theropoda is in the
Theropoda.  Therefore number 3, Aves, is a member of Theropoda AND
Saurischia AND Dinosauria.  However, number 1, Sauropoda, is only in the
Saurischia and Dinosauria since it branches off before the Theropoda.

   Note:  this is an example of a cladogram, and not intended to be mistaken
for the actual Dinosaurian cladogram.

>(I suppose what I'm asking is: If birds are dinosaurs, are 
>they a third basic group, or are there still only saurischians and 
>ornithischians, and birds belong completely in the former?)

   Birds are considered saurischians, specifically Theropods, under cladistics.

>And if birds 
>ARE saurischians, then only ornithischian dinosaurs became extinct, right?

   Yes.

   Now, if somebody adhere's to Linnean groupings, the answer to whether
birds are dinosaurs might be different.  However, from what I understand,
many paleontologists would consider birds dinosaurs even under Linnean
groupings.

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