RE: The iguanodont paper

[Tim Williams <twilliams_alpha@hotmail.com>]

Eike wrote: 

> I would go as far as to say that from the point of
> evolutionary ecology, *most* paraphyletic groups are
> interesting.  

Unfortunately, paraphyletic groups can also be highly misleading.  People can 
mistake them for standalone groups in their own right, and make erroneous 
conclusions accordingly. 

Take the example of the old Dinosauria, which excluded birds. People made all 
sorts of sweeping statements, such as: "Dinosaurs never became aquatic or 
marine" and "All dinosaurs became extinct at the end of the Cretaceous".  We 
now know that both statements are untrue, and (more importantly) were *never* 
true, given that birds are a subset of dinosaurs.  But if we were to have a 
taxonomic group that was limited to the *traditional* dinosaurs (i.e., without 
birds), these clangers would return with a vengeance.  Ditto for "Thecodontia", 
and so forth.

Comparing a paraphyletic "Iguanodontidae" (= non-hadrosaur iguanodonts, or 
"spiky-thumb" group) with hadrosaurs is apples and oranges.  In evolutionary 
terms, hadrosaurs are a subset of iguanodonts.  There's nothing hadrosaurs have 
that wasn't either present in the "iguanodontids", or secondarily lost by the 
hadrosaurs (like the spiky thumb).  Thus, by saying that "iguanodontids" were 
at least as widespread or diverse as hadrosaurs is potentially misleading, 
because it is impossible to discuss the success of iguanodonts without 
including the hadrosaurs.

Cheers

Tim


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