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Re: T-J Extinction event article (more media errors?)



In a message dated 5/12/01 4:39:39 PM EST, tmk@dinosauricon.com writes:

<< What I want to know is why you consider turning traditional taxa into 
stem-based clades more elegant than turning them into crown clades? >>

Crown clades are an accident: the (supposedly) fortunate lineages that 
happened to have survived to the present. Why should this be the criterion 
that determines where we cut off for Mammalia? By tradition, the amniotes are 
divided into three subtaxa: reptiles, birds, and mammals. Why not let each 
subtaxon extend as far down its phylogeny as possible, until it contacts its 
common ancestor with one of the other subtaxa? We already know that birds are 
themselves a subtaxon of reptiles, so let's let the reptiles and the mammals 
extend down to their common amniote ancestor. For that matter, we might even 
let reptiles extend all the way down to their common ancestor with 
amphibians, which would make mammals a reptile subtaxon, too. It's just as 
workable as any other scheme.