Dinosauria, as its currently understood, is monophyletic and useful to refer to; Thecodontia is paraphyletic and is not.
If you look at any given cladogram, count up the possible number paraphyletic groups you could name. ... I doubt anybody could argue that most of the groupings you could make are useful for anything at all. Paraphyletic groupings need to be chosen carefully and conservatively to have some utility.
Absolutely. I would not even consider most possible paraphyletic groups.
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