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Re: Ceratosauria vs. Neotheropoda?



> Nein, nein, nein. Hadrosauriformes are not a subset of iguanodonts,
> both are subsets of iguanodontoids.

Doch. Iguanodontia is a pretty huge clade that includes almost all known ornithopods.

 Ja.  Hadrosauriformes and Iguanodontoidea are effectively the same
 clade, albeit defined differently.

 Hadrosauriformes = Least inclusive clade containing _Iguanodon_ and
 _Parasaurolophus_.

 Iguanodontoidea = _Iguanodon_ and all iguanodontians more closely
 related to _Edmontosaurus_ than to _Camptosaurus_.

I hope this means "everything more closely related to *Iguanodon* and *Edmontosaurus* than to *Camptosaurus*"? That would be a branch-based definition and could apply to a (somewhat) larger clade than the definition of Hadrosauriformes.

(Interestingly, if I'm right, the name Iguanodontoidea would self-destruct if *Camptosaurus* ever showed up inside the smallest clade that contains *Iguanodon* and *Edmontosaurus*. Not that I think that'll ever happen, though.)

> What we have now is a situation in which your hadrosaurs have
> series of formal names pertinent to them alone because of the
> accident of their being derived within the clade, while the more
> basal iguanodontoids are stuck with no formal designation because
> doing so would result is gasp and horror paraphyletic groups which
> are phylocode evil for no good reason.

There are very good reasons. Here's one off the top of my head:

All those biodiversity studies from Jablonski to Benton. They count genera, families, or even orders and then use those numbers in the assumption that they represent any kind of approximation to a measure of biodiversity. That simply isn't so. Orders, families, and even genera* are simply not countable. One reason for that is that they don't need to be monophyletic. In what sense that has anything to do with biodiversity do a paraphyletic family and a monophyletic one make two? Who decides which paraphyletic groups to recognize and which not? What other than laziness stops me from taking your Iguanodontidae and making Iguanodontidae, Mantellisauridae, Dollodontidae and presumably Ouranosauridae out of it? What other than laziness stops me from merging Hypsilophodontidae and Camptosauridae into your Iguanodontidae? (...Didn't *Hypsilophodon* even start out as an iguanodontid?)

Here's another: Why can't we recognize a group for egg-laying synapsids (an example that comes up on this list every few years) if that's interesting in the context of our ecological question? Only because it would overlap with Mammalia, never mind the paraphyletic Reptilia, and we can't have overlapping taxa in rank-based nomenclature. Names for monophyletic and paraphyletic groups block each other in that system; some of each require that some of the others must be dropped and their taxa must lack a recognized name. I think this would happen with your Iguanodontidae and Hadrosauriformes if someone gave Hadrosauriformes a rank. The trick is: "nothing in biology makes sense except in the light of evolution", "nothing in evolution makes sense without a good phylogeny" (Gina C. Gould & Bruce MacFadden, 2002, 2004) -- we actually _want_ to talk about phylogeny, and that only works if we can name every clade we find interesting, without names for grades getting in the way. This is probably the most important reason why the PhyloCode doesn't allow paraphyletic taxa to have an official name-definition combination.

When was the last time I posted the references to the Phylogenetic Diversity Index? Two months ago? Three maybe?

* Mesozoic dinosaur genera are, of course, very close to being countable. Arguably even more so than their species are.

> Having just finished up the dinosaur field guide I cannot
> overemphasize how this is a taxonomic mess that will befuddle the
> public.

Better confuse the public than mislead it.

 The "taxonomic mess" is solely a consequence of trying to translate a
 cladogram into a rank-based classification.

Exactly.

Why bother making classifications at all? Just print the tree, tie labels to defined places on the tree, and then you can talk about the clades the labels indicate. That's phylogenetic nomenclature. Could not be easier.