[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
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
Ja. Hadrosauriformes and Iguanodontoidea are effectively the same
clade, albeit defined differently.
Hadrosauriformes = Least inclusive clade containing _Iguanodon_ and
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
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.
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