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Re: The Papers That Ate Cincinnati

On 5/6/07, Tim Williams <twilliams_alpha@hotmail.com> wrote:

>Only if _O. hoazin_ goes extinct before giving rise to other species....

I think the point at which the hoatzin has given rise to other species, us
_Homo sapiens_ would be long gone.  :-(

I dunno, vice versa seems more likely to me.

(Anyway, yes, defining _Opisthocomus_ as the crown clade stemming from
_O. hoazin_ might be forward-thinking to a fault.)

>"Let C be the clade consisting of _Opisthocomus hoazin_ and all
>descendants thereof. _Opisthocomiformes_ is defined as the first
>ancestor of _O. hoazin_ (and hence of C) which is not also ancestral to any
>extant organism outside of C, and all of that first ancestor's

OK, that should work quite well for _Opisthocomus_.  Opisthocomiformes would
effectively be the same as Panopisthocomiformes.

Well, _Pan-Opisthocomus_, if _Opisthocomus_ is a crown clade. See Article 10.3 for the current proposal on panclade names: http://www.ohiou.edu/phylocode/art10.html (Although this may be somewhat emended in the next version--we'll see.)

The only potential problem (and it may not be much of a problem, except
maybe in an aesthetic sense) is if all bird 'orders' are defined in such a
way.  For example, what would happen if the hoatzin is suddenly found to be
nested inside another bird 'order' (like Cuculiformes)?

I think that's absolutely fine. In mammals, _Cetacea_ is part of _Artiodactyla_. In insects, _Isoptera_ is part of _Dictyoptera_ and _Siphonaptera_ is part of _Mecoptera_. If opisthocomiforms are cuculiforms, great. We've learned something new and the nomenclature can help communicate that.

My concern is that with modern bird phylogeny being in flux, certain
traditional 'orders' may emerge as paraphyletic (some already have) and
therefore contain other bird 'orders'.  I have nothing against this per se,
since ranks (such as 'orders') are arbitrary anyway.   But it could all get
very 'messy' - as I said, an aesthetic problem, not a substantive one.  One
solution is to junk the "-iformes" suffix altogether, and abolish all the
baggage of the Linnaean ordinal classification of birds.

Well, birds are already part of _Dinosauriformes_, which is part of _Archosauriformes_....

I think the -iformes names are too common and useful to abandon. We
just have to get used to the idea that one may contain another. (Much
as, for pterygote insects, a -ptera may contain another -ptera.)

If you reeeeeeeeally wanted them to be exclusive, though, you could do this:
1) Create a finite set, S, of ordinal type species: _Struthio
camelus_, _Tinamus major_, _Passer domesticus_, _Gallus gallus_, etc.
2) Define an -iformes name based on the genus name of each species as
follows: "X-iformes is the last common ancestor of all extant species
sharing closer ancestry with [type species of X] than with any member
of S that is not [type species of X], and all descendants of that

But this would have some undesirable outcomes. For one, if
_Opisthocomus hoazin_ is one of the species in S, then
_Opisthocomiformes_ = _O. hoazin_ (possibly). No fossil organism could
possibly belong (under some topologies, anyway).

For another, _O. hoazin_ bouncing around the phylogenetic tree might
wreak havoc on our usage of other clade names. Some "families" might
find themselves without any "order" (which is not a terrible thing,
but you might not find that "aesthetic", either). And, for example, if
it is related to crotophagids, then _Cuculiformes_ would become very
restricted, including only cuculids. Finally, which statement would
better reflect its new position, "_Crotophagidae_ and
_Opisthocomiformes_ are synonymous," or, "Opisthocomiforms are
crotophagid cuculiforms"?

Mike Keesey