Re: The Papers That Ate Cincinnati

["T. Michael Keesey" <keesey@gmail.com>]

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
> >descendants."
>
> 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
ancestor".

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