>Presumably the panclade name would be _Pan-Opisthocomus_ or >pan-Opisthocomus or something along those lines. It would be >permissible, e.g., to define _Opisthocomus_ as "_Opisthocomus hoazin_ and >all of its descendants".
Wouldn't this be a tautology?
Only if _O. hoazin_ goes extinct before giving rise to other species....
>Alternately, you could use _Opisthocomiformes_ for the total group.
Yep, this is my favourite option. Trouble is, like I said, as well as having _Opisthocomus hoazin_ as the internal specifier, you would have an extremely long list of external specifiers. You would probably need a representative of almost every other extant neognath 'order' as an external specifier, to cater for any and all topologies of modern bird phylogeny.
Not true: "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."
-- Mike Keesey