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Re: Tetrapod note (was: Re: [Re: Resting Sauropods])
Jonathan R. Wagner wrote:
> At 10:47 PM 7/17/98 -0400, Jonathon Woolf wrote:
> >"Recently, Tetrapoda was formally defined as a crown-group (Gauthier et al.,
> >1989).A crown-group is a clade that includes the last common ancestor of two
> >more extant taxa, and all its descendants. In this case, Tetrapoda was
> >as the clade that includes the last common ancestor of lissamphibians and
> >amniotes, and all its descendants."
> This definition is specifically *not* the definition I was referring
Sorry. I thought non-cladistic definitions had been outlawed on this list.
> Hopefully this hasn't confused any more people out there too much. Let
> me try to seperate the Tetrapod thing out for everyone:
> Connotations/definitions/invocations of "tetrapod":
> a) "A four legged animal" or "an animal that walks on four feet"
> b) "All animals which share a four limbed heritage" [my wording]
> c) "The most recent common ancestor of Lissamphibia and Amniota and all
> its descendants."
> Definition (a) is the "common sense" definition, and I'm not sure that it is
> commonly used in science, since tetrapod (lower case "t") seems to carry the
> strong taxonomic and/or evolutionary connotation. That connotation is most
> liberally summed up by definition (b). Definition (c) is an explicit
> definition of a phylogenetic taxon (the "cladistic" connotation others have
> referred to). Do not confuse (b) and (c).
a) is the _literal_ definition, being a literal translation to English of the
word "tetrapod." b) is probably the most common definition in informal
usage, and the one that makes the most sense for the context of paleontology.
Definition c), as you point out, is the cladistic one, and the cladists can
for all I care. Any definition that says _Seymouria_ isn't a tetrapod has no
rational basis as far as I can tell..
> There is a taxonomic quandry here.
Yeah, those turn up a lot when cladists get loose. Funny thing, that -- almost
seems to be saying there's something wrong with either the methodology or the
it's being applied. Scientific tools and methods are supposed to reduce
not increase it.
-- Jon W.