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Re: Non-serpentine lacertids (was RE:WHAT'S GOING ON?)



<It is never natural to remove a descendent from a supraspecific taxon.
Removing birds from Dinosauria, in my view, makes as much sense as removing
ceratopsians or stegosaurs.>
OK, I think I'm getting the naming rule you're using.  Any group descendant
from another group within any supraspecific taxon should not be removed.

The reasoning, though, is a bit confusing:
< The group exists regardless of our perceptions...  By setting an upper
bound, we change these ontological
individuals into classes of objects defined by some arbitrary set of
characteristics.  Since evolution does not create fixed classes, taxonomic
schemes relying on classes are not natural.>
If I'm following, creating a named group would exclude species which should
evolutionarily be included based on some further rules for inclusion.  Any
group identified by anyone will exclude direct ancestors which are part of
another group, as you're saying.  However, if 'real' (evolutionary) group
were to equal 'named' group, wouldn't that be acceptable (natural)?  I think
you'd answer that because the group is wholly enclosed within another group,
separating it does not correspond to an <important> evolutionary dividing
line, but I want to be sure.
I would also appreciate understanding why descriptive purposes should be
rejected when such would not create a false picture of either the animals or
evolution.  (I suppose I'm working to be comfortable with the idea that
calling birds a group would be 'unnatural'.  It sure is intuitive.)
These are different terms of discussion from prior ones, so I'm trying to
establish the connections.
Thanks again!


----- Original Message -----
From: "chris brochu" <cbrochu@fmnh.org>
To: <dinosaur@usc.edu>
Sent: Monday, July 03, 2000 1:59 PM
Subject: Re: Non-serpentine lacertids (was RE:WHAT'S GOING ON?)


> ><Had we chosen to keep birds and nonavian dinosaurs separate, we would be
> >erecting a nonnatural group by arbitrarily removing those things with
> >unambiguous feathers from Dinosauria.>
> >
> >I'm not sure what you mean here.  You said earlier:
> ><The names are always arbitrary - this is true for all nomenclatural
systems
> >ever devised.  But in the phylogenetic system, the groups are not
arbitrary
> >- they exist (or at least are hypothesized) and are united by common
> >ancestry, whether we choose to name them or not.>
> >Birds are a group:
> >< Birds are still in their own group (Aves) - that this
> >group is a member of Dinosauria does not change the distinctiveness of
Aves,
> >any less than making Aves a member of Vertebrata.>
> >so why would 'removing' them be unnatural compared to 'removing' any
other
> >descendant group?
> >
>
>
> It is never natural to remove a descendent from a supraspecific taxon.
> Removing birds from Dinosauria, in my view, makes as much sense as
removing
> ceratopsians or stegosaurs.  Ceratopsia and Stegosauria are distinct taxa,
> but are internested within Dinosauria (as is Aves).
>
> There is a difference between a group of taxa and a name applied to that
> group.  The group exists regardless of our perceptions; we are limited by
> our imperfect means of discerning groups, but assuming our estimates of
> phylogeny actually reflect evolutionary history, the tree represents real
> individuals.  By setting an upper bound, we change these ontological
> individuals into classes of objects defined by some arbitrary set of
> characteristics.  Since evolution does not create fixed classes, taxonomic
> schemes relying on classes are not natural.
>
> I've posted some references on this issue in the past; you should be able
> to pull them up on the archive.
>
>
>
>
>
> >Also, I'm wondering about your use of the term 'unambiguous feathers'.
Are
> >you saying that feathers (not sure how 'unambiguous' is defined or used)
are
> >diagnostic of birds by themselves, without regard to other characters?
> >Thanks!
>
> No - that was just a quick example pulled from my head.  Groups of birds
> are surely diagnosed by more than feathers, and in any case feathers are
> not limited to members of Avialae.
>
>
> chris
>
>
> ----------------------
> Christopher A. Brochu
> Department of Geology
> Field Museum of Natural History
> 1400 S. Lake Shore Drive
> Chicago, IL 60605
>
> voice: 312-665-7633
> fax: 312-665-7641
> electronic:  cbrochu@fmppr.fmnh.org
>
>