Re: seeking clarification on the cladism debate

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: <Dinogeorge@aol.com>
1:30 AM


> Well, not quite for nothing. When a species is given its own higher
Linnaean
> taxa, this usually indicates that it has a long independent lineage within
> the group it is classified in, something that is often useful to know

true

> and not
> entirely obvious if it simply appears in a cladogram or cladistic taxonomy
as
> a sister group to all the other clades in the group.

That is rather obvious IMHO. Just look at a cladogram of Mammalia when you
know that Monotremata, Marsupialia and Placentalia are alive and everything
else extinct long ago.

> Also, those monospecific higher taxa may in time acquire more occupants.

Or not. Or in 100 years. Why create empty names for hypothetical purposes?

----- Original Message -----
From: <Dinogeorge@aol.com>
8:31 AM

> I neglected to mention that I was referring to morphological distance
rather
> than temporal distance. We can't tell anything about temporal distance
from
> only one species, but we can certainly see that the species is very
distinct
> morphologically from its nearest relatives.

Just that there is no measure for morphological distance (which is why there
is no genericometer). Even when you use phenetics it doesn't really work.

> << And in practice, it's often difficult to tell whether something has a
long
>  or short independent lineage. Does _Archaeopteryx_' lineage, separate
from
>  other avians, stretch back to the Triassic (as Chatterjee would have it)
>  or merely to the early Late Jurassic? >>
>
> That doesn't matter. Archaeopteryx is wildly different from other birds
> [...] and, if
> you are into typological classifications, would require considerable
> taxonomic separation.

This sort of thinking is what I often see in classifications of basal taxa.
People discovered *Archaeopteryx*, decided it was a bird for reasons that
were totally obvious _at that time_, and _then_ said "Oh, _boy_, what a
_funky_ bird this is! It has teeth, free fingers, a tail and whatnot, it is
the most atypical bird ever seen! It deserves a whole new order, bah, what
do I say, a totally separate _subclass_ because it is just so weird!",
somehow implying it was the most _derived_ bird (derived away from the type,
not from the common ancestor). Today we know (dumb phrase, but sometimes it
fits) that *Archaeopteryx* is the least derived known bird and must be very
similar to the common ancestor. It is therefore the _most typical and least
unusual_ bird. Plus, we have now lots of "intermediates" between it and
Neornithes. To divide a Hennigian comb into two or more subclasses is...
difficult at the least.
        (Ignoring quarrels about whether it should be called a bird in the
first place, whether it is more similar to dromaeosaurids than to
pygostylians and so on.)