RE: Ancestors [was: Re: And while on the theory of phylogenetic reconstruction...]

[Mike Milbocker <mmilbocker@psdllc.com>]

-----Original Message-----
Reading the below discussion it occurs to me that "basal" and "root" or
outgroup have quite different meanings. The character states of the root are
intended to be the primitive states that are changed through evolution, thus
the states that determine the cladogram structure are the derived states.
The states in the root taxon are essentially lost. Whereas,Michael Keesey's
comment on basal seems to suggest retained primitive states. For example,
bipedal being characteristic and retained in the dinosaurs. The root states
and the basal states, at least according to the discussion below, are almost
entirely mutually exclusive.

Regards,

Mike Milbocker


--- "Jonathan R. Wagner" <jonathan.r.wagner@mail.utexas.edu> wrote:
>     The real upshot is that the term basal ("at the base") implies some
form
> of unequivocal directionality in a tree. While a rooted tree does have an
> unequivocal "up" direction, i.e., time, this directionality is relative
> among branches.

And if it's time that you're talking about, you might as well use "early"
instead of "basal".

Good points. It does seem to me that there is still one area where the term
"basal" is useful, and that's in describing characters, e.g. "bipedality is
basal for _Dinosauria_", "hair is a basal trait for _Mammalia_", "ectothermy
is
the basal condition for _Amniota_", "monotremes retain the reproductive
system
of basal _Mammalia_", etc.



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