Archaeopterygid bird from China

[Karl Magnacca]

On 30 Mar 2005 at 13:40, John Grehan wrote:
> The location of the oldest fossil has no empirical content about the
> origin of a group. In the given example the older/generalized fossil may
> occur in China, but that does not, of itself, suggest or show that the
> group originated in that area before originating in another. It is
> possible, for example, that the group arose from a widespread ancestor
> that was in both locations, and the pattern of fossil distribution
> represents the sequence of subsequent differentiation (thus the ancestor
> might split into two descendant lineages, one of which happens to be
> more primitive/generalized and has an older fossil record).

That simply means that the oldest fossils haven't been discovered yet.
Since we can't ever know that we have the absolute oldest, each one that
is found is empirical evidence and the cumulative weight of that
determines support for the hypothesis of place of origin.

> But it seems to be that the location of the older fossils is 'evidence'
> only because one has already decided that this is what they mean in
> terms of origin (i.e. if one has decided that the location of the oldest
> fossils is empirical evidence for the center of origin then the location
> of the oldest fossils is evidence for the center of origin).

No, it is evidence because the definition of the origin of a group is
where the basal member(s) lived.  So, the place of origin is where you
will find the oldest fossils.  That doesn't mean that they have been
found, but you have to go on what you have.  If lots of old fossils are
found in the same place, then it's reasonable (though never certain of
course) to hypothesize that that place is the origin.  Of course, given
the spottiness of the fossil record and where things fossilized when, it
may well be that the place of origin may simply be "Eurasia" if they
were widely distributed.  But finding one in Europe and 20 older ones in
China when you have reason to believe the chances of fossilization and
discovery are equal (I'm talking theoretically), I think it can
considered empirical evidence for an origin in China.

Karl
=====================
Karl Magnacca, USGS-BRD
PO Box 11, Hawaii Natl. Park, HI 96718
"Democracy used to be a good thing, but now it has
gotten into the wrong hands."   --Sen. Jesse Helms