Archaeopterygid bird from China

[John Grehan]

> Behalf Of Karl Magnacca


> That sounds like a geographically restricted center of origin to me.

'Restricted' is a relative term. I was using in relation to the total
range. To postulate that archaeopterygids originated in one part of the
total range is to invoke a restricted center of origin. I argue that it
is not an empirical necessity.

> This is the problem with your whole argument: it's against blind
> adherence to theory, and Darwin's original faulty logic, not against
> this case.

This case is a derivation of the theory. If one did not already believe
in Darwinian centers of origin one would not invoke one for this case.

> I don't think this is true.  It seems to me that most biogeographers
> since the 1970's have stuck tightly to vicariance as the main mode of
> evolution.  Dispersal is out of fashion.  Get with the program, man!

I don't think I am that stupid (although one never knows). In our
panbiogeography book I and my colleagues did point out that there was a
broad adoption of a vicariance mode of reasoning. However, much of the
vicariance reasoning is still Darwinian in that they often appeal to a
center of origin followed by dispersal before the appearance of a
barrier so its just dispersalism before the barrier as opposed to
dispersalism after. Now there are people like Keven de Queroiz (in TREE
- a journal that appears to have an editorial leaning towards Darwinian
dispersalism), and editors such as Chris Simon who argue that vicariance
is totally discredited by molecular clock theory (another case of theory
over-riding the empirical world) and there is a resurgence of
dispersalim as the [popular the current mode of biogeography! If that's
the 'program' I'm happy to be outside!

It was based on - I know this is going to be a shocker - empirical
evidence,
> i.e. the distribution of fossils.

Please show me how the fossils are empirical evidence of a center of
origin and that I am wrong to assert that the distribution of fossils
are simply the distribution of fossils.

> If this happens, then you will find all of them distributed across the
> entire area from the start.  

Not true.

If, somehow, the first archaeopterygid
> lived all the way across Eurasia, you would expect to find them in the
> entire area at the same time.  Thus the entire region is the center of
> origin.

Now that I have no problem with!

Finding a diverse array of fossils in one area, and few to
> none elsewhere (and those being later), seems to me to be empirical
> evidence that the group originated in that area and had its first
round
> of diversification there.  

This appears to be the nitty gritty. If it were empirical I would agree
with you, but it's a theoretical interpretation of the distribution of
fossils that leads one to reason a restricted center of origin - not the
other way around. As you say - "it seems to me to be empirical.." -
seems? If it only seems to be, then that suggests to me that it is not
empirical.

There's no theory involved; whatever Darwin
> would think is irrelevant.  

Perhaps, but his thinking has influenced a lot of biogeographers.

No it's not conclusive proof, but you're
> never going to get that (especially with fossils).  It's a matter of
the
> evidence at hand.

As argued above, it is not evidence at hand - its theory.

John Grehan