[Taxacom] Poor flying hoatzins dispersed (on flotsam) from Africa to S. America?

[John Grehan]

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Frederick W.
Schueler

> * presumably the underlying assumption is that there are other nodes
in avian phylogeny 
> that preclude the Hoatzins originating before the Atlantic opened.

I am not aware of other 'nodes' precluding anything.


>> 2) Hoatzins unable to fly long distances, and they say they've got
> evidence that this was the case for the fossils as well, and, of 
> course,
>
> Presumably, but that has no direct bearing on their being on both 
> sides of the Atlantic.

> * but if they originated after the Atlantic opened, and their
apomorphies for folivory 
> preclude strong flight, then they've got to have gotten across
somehow.

Right - IF. But the 'if' is not based on empirical data.


>> * remember that the widely accepted alternative that Darwin was
> arguing against *was* myriads of miracles, not plate tectonics.
>
> Is this explicitly stated by Darwin somewhere?

> * yes, the chapters on dispersal in the Origin are "one long argument"

> against the idea of some sort of scheme of in situ special creation.

I don't recall that he explicitly made this point in those chapters -
but then memory is not perfect. Either way, he excluded other
possibilities other than his belief in centers of origin and dispersal.

>> He was concerned to show that long distance dispersal was possible, 
>> because otherwise similar species couldn't be related by descent from
common ancestors.
>
> He did not have to appeal to means of dispersal, just as Hooker did
not.

> * what else was he to appeal to, in 1859?

Well, Hooker appealed to former land connections.

>> As with species concepts, his concerns, in the Origin, were very 
>> different from those we have now that descent with modification is
the underlying premise of biology.
>
> But the same dispersal model continues to be in vogue - virtually an 
> appeal to a set of miracles.

> * the whole point of dispersalist reasoning is that dispersal events
are not miracles,
> they're just very improbable,

They are often described as mysterious.

> but with many taxa available over long periods of time, they do in
fact happen. 

But in general in way that correlates with tectonics.

> With plate tectonics in place as a geological theory, all biogeography
is now basically 
> vicariant, 

Not according to the molecular dispersalists.

> and dispersalism is an exception to what's expected. 

It's the norm according to molecular dispersalists.

> It's hard to reason about rare events that don't leave direct evidence
of their 
> occurrence, and it's to temper the apparent miracles that such
scenarios as flotsam are 
> brought into the discussion.

Flotsam as the basis for dispersal looks little different to miraculous
to me.

John Grehan

fred.
------------------------------------------------------------
          Frederick W. Schueler & Aleta Karstad Bishops Mills Natural
History Centre - http://pinicola.ca/bmnhc.htm now in the field on the
Thirty Years Later Expedition -
http://fragileinheritance.org/projects/thirty/thirtyintro.htm
Daily Paintings - http://karstaddailypaintings.blogspot.com/
     RR#2 Bishops Mills, Ontario, Canada K0G 1T0
   on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
    (613)258-3107 <bckcdb at istar.ca> http://pinicola.ca/
------------------------------------------------------------
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