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

[Frederick W. Schueler]

On 10/10/2011 12:41 PM, John Grehan wrote:
> From: taxacom-bounces at mailman.nhm.ku.edu
> [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Frederick W.
> Schueler

>> * but it is based on empirical evidence: 1) Hoatzin fossils on both
> sides of the Atlantic,
>
> All that tells you is that the clade was on both sides of the Pacific by
> a particular date at the MINIMUM. Nothing about dispersal.

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

>> 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. I'm not saying I'm enamored of this, just 
that it's a train of reasoning 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.

>> 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?

>> 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, but with many taxa available 
over long periods of time, they do in fact happen. With plate tectonics 
in place as a geological theory, all biogeography is now basically 
vicariant, and dispersalism is an exception to what's expected. 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.

fred.
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          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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