[Taxacom] Poor flying hoatzins dispersed (n flotsam)

[John Grehan]

Heads has already commented on the nature of these imagined dispersal events being unique rather than rare. As for surviving the Cretaceous extinction, 'specialized' or not, the spatial correlation of distributions and tectonics does indeed suggest that many taxa survived the end of the Cretaceous and leave their biogeographic mark in the present. 

John Grehan


-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman
Sent: Tuesday, October 11, 2011 11:19 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Poor flying hoatzins dispersed (n flotsam)

Hi All,
?? ?????It seems that John Grehan is so excessively vicariance-oriented that he wants to explain away rare dispersal events in any way that he can, branding them as "far-fetched" or even "fantasies" and even comparing the scientists proposing such events to creationists. So I would bounce back his initial comment "Good Grief"
right back at him.
?? ?????Anyway, flotsam from North America explaining some

Caribbean biological distributions seems a perfectly valid hypothesis, on the scale of million years (or even less). And rare longer distance flotsam events over tens of millions of years seems a reasonable
hypothesis as well. ? ? ?      ? 
?? ????Frankly I think that the power of two major tsunamis in just the last decade (off Japan and earlier off Sumatra) is just a hint of how devasatating those (or even larger forces over geological time periods) can be in sweeping large masses of flotsam (perhaps even thousand of trees on rare occasions) into the ocean as the water retreat. Then it just takes favorable currents to occasionally sweep some of them to another continent.
????????A large clump of hundreds of trees (or perhaps even just a few dozen trees for that matter) carrying a colony of hoatzins from Africa to South America in one rare event does not seem a fantasy at all. As long as the trees had leaves to munch on (better yet some fruits as well), such vegetarians could no doubt get by for weeks, if not months, until they reached South America. It doesn't seem far-fetched to me, and it only had to happen once.
????????Seems just as likely to have happened once as John's alternative explanation that hoatzins evolved extremely early (Late Cretaceous??) in a connected Africa-South American region. So where is the evidence that hoatzins have been around that long? And I especially have a hard time imagining a specialized and tree-dwelling bird like the hoatzin surviving the devastation of the end-Cretaceous extinction (unless it was perhaps geographically much further removed, as in Australia). Therefore, a Cenozoic tsunami-flotsam event seems a lot more survivable, landing in South America with plenty of luxurious Cenozoic vegetation to eat upon arrival, as opposed to the fire-storms that must have devastated the forests of the Americas at the end of the Cretaceous.  
      Calling such a dispersal a fantasy or even far-fetched seems to underestimate the potential of rare, massive, forces of nature to exceed

our expectations in dispersing taxa in ways that were previously totally

unexpected.  And one could easily argue that it is sometimes proposed vicariance (especially in the crocodile case) which is far-fetched.
Vicariance has its place, but to invoke it excessively can be
counterproductive.            
????????????????---------Ken Kinman          
--------------------------------------------------------           
John Grehan wrote:
     The funny thing is that these sorts of 'far fetched' stories have been the popular mode for biogeographers from the time of Darwin. 
The recent popularity among molecular clock theorists is only the latest

phase of this way of thinking which avoids the unpleasant necessity of biogeographers actually knowing some biogeography and actually knowing the comparative details of distribution (although even vicariance biogeographers are not immune from that distaste). 
In some ways the dispersalist focus on unique dispersal events is like a

systematist who makes a phylogeny on the basis of a single character without bothering to look at any other characters.



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