[Taxacom] Madagascar (was: Timetree of Life)

[John Grehan]

This is like having it always and any ways that makes the choices entirely meaningless. In other words, Ken is saying that dispersal explains everything - it explains where things are and it explains where things are not. If they are there - then they got their by dispersal. If they did not get there, then obviously they could not disperse. Like saying that Hystrichomorphs could jump the Atlantic, but could not jump across a much shorter distance from Borneo while other rodents could. Or various groups could not get to Madagascar (Simpson's disappointed ticket holder) while others obviously could. Or Pteropus bats could cross the Indian Ocenan, but could not cover the distance from offshore islands to mainland Africa or get to New Zealand. This sort of reasoning in biogeography produces meaningless nonsense.

While one may believe that it is 'extremely unlikely' that lorises and lemurs split before the K/T boundary, this belief alone has no necessary information content in that regard. On the other hand, the outlines of primate biogeography do show correlations with Mesozoic geology. Once again, it's a panbiogeographic analysis that led to the discovery of that fact, not dispersal theory.

Competitive exclusion has been dismissed a long time ago by mammalogists in Australia as an 'explanation'. In terms of general biogeography it may just be a reflection of an original vicariant differentiation of placentals and marsupials

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman
Sent: Wednesday, May 18, 2011 12:21 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Madagascar (was: Timetree of Life)

Hi Michael,
       Well, the lack of Hystricomorpha, Sciuromorpha, and various other
taxa in Madagascar would be most parsimoniously explained by the
difficulty and rarity of dispersal from mainland Africa to Madagascar.  
        It is probably largely by chance that lemur ancestors floated
over on trees.  However, such dispersal is not so unlikely that I would
turn to a vicariance explanation for lemur origins.  It seems extremely
unlikely to me that lorises and lemurs split before the K-T extinction.  
            ----------Ken               
P.S.  The lack of certain rodent taxa in Australasia may be due to a
more complex combination of factors, but competitive exclusion is one
likely factor in such taxa attempting to island-hop into that area
(perhaps more so than the isolation afforded by the Wallace Line).                                           
---------------------------------------------------------
Michael Heads wrote:            
     The trans-Atlantic pattern can be approached in the broader context
of the main rodent clades. It has to be explained together with
the fact that Hystricomorpha are not in Madagascar and are east
only to Borneo (cf. strepsirhines), while Sciuromorpha (squirrels) are
not in Madagascar and east only to Sulawesi (cf. haplorhines). Many
authors have commented on the absence of these groups from both
Madagascar and Australasia (cf. woodpeckers etc.). An
overall dispersal account for the rodents doesn't really explain
these interesting eastern limits in two of the three main rodent
groups, or their repetition in the primates and others.   



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