[Taxacom] Hedges /Kumar (eds) The Timetree of Life

[Michael Heads]

Hi Jason,
 
 
 
I looked up hystricognath rodents in the Timetree book. The group is a classic biogeographic 'problem', with the New World caviomorphs sister to the African phiomorphs. The oldest fossils of both caviomorphs and phiomorphs are c.37 Ma. The text states: 'Consequently, these dates are congruent with the hypothesis that the invasion of South America by African hystricognath ancestors involved overwater waif dispersal across a 1700-km expanse of the Atlantic subsequent to the separation of these two continents at a much earlier date'.
 
   But if the dates are treated as minima, they are just as congruent with vicariance as they are with dispersal. The reason the author does not mention vicariance is that the dates are being treated as maxima. The authors says the group evolved 'subsequent to' the opening of the Atlantic. This means that the date proposed is being treated as a maximum. If it were being treated as a minimum, the author wouldn't have said it evolved 'subsequent' to anything, he would only have been able to say it evolved 'before' such and such a date or event. Further on, the author says that the opening of the Atlantic was 'at a much earlier date' than the origin of the group. Again, the date, which is an estimate of minimum age, is being treated as an estimate of maximum (absolute) age. 
 
Michael Heads
 
 


Wellington, New Zealand.

My papers on biogeography are at: http://tiny.cc/RiUE0

--- On Tue, 17/5/11, Jason Mate <jfmate at hotmail.com> wrote:


From: Jason Mate <jfmate at hotmail.com>
Subject: Re: [Taxacom] Hedges /Kumar (eds) The Timetree of Life
To: "Taxacom" <taxacom at mailman.nhm.ku.edu>
Received: Tuesday, 17 May, 2011, 7:17 AM



John,

criticism is fair game as long as you back it up with facts. If you have read any of the articles (i.e. Hepialids) point at the problems you see. But deriding all books that use or rely on molecular data as propaganda
is just boring. You may have good points but you are just not fleshing them out.

As for the use of fossil evidence, I have yet to come across a case were they use them as maximal age when dating trees. It just makes no sense to state that you have the fossil of the very first 
exemplar of a taxon.

Best

Jason

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