dispersal fantasy

[W.Wuster]

John Grehan wrote:

[comments on Raxworthy et al. bobbitted]

> Of course the authors use the propaganda tool of asserting the geological
> narrative is "well documented", but its still a story. They also appeal to
> dispersal by accepting the precedence of their 'molecular' clock
> reconstructions that are also incongruent with the postulated geological
> ages of the areas occupied by the lizards. They do not bother to consider
> that they may have novel evidence that the geological age is wrong.

Interesting point. There is in fact a recent paper by McCall (1997) in
Proc. R. Soc. Lond. B 264: 663-665, entitled "Implications of recent
geological investigations of the Mozambique Channel for the mammalian
colonization of Madagascar", which points out the probable existence of at
least stepping stone islands, and possibly even a fill landbridge, between
Africa and Madagascar in the Pleistocene. The abstract is reproduced here:

"Madagascar separated from continental Africa during the break-up of
Gondwanaland early in the
Cretaceous. The presence of several terrestrial mammalian groups on
Madagascar is paradoxical as (i)
these groups postdate the departure of Madagascar from Africa; and (ii)
terrestrial mammals are poor
dispersers across wide water barriers. Recent geological studies focusing
on the Davie Fracture Zone of the Mozambique Channel offerr a resolution to
this situation, by suggesting the presence of a land-bridge from the
mid-Eocene to the early Miocene, an interval that matches the ages of
Madagascar's mammalian groups".

One could argue that the chameleon story provides further support for this
hypothesis, and I find it surprising that this paper was not mentioned in
the Nature paper.

Cheers,

Wolfgang Wüster


--
Dr. Wolfgang Wüster  -  Lecturer
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