[Taxacom] Dispersal paradigm (was: Antarctic dispersal)

[Michael Heads]

Hi Ken,

The Mitchell study of the Anas ducks was calibrated with a Miocene fossil,
A. soporata. As for its identification, the authors wrote: 'Based on its
plesiomorphic morphology, we judged A. soporata to be an outgroup to extant
Anas'. No other details were given. But they admitted: 'We consider Anas
soporata to be a stem member of the genus; however, if this interpretation
is incorrect and A. soporata is in fact crown-Anas then this would lead us
to underestimate divergence dates'. So that's one real problem - placing a
fossil at a precise point on a phylogeny.

One other problem is: just how much older than the fossil can the clade be?
Mitchell et al stipulated, as a prior, that the group with the Miocene
fossil could be no older than the exact base of the Oligocene (33.9 Ma).
But why pick that age? Why not 34.0 Ma? Why not the middle of the Eocene,
or the base of the Eocene, or the Paleocene, or the Cretaceous...? There's
no reason, it's completely arbitrary.


On Thu, Jun 19, 2014 at 5:28 AM, Ken Kinman <kinman at hotmail.com> wrote:

> Hi all,
>
>       I'm glad Michael brought up the paper by Mitchell et al., 2013.
>  What he fails to mention is that the "Madagascar-New Zealand-subantarctic
> island" duck clade is only about 2.9 million years old (between a most
> likely minimum 1.78 mya and most likely maximum 3.95 mya).   How one could
> imagine stretching those dates back far enough for a vicariance event just
> makes me shake my head in disbelief.
>
>        The ratite dispersal was no doubt earlier, but still during the
> Cenozoic.  As for how Euphorbia seeds got from New Zealand to Madagascar or
> vice versa (or even from Antarctica in both directions), they probably
> stuck to the bodies of ducks or flying ratite ancestors or some other kind
> of bird.  Anyway, I am now even more convinced that dispersal was a major
> factor in ratite evolution.
>
>                                  --------------------------Ken
>
>
> -------------------------------------------------------------------------------------------------------------------
> > Date: Wed, 18 Jun 2014 16:40:29 +1200
> > From: m.j.heads at gmail.com
> > To: deepreef at bishopmuseum.org; taxacom at mailman.nhm.ku.edu
>
> > Subject: Re: [Taxacom] Dispersal paradigm (was: Antarctic dispersal)
> >
> > Hi Richard,
> >
> > You mentioned vicariance and dispersal in groups other than birds and
> > plants. Birds are used a lot in biogeography because they're the best
> known
> > group, but different groups of algae, fungi, insects, fishes (marine,
> > freshwater and diadromous), etc. are discussed in my Australasia book as
> > they illustrate standard patterns.
> >
> > You suggested that 'there are very, very few generalities we can make
> > concerning broad patterns in the history of evolution of life on Earth'.
> > One generality seems to be that the same distributions are, surprisingly,
> > repeated in groups with completely different ecology and means of
> > dispersal.
> >
> > For example, Ken brought up the Madagascar - New Zealand connection in
> > ratites (elephant birds and kiwis). The same distribution also occurs in
> > the beetle family Chaetosomatidae, and a correspondent has just written
> to
> > me citing a clade of ducks comprising four NZ species and A. bernieri in
> > Madagascar (Mitchell et al., 2013). In plants, Euphorbia glauca of NZ is
> > sister to E. emirnensis of Madagascar (Riina et al., 2013). These groups
> > all have very different ecology and means of dispersal, suggesting that
> > these factors are not the cause of the pattern.
> >
> >
> >
> >
>



-- 
Dunedin, New Zealand.

My recent books:

*Molecular panbiogeography of the tropics.* 2012. University of California
Press, Berkeley. www.ucpress.edu/book.php?isbn=9780520271968

*Biogeography of Australasia:  A molecular analysis*. 2014. Cambridge
University Press, Cambridge. www.cambridge.org/9781107041028