[Taxacom] Antarctic dispersal (was: Another blow to vicariance in ratite evolution

[John Grehan]

Ken,

The point about the division is that if one is going to invoke extensive
dispersal then one has to explain how that dispersal happened in just such
a way that it did not eliminate the allopatry between the Indian Ocean
clade and the northern clade. Vicariance does not raise that contradiction,
and a vicariance origin of the two clades does address the evolution and
biogeography of the southern clade as having originated over its current
range from a widespread ancestor with a range that also included the
northern group. Nothing complicated about that.

It's a bit perplexing to understand the fossil calibration 'excuse' to push
back the time scale. The fact is that fossils and fossil calibrations are
only minimal dates. To project them as anything but is to invoke a kind of
mysticism for scientific method. While one may (or may not, I presume you
have not done a survey) be hard pressed to find any (actually Mike is a
botanist so your assertion is thereby falsified) who believes
Crossosmatales as a whole is older 110 million years, but a majority
opinion of itself does is not a necessary correlate of actuality. One would
have been hard pressed to find many biogeographers who accepted continental
drift back in the 1950's, but that did not mean they were correct in their
belief.

On what analytic basis is dispersal to Madagascar a "fairly safe bet"?

Antarctica was naturally an important element in Southern Hemisphere
biogeography, although perhaps less as a highway than as being associated
with different centers of differentiation as highlighted in Heads' book (a
section that should interest you very much).

Cheers,


John Grehan




On Mon, Jun 9, 2014 at 12:40 PM, Ken Kinman <kinman at hotmail.com> wrote:

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> Hi Michael,       I wasn't discussing the division of Crossosomatales into
> two main clades (southern and northern).  That might have been by
> vicariance or maybe not.  What I was discussing, and which you did not
> address in your comments, was the subsequent evolution and biogeography of
> the southern clade.  That is a more complicated issue which simple
> vicariance cannot readily explain---unless of course, one once again uses
> the fossil calibration excuse to push back the time scale tens of millions
> of years earlier.  Funny how that excuse comes up so often in these
> discussions.
>        In any case, the maximal ages of eudicot orders are fairly well
> constrained because the pollen record is so good (far better than the
> macrofossil record).  You would be hard pressed to find any botanist who
> believes Crossosomatales as a whole is older than 110 million years (and
> 125 million years is the accepted age of the entire eudicot clade).
>  Dispersal to Madagascar (and from there to the Seychelles and Mascarene
> Islands) looks like a fairly safe bet. What's so complicated about that?
>      And I certainly wasn't arguing in favor of "everything was
> everywhere".  However, Antarctica formerly played an important role in so
> many taxa as they dispersed through or from that continent  As more fossils
> are discovered in Antarctica, it will no doubt show that evolution is often
> more complicated than we once thought, and molecular evidence already has
> (ratite phylogeny certainly seems to be).  Invoking too much "simple"
> vicariance seems overly simplistic to me.
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> Date: Mon, 9 Jun 2014 16:45:32 +1200
> Subject: Re: Antarctic dispersal (was: Another blow to vicariance in
> ratite evolution
> From: m.j.heads at gmail.com
> To: kinman at hotmail.com; Taxacom at mailman.nhm.ku.edu
>
> Hi Ken, The Indian Ocean clade of Crossosomatales (Madagascar - New
> Zealand and vicinity) has its sister group neatly allopatric to its north
> (New Guinea, Sri Lanka etc. northwards), so the simplest explanation is
> that they both originated by vicariance. The break between the two (located
> between Madagascar and Sri Lanka, between New Caledonia and New Guinea,
> etc.) coincides with belts of major rifting as well as breaks in countless
> other groups.
>  The 80 m.y. date for the clades is fossil calibrated and so it is a
> mimimum age. This is useful as it rules out earlier events (not older ones)
> as possible causes.   For the ratite clade, you seem to be supporting the
> idea that everything was everywhere and then gradually the distributions
> formed by extinction. So how and why were they everywhere to start with? It
> just gets more and more complicated for a very simple case of allopatry.
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> On Mon, Jun 9, 2014 at 2:55 PM, Ken Kinman <kinman at hotmail.com> wrote:
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> Hi Mike,
>         The Crossosomatales southern clade is probably only about 80
> million years old, so dispersal to Madagascar seems to be a good bet (and I
> believe it also dispersed to the Seychelles and Mascarene islands as well).
>  This clade probably existed in Antarctica and Australia (fossil pollen
> records), so the current distribution is no doubt a combination of early
> vicariance, later dispersals, and then extinction in intervening areas
> (including Antarctica and Australia).  I don't know much about the beetle
> family Chaetosomatidae, but perhaps Stephen Thorpe might have an opinion on
> that.
>
>          In any case, since only that beetle family has the same
> distribution as the elephant bird-kiwi clade, I would certainly not call
> that much of a pattern!!!  And the elephant bird-kiwi clade is probably
> even younger than 80 million years old, so dispersal of a flighted ancestor
> (of kiwi and elephant birds) from Antarctica in the early Cenozoic seems a
> very probable hypothesis, and again followed by extinction of the clade in
> Australia (due to competition with other ratites) as well as extinction in
> mainland Africa (due to competition with early ostriches).
>
>         So if there is a pattern to be seen in such cases, I would suggest
> that Antarctica is going to be a major factor, and that the massive
> extinction of the biota in Antarctica during the early-to-mid Cenozoic (and
> paucity of a known fossil record there) makes vicariance more appealing
> than it actually is for many taxa.  In particular, the multiple losses of
> flight among ratite taxa makes perfect sense to me.  Why John calls such
> suggestions ignorant (much less stupid) baffles me.
>                          ----------------------------Ken Kinman
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> Date: Mon, 9 Jun 2014 11:12:39 +1200
> Subject: Re: [Taxacom] Another blow to vicariance in ratite evolution
> From: m.j.heads at gmail.com
> To: kinman at hotmail.com; taxacom at mailman.nhm.ku.edu
>
>
> Hi Ken, On p. 74 of my 2014 book I cited the beetle family
> Chaetosomatidae, known only from Madagascar (Malgassochaetus) and New
> Zealand (Chaetosoma, Chaetosomodes). A similar pattern in plants occurs in
> the southern hemisphere clade of Crossosomatales; it's in Madagascar (also
> the adjacent coast of Africa and Cape Town) (Aphloia, Geissoloma) , New
> Zealand (Ixerba) and New Caledonia (Strasburgeria). (Both examples are
> cited, with references, in my 2014 book, p. 74).
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