[Taxacom] Incongruent phylogeny and geology

[John Grehan]

Interesting points, although I was looking more for specificity with
respect to analyzed examples. It is certainly an interesting question of
how to apply fossils to a molecular phylogeny when the molecular
arrangement does not correspond with the morphological so that a fossil may
be directly integrated in the morphological analysis, but not the molecular
(for example with hominid evolution).

The trouble with dispersal abilities is that what one sees empirically is
the operation of dispersal as an ecological process of survival. The
problem of dispersal for analyzing the biogeography of differentiated
entities lies in translating that ecological means of survival into
conjectures about rare or extraordinary processes to account for vicariant
distributions.

True - just because something is purported to be old enough does not prove
that a particular geological event was involved. But if the biogeographic
structure did correspond to a tectonic feature associated or responsible
for that mountain building then one has biogeographic evidence to suggest
such a relationship.

John Grehan


On Thu, Apr 10, 2014 at 9:47 AM, David Campbell <pleuronaia at gmail.com>wrote:

> For whatever taxon you happen to be looking at it's necessary to check each
> of these.  What fossil record do we have?  Where did they occur in the
> past?  What changes occur over time?  How long ago were they present?  How
> do the fossils fit into the phylogeny?  For example, the first appearance
> of a representative of a stem group is not the date of the split between
> the two members of the crown group that happen to be in your molecular
> analysis (names omitted to protect the guilty).  How good is the fossil
> record?  Can you say anything at all about it?
>
> Dispersal abilities: Some organisms can readily survive a long float or
> swim, some can't.  Some can run, swim, fly, or hitchhike, some can't.  Real
> organisms are neither limitless dispersers nor completely passively
> vicariant, but fall somewhere in between.
>
> If you establish what a given organism likely could or couldn't cross, then
> you can carefully research current geological understanding to see what
> barriers and bridges may have been present at different times.
>
> But too often geology in biological papers is a handwaving "my dubiously
> calibrated molecular clock says 357.497 million years ago, and I think
> that's about when some continent collided, so I have proved that mountain
> building led to the origin of the clade."
>
>
> On Thu, Apr 10, 2014 at 6:41 AM, John Grehan <calabar.john at gmail.com>
> wrote:
>
> > David,
> >
> >
> >
> > Variability in timing from a particular geological event is definitely a
> > worthwhile consideration although specifics may be problematic where
> > assumptions are made when a taxon located either side of a previous
> > 'barrier' is assumed to have crossed that barrier. The veracity of such
> > arguments would have to be assessed case by case. There are taxa north
> and
> > south of Panama that may have already occupied land to the north and
> south,
> > there are taxa that may have originated from the Panama terranes out of
> the
> > Pacific, and there are taxa to the north and south that never occupied or
> > 'crossed' the Panama isthmus.
> >
> >
> >
> > With Wallace's line (as example of a boundary that is often represented
> as
> > a dispersal barrier) assumptions are often made that a taxon on one or
> > other side is a demonstration of that taxon having been restricted by
> > Wallace's line acting as a barrier, and yet on the other side there may
> be
> > a sister taxon which would show that the 'line' did not function in this
> > way at all.
> >
> >
> >
> > I would be interested to know in more detail as to what you mean by
> > careful examination of the fossil record, dispersal abilities, and
> detailed
> > geological analysis for correlating a particular point on a tree with the
> > event in question. Perhaps you could give an example.
> >
> >
> >
> > John Grehan
> >
> >
> > On Wed, Apr 9, 2014 at 4:35 PM, David Campbell <pleuronaia at gmail.com
> >wrote:
> >
> >> Geological evidence is often relatively coarse-scale, and neontologists'
> >> ideas of geology often much vaguer still.  In the real world,
> connections
> >> and gaps between continents or ocean basins do not abruptly jump from
> >> impassible to easily traveled and vice versa; different species have
> >> different dispersal ability and are stopped or not by different
> barriers.
> >> Thus, an event such as the closing of Panama does not have a magic fixed
> >> date at which every land and freshwater species crossed and every marine
> >> species stopped crossing.  Land mammals (probably decent swimmers) began
> >> to
> >> cross by about 10 million years ago, but the trickle became a flood
> about
> >> 2.5 million.  The southernmost part of the isthmus geologically is
> >> geographically northwestern Colombia, and probably was in place about 10
> >> million years ago, but shallow marine connections persisted as recently
> as
> >> 2.5 million.
> >>
> >> These issues are quite commonly a problem in molecular clock
> calculations.
> >> Calibrations based on tectonic events rarely involve careful examination
> >> of
> >> the fossil record, dispersal abilities, and detailed geological analysis
> >> that would be necessary to actually correlate a particular point on the
> >> tree with the event in question.  Likewise, when dates are calculated,
> >> many
> >> different things are happening geologically at any given time, and
> honest
> >> error bars for molecular clocks are quite wide, so the range of possibly
> >> correlating events is in fact very wide.
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> >>
> >> Celebrating 27 years of Taxacom in 2014.
> >>
> >
> >
>
>
> --
> Dr. David Campbell
> Assistant Professor, Geology
> Department of Natural Sciences
> Box 7270
> Gardner-Webb University
> Boiling Springs NC 28017
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>
> Celebrating 27 years of Taxacom in 2014.
>