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Re: Molecular clocks and avian diversification
----- Original Message -----
From: "evelyn sobielski" <email@example.com>
Sent: Tuesday, October 24, 2006 11:18 PM
> A nice way of putting what a biomedical researcher
> seeking major founding would without doubt have
> called "...will revolutionize our understanding of..."
Where's the revolution?
Molecular dating finally being based on sound science.
birds are quite state-of-the-art in the matter; other
branches of evo-bio are not really arrived at relaxed
I hope you're kidding... :-S Are you saying fixed clocks are still used
An Early Cretaceous date for the basal
divergence of Neornithes is highly suspect. And so
Not necessarily as deep as suggested, true. But
possible (though not really likely).
Judging from the Yixian Fm... is it possible that they were all hiding in
What's so "very distinct" about it?
Vegavis was a full-fledged member of a crown-group
family (which later became extinct due to other
OK, but this doesn't require a great distance in time from the origin of
So you think there was a trichotomous split?!?
Not really, I think that trichotomous vs dichotomous
is a matter of perspective. Evolutionary lineages do
not necessarily have a thickness of 1 as cladograms
What do you mean?
The Galliformes are particularly interesting: anything
with a gamefowl lifestyle seems to be so much prey in
the Late Cretaceous ecosystem. There were terrestrial
theropod predators, airborne enantiornithine predators
That's no worse than today, IMHO.
They were not a monophyletic group. And "graculavid"
(as form taxon) birds do not come just form NJ, only
the ones that were placed in the presumed "family"
were (or at least from the general area). Vegavis
would have been placed in the Graculavide (Presbyornis
Oh, that's what you mean. But if it's _so_ broad, "Graculavidae" is useless
even as a form taxon.
Paleogene radiation suggests a Late Cretaceous split
as more likely.
Or a split in the ecological vacuum of the early Danian...
Neornithine seabirds from the Maastrichtian ought to
have been found if there was appreciable diversity.
Not necessarily. The Maastrichtian fossil record of badly preservable
terrestrial animals is pretty bad.
Don't confuse cladogenesis ( = any halfway permanent
split of a population
in two) and speciation. Those aren't the same...
except under some species concepts...
I don't, but speciation is necessary for cladogenesis.
Then you are confusing them. :-) Speciation _as understood by the Biological
Species Concept_ is necessary for _irreversible_ cladogenesis, but I'm not
restricting myself to that. Browse the archives, and you'll find lists of
fertile hybrids between extant "genera" -- clearly unreversed cladogenesis
has occurred without being irrevers_ible_.
Any lineage should have passed through a point where
it was a lower-level taxon in the Linnean system, e.g.
a genus or species.
The Linnean system only serves to confuse such issues. It's a smokescreen.
Hmmm... a drawing of the evolutionary relationships of
these ducks would help. The result is something that
cannot be represented by a dichotomous tree, not if
you permit trichotomy either. A result that cannot
come from a cladistic analysis, hence: cladistics does
not help in this case.
Strictly speaking that's true, but the fact that introgression will be shown
as systematic convergence on a cladogram should certainly help in
recognizing possible introgression. Only clade origins by hybridization or
outright lineage fusion (shown in the figure of
http://www.ohiou.edu/phylocode/art1-3.html) will really throw cladistics off
track -- the cladogram will then contain a trichotomy.
This is not cladogenesis, granted - but it is a case
for what may happen at nodes because (without further
research) all active speciation events are possible
nodes in a phylogeny.
I don't understand "active speciation event".
Or: what were the first-diverged (as opposed to
last-common) ancestors of 2 sister clades? Certainly
living, breathing animals. Sister species? Usually.
Not even necessarily different species. They could have been populations of
the same species -- depending on the species concept. (For example, the
Hennigian species concept takes cladogenesis and calls it "speciation";
under that concept those ancestors automatically belong to different
(That's what I
meant in the "trichotomy" bit on Galloanseres above:
gamfowl and waterfowl are apparently early
Oh. So just two dichotomies separated by a short internal branch?