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Re: Viva Neornithine Birds!
> "Quantitative estimation of rates of evolutionary
> change [...] -- given
> robust phylogenies [...] and adequate fossil records
> [...] -- have fostered
> more detailed hypotheses of phylogenetic bottlenecks
> and 'explosive'
> radiation near the K-T boundary [...]. However,
> there is growing evidence,
> at least based on Bayesian analyses of data largely
> or entirely from the
> mitochondrial genome, that most or all neornithine
> orders date from the late
> [sic!] Cretaceous [...]. If accurate, despite the
> vulnerability of such data
> to suboptimal rooting, this record undermines early
> anticipations of K-T
> boundary effects in modern orders and an
> evolutionary timespan in which
> major divergences of neornithine lineages would
> extend through the early and
> middle Cenozoic. Expectations for avian fossils of
> such antiquity are
> correspondingly conservative, and although fossils
> of such age potentially
> offer new calibration points for early avian
> lineages, there is diminished
> hope for points of calibration bearing on the
> relative antiquity of modern
> (super)orders of birds or precise molecular
> estimates of associated
> evolutionary rates characteristic of phylogenetic
> lineages."
Would one not expect even (or especially?) in a
reasonably well-calibrated model the "molecular"
divergences (which starts with cessation of
significant gene flow between sister populations, i.e.
more often than not at the species level) to predate
the fossil one (which is based on distinct osteology,
which only can start some time *after* lineages *have
separated*)?
For example, let's assume that that Psittaciformes and
Columbiformes are sister lineages, which seems fairly
reasonable. If 2 populations of what was then e.g.
distinct genera, which, were they known from fossils,
would nowadays be placed in the stem and close to each
other* in the "near passerine" assemblage, survived
the Big One somewhere in the general vicinity of
Australia - would that not produce the pattern the
different analyses point to, i.e. molecular trees
indicate divergence some 65-70 mya, whereas trees
based on the fossil record indicate marked
osteological differentiation starting some 60-65 mya?
(I chose the two groups because of their biogeography
and phylogeny, not because they actually show this
phenomenon in cladistic analyses basd on fossils -
their Paleogene fossil record is very insufficient).
> > Well, I hope not, because this would mean
> neornithines were special.
>
> If one breeding pair -- or even just a female
> capable of parthenogenesis, in
> the case of Neornithes at least -- survives a mass
> extinction, all clades it
> belongs to have survived. This is different from the
> hypothesis that the
> mass extinction didn't affect those clades at all,
> and yet again different
> from the hypothesis that the mass extinction
> consisted of said clades
> outcompeting others.
Bluntly: no need to be special, you just need to be
lucky.
Given that the fossil record points at an out-of
Australia (or adjacent Antarctica) for Cenozoic
radiation of at least Palaeognathae, Anseriformes,
Psittaciformes, Columbiformes, Passeriformes, and
probably (Antarctica) Galliformes (and these are just
the clades which come to my mind spontaneously),
coupled with an apparently rapid expansion and
adaptive radiation via the opening Indian Ocean to
Africa, continental Eurasia via the Wallacea, and then
to NAm, and via Antarctica (and Africa?) to SAm, it
appears to me that what would need to be looked into
is the Late Cretaceous fossil record for
non-Neornithes from Australia or adjacent Antarctica
(which is IIRC all but non-existent).
The radiation models for the Cypselomorphae seem to be
a case in point: initial divergence appears to have
taken place generally speaking in the southern
Wallacean and/or Australian region if one looks at the
distribution of lineages. However, especially the
Apodiformes radiation apparently took place in the
latter half of the Paleogene, in Eurasia in all
likelihood (has anyone checked out the new
Eurotrochilus paper in J. Ornithol.?)
To sum it up, IMHO a snapshot of non-Galloanseres
neognaths at the K/P event would have revealed only a
few handfuls of family-level clades (excluding
non-survivor "waifs and strays", i.e. lineages which
stayed species-poor throughout their time of
existence) in maybe 5 order-level clades**; adaptation
and drift *in the Paleogene* produced the present-day
diversity *from already genetically distinct*
lineages.
Regards,
Eike
* That is to say, in the same family-level clade in
all probability, more likely than not even in the same
subfamily-level clade.
** In Linnean terms, a Charadriiformes order with
maybe 3-5 major lower-level clades, a "higher
waterbird" order which might (more probable methinks)
or might not have included the seabirds with (very
roughly) short of 10 families, and one or two (or
three?) "higher landbird" orders with between 2 and 10
families each, one of which would have included
"proto-Passeriformes" (which 65 mya were probably not
a distinct entity at higher than tribe level) - all
very crude estimates, and discounting minor ,
independent lineages (can't think of any surviving
ones really though that would have been distinct at
order level then. Perhaps buttonquails, if they are
not Charadriiformes but "intermediate" between these
and "higher waterbirds". But these are also centered
on the Wallacea-Indian Ocean region today).
Most all evidence indicates that Charadriiformes at
least were a) well distinct, b) fairly vigorously
radiating, and c) globally distributed 65 mya far more
likely than not. But again, the basalmost lineages in
any modern Charadriiform higher-level clade (i.e.
family- and tribe-level) are concentrated in the S
hemisphere, centered on the Australian region.
And then this: though it proves nothing, it is very
interesting to take a globe model of K/P earth and
mentally run a needle from Chixculub through the exact
center. Where does it emerge again?
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