[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Viva Neornithine Birds!



David M. said:
> 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.

How is this relevant when what we are talking about is origin of _different_
clades before the boundary?

> 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. Remember: you need to find all possibilities because
> you can't test hypotheses that you've never thought of.

And yet many were content with the "shorebird" hypothesis and somewhat
insistent on its exclusivity (Livezey and Zusi criticize it rather strongly,
BTW).  In any case, "finding all possibilities" verges on obfuscation.
There are two primary sets of hypotheses.  One set is inspired by a glib
attraction to _luck_.  The other involves the attributes of different
species.  New data cull hypotheses.   The more clades of neornithine birds
whose divergence dates before the boundary, the less random are the
extinctions, i.e., we have to look for reasons: why neornithine and not
enantiornithine survival.  Do the data lead us to look harder at the
southern continents?  If so, are we talking about a pre-boundary dominance
of neornithines there; followed by significant survival due to less
intensive bolide effects (then why not nonavian dinosaurs as well)?

The rest of this post is self defense and not of general interest--assuming
the above is, that is.

David quoted Livezey and Zusi to show that my quote was over-selective:

> Here's the whole paragraph for context (refs removed):
>
> "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."
>
>
> As you can see, "this record" is not the fossil record,

I thought this was apparent from the quote I used: "despite the
vulnerability of such data
to suboptimal rooting..."  Sorry, if not.

> and Livezey and Zusi don't talk about their own data here, but about the
molecular data of others
> and their interpretation by others...

Given the list traffic about the phenomenal number of morphological
characters included in Livezey and Zusi's analysis, I assumed this also
would have been understood.  I probably shouldn't have.  I was not trying to
mislead...my intent was to use the authority of Livezey and Zusi to weigh in
heavily on the
molecular data--conclusiveness is so hard to come by (and I'm not saying we
are there yet).