Re: Viva Neornithine Birds!

[john bois <jbois@verizon.net>]

Michael said:
>To have an impact, a mass extinction, and differential survival of neos and
enantis...and then say that the bolide cause of the latter is poorly
supported because we haven't worked out the differentiating mechanism is a
bit of a weak argument.

Fair enough.  But we don't know the order of those events.  The differential
survival may well have occurred _before_ the mass extinction.  With only one
bird species surviving we _cannot_ invoke pre-boundary
competition/predation.  With more--and all of them neornithines--this
possibility remains open.
Or...
The extinctions may have been less severe in areas that neornithines were
dominant.
In any case, the point I'm trying to make is that these bird finds open up
new hypotheses, the _weakest_ of which (in my view) is that only
neornithines could be lucky!

> > The tyranny of this
> >  bolide-explains-everything is weakened by increased survival and
especially,
> >  differential survival of similar species!

> But that depends on how similar they really are.  The
neornithine/enantiornithine problem is particularly tricky because we don't
really have any phylogenetic degrees of freedom.  With living taxa, we can
either predict risk based on similar phylogenetic position (works pretty
well most of the time) or we can remove the phylogenetic effects and look at
functional trends.  With the avian survival trends, we're trying to explain
the phylogenetic position effect in the first place, without really knowing
the functional signals.  How similar are they really?

Great question.  Wish I knew.  How similar were _non-avian_ dinosaurs to
each other?  Similar enough, apparently.  And what level of severity is
enough to spare neornithines and do in enantiornithines?
BTW, do you know of a reference that compares likely functionality of the
respective clades?