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Re: No Cretaceous placental mammals?
> > E.g. the case for survivorship of maybe a dozen
> > Charadriiformes lineages is reasonable.
> Why? There's no analysis with a large number of
> calibration points with
> upper bounds that argues for this, right?
Yeah, that's why I said "reasonable" - one can reason
for and against it but it's not just a shiny idea;
there's quite some data (little fossil, unfortunately)
which every serious model must not contradict, and
there is at least no material evidence that
*precludes* it. Compare for example the proposed
Santonian basal divergence of crown parrot lineages,
which requires that parrot autapomorphies (beak,
skull, foot, ...) either are a more extreme example of
homoplasy than even foot-propelled divers' hindlimbs
(if the pseudasturids are Psittaciformes), or that
they evolved *before* the Santonian (if the
pseudasturids are not psittaciform), or that we have a
case of character reversal that is simply stunning (if
the "parrot autapomorphies" are actually
Psittaciformes plesiomorphies so that the
pseudasturids can still be Psittaciformes after all,
autapomorphic in their own non-parrot way as they
were). Fat chance either way.
I try asking "how well does the proposed model fit the
available *material evidence, all of it*?". If the
answer is not "100% or pretty damn close to it", the
model needs to be corrected. Then only I ask, "how
complete is the material evidence?". Fossils are
material evidence. Raw DNA sequences are material
evidence. Controversial assignments of fossil material
to crown lineages and uncalibrated molecular clocks
are a far cry from being material evidence.
In crown Aves, the problems are much more often with
question 2 than with question 1 by now.
I'd like to see - or if, some day, I have the time and
resources and reputation and whatnot, and nobody did
it til then, I'll do it myself - all the isolated
humeri, tarsometatarsi, ... scored and evaluated using
only that single bone from a wide range of taxa living
and prehistoric, and with a matrix that is so
fine-grained that the foot-propelled divers *won't*
cluster. Milk a single element for all the
phylogenetic signal that it holds. Might be that this
is a reasonable way to crack the afiliations of the
assorted crumbs we have laying around from the New
Jersey marls etc; I don't think it has been tried yet
(not for these bird fossils at least).
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