Re: Molecular clocks and avian diversification

[Michael Mortimer <mickey_mortimer111@msn.com>]

evelyn sobielski wrote-

> Neornithine seabirds from the Maastrichtian ought to
> have been found if there was appreciable diversity.
> Landbirds, ditto. More material than Tytthostonyx,
> Polarornis, and other wretched stuff at least.

Why is Polarornis wretched?  I know it's described by Chatterjee, who has a 
bad record of correct identification, but it's a fairly complete specimen 
for a Mesozoic neornithine.

> Assuming A. bavarica was a distinct species and is
> correctly assigned to genus (i.e. representation of a
> distinct but adjoining or possibly barely overlapping
> gene pool), it might have given rise to a distinct
> clade of sternal-keel-muscled flyers, whereas A.
> lithographica could have resulted in a clade of
> coracoid- or whatnot-based flyers, all because of the
> small difference in thoracal skeleton.

The supposed sternum in the A. bavarica holotype turned out to be a coracoid 
(Wellnhofer and Tischlinger, 2004).  Archaeopterygids seemingly join 
Sapeornis and Jinfengopteryx as the only paravians lacking ossified sterna.

Mickey Mortimer