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Re: Molecular clocks and avian diversification
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.