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Re: Molecular clocks and avian diversification

----- Original Message -----
From: "evelyn sobielski" <koreke77@yahoo.de>
Sent: Wednesday, October 25, 2006 12:35 AM

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.

Ah, thanks for pointing this out! The possible presence of a cartilaginous sternum in the Munich specimen nonwithstanding (that's the way I remember it anyways) -

It's the Berlin specimen. (It's amazing what people can overlook for 150 years. The Berlin specimen was recently shown to preserve a postorbital, too...)

as the example was hypothetical anyway,
simply replace the archies with "first bird w/sternum"
and "sternumless sister taxon".

The issue is that dromaeosaurs, troodontids (except *Jinfengopteryx*), and oviraptorosaurs all have ossified sterna. Therefore, no matter what their exact relationships, the lack of ossified sterna in *Archaeopteryx*, *Jinfengopteryx* and *Sapeornis* (assuming the absence in *S.* is real -- none of the specimens is fully articulated) is their own peculiarity (autapomorphy), and the presence of ossified sterna is the ancestral condition for the clade composed of birds and their closest relatives.