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Re: Molecular clocks and avian diversification



> 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.

"Chatterjee (2002) reported another supposed loon,
Polarornis gregorii, from the Cretaceous of
Antarctica, of which were found the proximal part of
the bill and the adjacent distal part of the cranium,
parts of the otic region, four vertebrae, a small
sternum fragment, a femur, and a proximal tibiotarsus.
Despite this very fragmentary preservation, Chatterjee
(2002) presented a detailed
‘‘reconstruction’’ of the
entire skeleton and a complete skull in which most
parts were ‘‘constructed by pressing (...)
paper pulp into a mold that was sculpted first in
clay’’ (Chatterjee 2002, pp. 128); it is
difficult to understand why Chatterjee (1997, pp. 117)
described the skull of Polarornis as being
‘‘fairly intact, beautifully
preserved’’ and figured a drawing of a
complete skull with no indication that substantial
parts were reconstructed and are not preserved in the
specimen." (Mayr, J. Ornithol. 145: 281).

It might be fairly complete, but wretched things have
been done to it ;-)

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

Eike


                
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