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RE: VARIABLE OSSIFICATIONS



 I was clearing out my over-stuffed mailbox when I came across this little
tidbit from Darren Naish:


You may be interested to hear that furcular ossification sometimes 
never happens in some extant volant birds - budgies and at least some 
owls for example - even though they have well developed cartilaginous 
furculae. I am not aware of bird species where furcular ossification 
pends on individual variation BUT in one of the Hawaiian moa-nalos, 
_Thambetochen_, one population has an ossified furcula, while another 
population does not (Olson and James 1985). This is based on a small 
sample size, but Bradley Livezey does cite it as reliable in one of 
his anseriform relationships papers.

What is the ref. for the presence of cartilaginous furculae in budgies and
some owls, Darren? I am a little puzzled because I had always thought that
the clavicle was a dermal element and as such should not be preformed in
cartilage. Are bird furculae not homologous with clavicles after all? Or can
a bone that is historically dermal, switch to being endochondral during
evolution? I hope someone has the answers.

cheers

Adam Yates