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Feathers vs. tryosseus cannal
Hi, girls and boys! Somebody (I'm sorry, I always forget the names) asked about
when appeared the tryosseous cannal in birds. Well, it's difficult to answer e
xactly, because no articulated pectoral girdle is known from Lower Cretaceous b
irds. But the displacement of the articulation area between the coracoid and th
e scapula from the proximal end of the coracoid towards a more distal zone appe
ars in _Iberomesornis_. So, a structure similar to the tryosseus cannal is pres
ent in such an ancient bird. The supracoracoideus muscle has changed its functi
on in this tiny bird.
The most ancient feathered theropod known is _Archaeopteryx_, which is about 20
-30 m.y. older than _Iberomesornis_, and also more primitive. So, the feathers
appeared before than the tryosseous cannal. Following your three theories, the
feathers appeared for some function (insulation, maybe?) different from the fli
ght. And then, some of them, the feathers of the wings and tail, exapted (no co
-opted) to other function, the flight.
There is other problem. Why you suposse that the birds without a tryosseus cann
al couldn't flight actively? Ok, they couldn't flight as well as those whose ha
ve it, but probably they could flight well enough to move around.
I think that's all, folks! Nino.