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FEVA (Flight Evolved Via Aerobics!)

Okay, this is one of those 3 A.M., made-sense-at-the-time, type ideas, so
bear with me.

We've had the flight stroke explained as a predatory strike, a swimming
movement and lots more besides. But what nobody has been mad enough yet to
suggest is that it was a requirement of the theropod respiratory system.

The main thing all (more or less!) theropods and birds have in common is the
furcula. According to Jenkins, Dial and Goslow, 1988 the furcula forms an
integral part of the avian respiratory system. Very simply put, flapping the
arms alters the shape of the furcula, and the rest of the thorax, then it
springs back at virtually no metabolic cost. This acts as a pump to force
air through the birds' fairly rigid lungs and air sac system. It provides a
cheap and easy way of aerobically fuelling high-cost activities, and offers
temperature control benefits. This is a serious metabolic edge during
strenuous activity, but it only works if you flap.
So, try to imagine a Coelophysis, running after prey. Flat out, short on
breath and overheating, it flaps it's arms, so getting mechanical help with
breathing and heat loss, and catches it's dinner!
Thus we have a flight stroke, used not just once for predation, but as a
regular part of high speed running.
Jump forward in the Mesozoic, to a time when a small
Microraptor/Sinornithosaurus-type creature is clambering about in the trees.
It's arms have lengthened for climbing, and they are covered with feathers
(brooding/ insulation/ display/ basal to Archosauria/ whatever). Threatened
by a predator, it scampers higher, branch to branch. Desperate to escape, it
leaps to the next tree. To meet it's aerobic requirements, like it's
ancestors before it, it flaps it's long, feathered arms and hey Presto! it's
a bird.

Okay, I know it makes a lot of assumptions (air sacs in basal theropods, for
one.) Feel free to criticise in the harshest manner possible.....
Michael Lovejoy