This time I don't especially agree
with Ian Fraser's avian whimsy in GG. Although it is interesting as are
most. I am not convinced that the alula is anything to consider as
unusual or even particularly notable. Sadly Ian suggests the alula is
at the "elbow" although he does get around to correcting that. It
certainly isn't there. The shoulders, elbows, wrists and fingers of
birds are all features easily observed from any plucked chicken,
whether cooked or not. They are in the same position as in humans. It
is well worth considering this arrangement for a really big long-winged
bird like an albatross as to how the wing is folded down. When an
albatross folds its wings, its elbow sits over its rump.
The alula is the group of feathers
attached to the second finger. So it is not the elbow, if anything it
could be called near the wrist. As the third and fourth fingers of the
hand hold the primary feathers, it is hardly surprising that the second
finger (which looks more like the thumb) should also have feathers
attached to it. Indeed it would be odd if they didn't. As for the
development of these feathers, this is not that odd or difficult to
understand. Within the last few hundred years, domesticated forms of
both pigeons and chickens have been bred that have feathers on their
toes. This is more remarkable than that the second finger should have
feathers attached to it. I don't know much about the aerodynamic
features of the alula, presumably they do help. I note though that
all bats fly well, without any convergent feature. The reason that
Archaeopteryx did not have this feature presumably relates to that it
still used its fingers with claws on, for climbing.
Philip
No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.5.488 / Virus Database: 269.14.6/1059 - Release Date: 9/10/2007 8:44 AM
