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Still more Archaeopteryx
In reply to Shaun Sinclair"
Ah Shaun, you stepped right into it. What comes first? The structure or the
ability? Evolutionary biologists have argued this for ages. Logically, it is
a progression of steps with incremental changes until something truely
different/advantageous develops and takes off (pardon the pun). As Steven
Jay Gould points out, evolution may not be all that incremental, it may
stagnate for long periods of time interspersed with large leaps of
development. However, Archaeopteryx may well be a very good example of an
incremental development that may have lead to flight, or may not have.
I did not mention the hopping vs. running point to indicate that I thought
Archaeopteryx was a two-footed hopper, quite the contrary. Modern birds,
like crows, walk one foot at a time (left right left right), but
occasionally hop and flap to get to another location quickly or to at least
leave their location in a hurry. The lift required to do this comes from
having a keeled breast bone making for larger muscles powering the wings.
Therefore, as Archaeopteryx did not have a keeled breast bone, it likely
could not get into the air from a stationary stance on the ground. As others
have pointed out, birds that run a lot ie. roadrunners, keep their wings in
to avoid drag. They don't flap or glide to catch prey. So, it is at least
likely that Archaeopteryx did not do this either. There are similarities
between the clawed hands of Archaeopteryx and
<<All the gliding animals mentioned up to now (excepting avians) have
_failed_ to <<produce powered flight (flying squirrels, lemurs, etc.), so
how does gliding fit in to the <<evolution of powered flight?
The recent evidence points to theropods as being the ancestors of birds,
and, I believe, Archaeopteryx was a theropod (or very similar). It has
feathers, but not the other structures associated with modern birds (keeled
sternum and shoulder ligature) that enable them to develop lift and fly. So
what were the feathered arms and tail for? Probably gliding and weak
flapping. Perhaps, the distant offspring of Archaeopteryx were the only ones
to generate the right combination of mutations that enabled them to fly. It
isn't far fetched when you look at the evidence.
I don't buy the argument that because "flying" squirrels did not develop
flight from gliding then birds did not either. After all, bats fly quite
well, but not in the same way as birds or with the same wing structure that
birds have. There are different ways to get to the same end (Convergent
evolution). Unfortunately, we may just have to accept that Archaeopteryx had
feathers, didn't fly very strongly and may have glided better. Whether it
lauched itself from a tree or from the ground may be a moot point (and one
that is impossible to resolve until more specimens of feathered dinosaurs
Welcome to the discussion Shaun.
Toxic Chemicals Biologist by necessity,
By-stander and Observer of Paleontology by interest