Still more Archaeopteryx

["Constable,Miles [Edm]" <ConstableM@mail.edm.ab.doe.ca>]

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 
are found.

Welcome to the discussion Shaun.

Miles Constable
Toxic Chemicals Biologist by necessity,
By-stander and Observer of Paleontology by interest
Constablem@edm.ab.doe.ca