W
Walter Dnes
Guest
I posted a half-formed theory to this group years ago,
regarding the evolution of flight in birds. Here it is
again, this time with a lot more detail, and a lot of loose
ends cleaned up. The following is a an almost verbatim text
dump from an essay I've posted on my home page.
>From Sea to Sky, the Ascent of Birds
====================================
There have been many theories about the origin of aerial
flight in birds; here's mine. Since Archeopteryx is
generally recognized as the earliest bird fossil, it's a
convenient place to start. There has been much speculation
about how, and for that matter, if, it managed to fly.
Let's look at what we do know...
* Archeopteryx did not have the weight-saving
adaptations of modern
* birds,
i.e...
+ it had not lost its teeth
+ it did not have the lightweight bones of modern
birds
+ it had a real tail which, besides adding extra
weight and drag, moved its centre-of-gravity well
behind its wings
* the wingtips did not have long primary flight feathers.
* that point was moot, because the shoulder joint did not
allow the wings to be raised much above horizontal
* that point was moot, because there was no hole through
the shoulder joint through which to pass the large
tendon that gives the rapid and powerful wing upstroke
in living birds
* and that point was also moot, because it lacked the
prominent breastbone of modern birds, onto which to
attach large muscles to contract those tendons.
To summarize...
1. It was too heavy to be a glider. Gliding also implies
climbing up some structure in order to be able to jump
off it. The desparate attempts to picture a "bird"
clawing it's way up a tree are laughable. That fact that
the paleo-climate of the Solnhofen Lagoon district
during Archeopteryx's time was desert-like, with no
large trees in the vicinity, should help kill that idea.
2. As for powered (i.e. flapping) flight, it didn't have
the breastbone to which to attach muscles to contract
the tendons it didn't have, which didn't pass through
the holes that it didn't have in its shoulders, which
didn't have the joints to allow flapping of its wings,
which didn't have long primary flight feathers.
3. And in any case, the claws on the leading edge of its
wings would destroy the aerodynamic airflow, and the
long bony tail would push the centre-of-gravity well
back of the wings.
Archeopteryx never flew; deal with it.
Could Archeopteryx be a flightless descendant of a bird
that flew? Since Archeopteryx is the earliest known
feathered and winged fossil, that seems rather unlikely.
That idea would also require totally insane reverse-
evolution, i.e. the shoulder joint reverting to theropod
style, and the return of teeth. So we can safely
conclude that none of Archeopteryx's immediate ancestors
flew, either.
Well, if none of Archeopteryx's immediate ancestors flew,
that implies that it evolved aerodynamic feathers (picky,
picky, picky) and wings for reasons other than aerial
flight (picky, picky, picky). Any theory of the evolution
of aerial flight in birds must address that issue. It
would also be nice to be able to explain how the first
attempts at flight could result in crash-landings without
killing the bird, or maiming it to the point where it was
unable to fend for itself, and starved to death, if it
wasn't eaten by a predator.
My theory starts off with a feather-covered theropod that
is ancestral to Archeopteryx. For anybody who doesn't like
that idea, I refer you to Sinosauropteryx, Caudipteryx,
Shuvuuia, Sinornithosaurus, Beipiaosaurus, etc. Here is
how I propose things went...
4. We start off with pre-Archeopteryx, a small, bipedal
theropod with forelimbs like those of Coeleurosaur. It
has an insulating coat of feathers.
5. Pre-Archeopteryx discovers that plants, crustaceans, and
even the occasional fish along the shore are delicious.
This discovery may have been accelerated by climate
change which reduces food supply away from the shore. In
pursuit of its food, it starts spending more and more
time in the water.
6. What happens to land-dwelling vertebrates that start
spending a lot of time in water? Riiiiiiiight! Their
limbs tend to evolve into flippers. Our feathered,
bipedal, theropod's forelimbs start looking like wings.
Part way through the process, it will still have some
claws on the leading edge of the flippers. Since it
still spends some significant time on land, it's feet
will still be that of a land animal. It's a bird, it's a
plane, no it's our friend Archeopteryx.
Things start making sense now. The reason that we find
Archeopteryx's fossils only in a lagoon, is because it
was a flightless feathered theropod that spent quite a
bit of time in water. A flightless bird/theropod that
spends a lot of time in water doesn't have to worry
about shedding teeth to reduce weight. Claws on its
wings can be used to grab fish or other prey. The fact
that its feathers aren't suited for flight is moot.
Their purpose is to keep the animal warm, and not get
in the way when it runs around in the water. What
little swimming it does probably consists of breast-
stroke or dog-paddle, because it doesn't have bird-type
shoulder joints.
7. A few million years pass. After spending even more time
in water, adaptations continue. The feet get webbed and
the shoulder joints evolve to a bird-like mode to allow
raising its forelimbs above its shoulders. This allows a
more powerful underwater swimming stroke; actually
"flying underwater". To supply the necessary power, it
needs stronger muscles, and a place to attach them to
(keelbone). Now that it's wings are used for "flying
underwater", "flight feathers" start to be an advantage.
Since it hasn't yet flown aerially, there is no
advantage to shedding its teeth. Hesperornis would be a
reasonable specimen of this stage. Our flightless bird
spends a lot of time "flying underwater". It learns to
navigate in 3 dimensions, which will be important later.
The Avian Kitty Hawk
--------------------
A Hesperornis-like "flightless" bird is minding its own
business one day when along comes a big fish, or whatever,
that thinks of our bird friend as a yummy meal. It gives
chase and the bird flees, with rapid frantic wing-strokes.
Since it's an air-breathing animal, it needs to surface to
breathe. It's moving as fast as it can to escape its
predator, so that it not only gets to the surface, but
most of its body gets clear out of the water. Since it's
being pursued, it keeps flapping its wings... and flies
several metres before landing back in the water, giving
itself enough of an advantage to get to shore safely.
Having discovered flight and its survival value, water-
birds were able to able to parlay their "underwater-
flying" skills to aerial flight. Crash-landing in the
water after getting one or two metres into the air is a
lot less likely to kill/maim a bird than crash-landing on
hard land. Landing on floating logs, and then on branches
of floating logs will be the next step in acquiring tree-
landing skills, without killing themselves if they don't
do it exactly right the first time.
Birds didn't evolve aerodynamic feathers for the purpose
of aerial flight, they evolved hydrodynamic feathers for
the purpose of underwater flight; yeah, picky, picky,
picky. Yes, I have read Elaine Morgan's book "Descent of
Woman". Read into that what you will.
--
Walter Dnes; my email address is *ALMOST* like
[email protected] Delete the "z" to get my real
address. If that gets blocked, follow the instructions at
the end of the 550 message.
regarding the evolution of flight in birds. Here it is
again, this time with a lot more detail, and a lot of loose
ends cleaned up. The following is a an almost verbatim text
dump from an essay I've posted on my home page.
>From Sea to Sky, the Ascent of Birds
====================================
There have been many theories about the origin of aerial
flight in birds; here's mine. Since Archeopteryx is
generally recognized as the earliest bird fossil, it's a
convenient place to start. There has been much speculation
about how, and for that matter, if, it managed to fly.
Let's look at what we do know...
* Archeopteryx did not have the weight-saving
adaptations of modern
* birds,
i.e...
+ it had not lost its teeth
+ it did not have the lightweight bones of modern
birds
+ it had a real tail which, besides adding extra
weight and drag, moved its centre-of-gravity well
behind its wings
* the wingtips did not have long primary flight feathers.
* that point was moot, because the shoulder joint did not
allow the wings to be raised much above horizontal
* that point was moot, because there was no hole through
the shoulder joint through which to pass the large
tendon that gives the rapid and powerful wing upstroke
in living birds
* and that point was also moot, because it lacked the
prominent breastbone of modern birds, onto which to
attach large muscles to contract those tendons.
To summarize...
1. It was too heavy to be a glider. Gliding also implies
climbing up some structure in order to be able to jump
off it. The desparate attempts to picture a "bird"
clawing it's way up a tree are laughable. That fact that
the paleo-climate of the Solnhofen Lagoon district
during Archeopteryx's time was desert-like, with no
large trees in the vicinity, should help kill that idea.
2. As for powered (i.e. flapping) flight, it didn't have
the breastbone to which to attach muscles to contract
the tendons it didn't have, which didn't pass through
the holes that it didn't have in its shoulders, which
didn't have the joints to allow flapping of its wings,
which didn't have long primary flight feathers.
3. And in any case, the claws on the leading edge of its
wings would destroy the aerodynamic airflow, and the
long bony tail would push the centre-of-gravity well
back of the wings.
Archeopteryx never flew; deal with it.
Could Archeopteryx be a flightless descendant of a bird
that flew? Since Archeopteryx is the earliest known
feathered and winged fossil, that seems rather unlikely.
That idea would also require totally insane reverse-
evolution, i.e. the shoulder joint reverting to theropod
style, and the return of teeth. So we can safely
conclude that none of Archeopteryx's immediate ancestors
flew, either.
Well, if none of Archeopteryx's immediate ancestors flew,
that implies that it evolved aerodynamic feathers (picky,
picky, picky) and wings for reasons other than aerial
flight (picky, picky, picky). Any theory of the evolution
of aerial flight in birds must address that issue. It
would also be nice to be able to explain how the first
attempts at flight could result in crash-landings without
killing the bird, or maiming it to the point where it was
unable to fend for itself, and starved to death, if it
wasn't eaten by a predator.
My theory starts off with a feather-covered theropod that
is ancestral to Archeopteryx. For anybody who doesn't like
that idea, I refer you to Sinosauropteryx, Caudipteryx,
Shuvuuia, Sinornithosaurus, Beipiaosaurus, etc. Here is
how I propose things went...
4. We start off with pre-Archeopteryx, a small, bipedal
theropod with forelimbs like those of Coeleurosaur. It
has an insulating coat of feathers.
5. Pre-Archeopteryx discovers that plants, crustaceans, and
even the occasional fish along the shore are delicious.
This discovery may have been accelerated by climate
change which reduces food supply away from the shore. In
pursuit of its food, it starts spending more and more
time in the water.
6. What happens to land-dwelling vertebrates that start
spending a lot of time in water? Riiiiiiiight! Their
limbs tend to evolve into flippers. Our feathered,
bipedal, theropod's forelimbs start looking like wings.
Part way through the process, it will still have some
claws on the leading edge of the flippers. Since it
still spends some significant time on land, it's feet
will still be that of a land animal. It's a bird, it's a
plane, no it's our friend Archeopteryx.
Things start making sense now. The reason that we find
Archeopteryx's fossils only in a lagoon, is because it
was a flightless feathered theropod that spent quite a
bit of time in water. A flightless bird/theropod that
spends a lot of time in water doesn't have to worry
about shedding teeth to reduce weight. Claws on its
wings can be used to grab fish or other prey. The fact
that its feathers aren't suited for flight is moot.
Their purpose is to keep the animal warm, and not get
in the way when it runs around in the water. What
little swimming it does probably consists of breast-
stroke or dog-paddle, because it doesn't have bird-type
shoulder joints.
7. A few million years pass. After spending even more time
in water, adaptations continue. The feet get webbed and
the shoulder joints evolve to a bird-like mode to allow
raising its forelimbs above its shoulders. This allows a
more powerful underwater swimming stroke; actually
"flying underwater". To supply the necessary power, it
needs stronger muscles, and a place to attach them to
(keelbone). Now that it's wings are used for "flying
underwater", "flight feathers" start to be an advantage.
Since it hasn't yet flown aerially, there is no
advantage to shedding its teeth. Hesperornis would be a
reasonable specimen of this stage. Our flightless bird
spends a lot of time "flying underwater". It learns to
navigate in 3 dimensions, which will be important later.
The Avian Kitty Hawk
--------------------
A Hesperornis-like "flightless" bird is minding its own
business one day when along comes a big fish, or whatever,
that thinks of our bird friend as a yummy meal. It gives
chase and the bird flees, with rapid frantic wing-strokes.
Since it's an air-breathing animal, it needs to surface to
breathe. It's moving as fast as it can to escape its
predator, so that it not only gets to the surface, but
most of its body gets clear out of the water. Since it's
being pursued, it keeps flapping its wings... and flies
several metres before landing back in the water, giving
itself enough of an advantage to get to shore safely.
Having discovered flight and its survival value, water-
birds were able to able to parlay their "underwater-
flying" skills to aerial flight. Crash-landing in the
water after getting one or two metres into the air is a
lot less likely to kill/maim a bird than crash-landing on
hard land. Landing on floating logs, and then on branches
of floating logs will be the next step in acquiring tree-
landing skills, without killing themselves if they don't
do it exactly right the first time.
Birds didn't evolve aerodynamic feathers for the purpose
of aerial flight, they evolved hydrodynamic feathers for
the purpose of underwater flight; yeah, picky, picky,
picky. Yes, I have read Elaine Morgan's book "Descent of
Woman". Read into that what you will.
--
Walter Dnes; my email address is *ALMOST* like
[email protected] Delete the "z" to get my real
address. If that gets blocked, follow the instructions at
the end of the 550 message.