SULZER ANALOGY
How the dinosaurs became birds
After conquering the water and the land, the animal world found a
huge additional living environment through flying. However, the way
to the skies required enormous anatomical adaptations.
E
xperts have long puzzled over how birds
developed from their flightless ancestors.
In 1860, workers in a limestone quarry near
Solnhofen found the fossilized imprint of a feather in a
sedimentary layer of rock that was 150 million years old. The
feather was remarkably similar to the feathers of birds of today.
This indicated that there were bird-like creatures at the time
of the dinosaurs.
The researchers’ excited search for the animal to
which the feather belonged met with success a
year later. A skeleton with wings and a long,
feathered, lizard-like tail was found in
the same quarry, and the fossil had
characteristics of both birds and reptiles. With the discovery of this
“primeval bird,” the archaeopteryx,
a link was found at last in the development of reptiles into birds. However,
the anatomical details led to doubts as to whether the
archaeopteryx could actually fly. The strong breastbone that
is typical of birds was not present, which meant that the animal
also did not have the muscular system that is necessary for
flying. The “primeval bird” probably climbed trees and glided
down to the ground again with outspread wings.
The “primeval bird” archaeopteryx
lived 150 million years ago.
Pneumatic bones
and a super-heart
As a further optimization,
birds have five pairs of air
sacs between their skin and
their internal organs that
expand or compress when
breathing. These air sacs are
Lightweight build
directly connected with the lungs and with the air chambers
Anyone who wants to fly has to save on weight wherever
in their hollow bones. Birds thereby have an extensive
possible. The bones of some dinosaurs were already hollow
respiratory system that can constitute up to 80 percent of the
and thin-walled, which kept their weight within limits despite
entire body cavity. Moreover, while mammals only have a
their enormous
single air tube for inhaling and exhaling, the
Feathered ancestors of birds already existed
lungs of a bird work in a continuous-flow
body size. Birds
in the time of the dinosaurs.
mode, so that birds are able to breathe in
also have bones
without any interruptions.
that are filled with
The constant flow of air through the lungs makes it possible
air. As a result, the skeleton of an adult golden eagle weighs
for the bird to fly at high altitudes. On its 14 000 km long
only 200 grams.
nonstop flight, the bar-headed goose flies without any problems
The shape of the bones is also critical. In the 1990s, in the
over the summit of Mount Everest, where the oxygen content
Liaoning province, Chinese paleontologists dug up fossils that
of the air is only one-third of that at sea level. The excellent
belonged to the theropod family. These small, predatory
supply of oxygen allows the birds to operate like a highdinosaurs ran on their back legs. They had also developed a
performance engine. The heart of the hummingbird, for
wrist that could bend to the side as well as a long, folding
example, beats an incredible 1200 times a minute. The superarm — a fundamental evolutionary step on the way to
heart that is necessary for this kind of performance accounts
developing a functioning wing. And, when the dinosaur
feathers developed into the various feather types of a bird — for 28 percent of the weight of the hummingbird. It is therefore
not surprising that the “pumps” in the world of birds work
down feathers for protection from the cold, asymmetrical
flight feathers for propulsion, and tail feathers for steering — at a high operating temperatures of around 42 °C (107.6 °F).
Herbert Cerutti
the path to the heavens became free.
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Sulzer Technical Review 3/2013
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