By Ker Than
LiveScience staff writer
Updated: 9:02 p.m. ET Sept. 22,
2006
The earliest known bird had flight feathers on its legs that
allowed it to use its hindlimbs as an extra pair of wings, a new
study finds.
The finding, detailed in the current issue of the journal
Paleobiology, supports the theory that early birds learned to glide
and parachute from trees before achieving full-fledged
flight.
"This paper puts forward some of the strongest evidence yet that
birds descended from arboreal parachuters and gliders, similar to
flying squirrels," said study author Nick Longrich, a doctoral
student a the University of Calgary in Canada.
The missing link
Archaeopteryx was a crow-sized animal that lived about 150 million
years ago and which looked like a cross between a bird and a
dinosaur. It had feathers and a wishbone like birds but also
reptilian features like a long bony tail, claws and teeth.
When the first Archaeopteryx fossil was discovered in 1861, it
caused a sensation because it was the kind of transitional animal
that the British naturalist Charles Darwin predicted in his theory
of evolution only a few years earlier.
In 1877, a second Archaeopteryx specimen discovered in Germany
showed a curious feature: long feathers covering its hindlimbs. For
more than a century, the feathers were dismissed by most scientists
as being simple, albeit unusual-looking, insulating body
featherscalled "contour" feathersthat didn't play a role in the
animal's flight.
But then, beginning in 2002, paleontologists began finding
four-winged dinosaurs in China with hindlimb feathers that appeared
to be important for gliding and perhaps even flying. In light of
the new findings, Longrich decided it was time that Archaeopteryx
was reexamined.
Flying with four wings
Longrich examined hindlimb feathers on five Archaeopteryx fossils
using a dissecting microscope and found that the feathers had
features typical of flight feathers in modern birds, including
curved shafts, a self-stabilizing overlap pattern and vane
asymmetry, in which the parallel row of barbs that make up the
feather are longer on one side than the other.
Next, Longrich used standard mathematical models for flight to
calculate how an extra pair of wings would have affected
Archaeopteryx's flight. He found that hindlimb feathers would have
allowed Archaeopteryx to fly slower and to make sharper
turns.
Sharper turns would have improved Archaeopteryx's abilities to
maneuver in pursuit of prey, to escape predators and to fly through
the cluttered branches of trees and bushes. And the ability to fly
slower meant Archaeopteryx had more time to avoid obstacles and to
make safer landings.
Longrich speculates that the hindlimb feathers might have served
other roles in addition to flight. Like modern pigeons, kittiwakes
and vultures, Archaeopteryx's hindlimb feathers might have acted as
airbrakes, or perhaps stabilizers, control surfaces or flaps,
Longrich writes.
Scientists dont know when in their evolutionary history birds
switched from a "four winged" design to a two-wing one, but it's
thought that hindlimb wings were sacrificed in order to free up
legs for other functions, such as running, swimming and catching
prey.
"The idea that a multi-winged Archaeopteryx has been around for
more than a century, but it has received little attention,"
Longrich said. "I believe one reason for this is that people tend
to see what they want or expect to see. Everybody knows that birds
don't have four wings, so we overlooked them even when they were
right under our noses."