Viable hypotheses about the origin of birds and flight have developed.
New evidence and useful information keeps on coming in from all kinds of sources
that we couldn't anticipate. And all this information gets incorporated and
we keep testing it to see which models make the most sense. Sometimes our
entire concept of the problem changes completely. Thirty years ago there was
no viable hypothesis about the origin of birds. Now there's lots of evidence
that they evolved from theropod dinosaurs. Until recently we cast the origin
of flight problem as a dichotomy between the trees and the ground, but we're
moving past that. This is actually how science works.
Much better data are available on the flight stroke.
In 1985, Jacques Gauthier and I first hypothesized that maniraptorans like
Deinonychus had nearly all the equipment necessary to perform a motion very
much like the flight stroke. And, although Deinonychus was not a bird and
was too big to fly, it gave an example of an animal closely related to birds
that could do this.
)
Since
then, smaller long-armed maniraptorans have been found. And other workers
like Alan Gishlick and Steve Gatesy have studied maniraptoran forelimb motion
more intensively. Their conclusions are very much in line with ours.
Click on the Deinonychus arm at right to see a reconstruction of the motion.
New observations of birds cast new light on the flight debate.
There's some great new work by Ken Dial that suggests a whole new take on
the flight debate. Ken found out that young partridges and quail less than
two weeks old can run straight up tree trunks and other vertical surfaces,
using only their hind limbs! Their flapping wings seem to work as "spoilers"
that keep them on the surface. Both adults and young prefer to run up trees
and other inclined surfaces (such as boulders or cliffs), rather than flying
to the top. The little birds flap their developing wings while they run, but
in a slightly different way than the adults do when they fly. As they do so,
they're able to ascend to refuges for safety.
Watch the young chukar ascend a vertical surface.
Choose to view it as a:
These new observations of birds suggest new interpretations.
If this is right, and if bird ancestors could do this, then it suggests several
possibilities. One is that, if bird ancestors went through a tree-living stage,
they may not have needed to climb trees with all four legs. Another possibility
is that they could have generated enough thrust to run along the ground even
faster by flapping their wings—and this would help the "ground up" model.
But oops—I forgot! We don't really need that dichotomy any more. Ken's
work is important—among many reasons—in showing the kinds of aerodynamic
forces that even young chicks with little wings can generate. No one seems
to have noticed this before.