Mark Norell: North-eastern China 150 million years ago was a
remarkable place. It was a temperate forest, basically, it was an area which had
a number of large lakes and small lakes and it had volcanoes going off in the
general area, so there was constantly volcanic ash raining down on things, which
made ideal conditions for preservation of small lakes. It also is ideal
preservation in the sense that it preserves parts of the animals which we don't
usually get. For instance, we have soft tissue preservation, including things
like feathers, things like hair in mammals, things like the claw sheaths on
animals, so that we really get this remarkable preservation which we only get in
a few other places in the world.
Robyn Williams: How fine in detail are those feathers?
Mark Norell: The feathers we can see quite a bit.
Unfortunately we can't see everything we would like to see in them because we're
not really looking at the fossilised feather. When you see the imprint of the
feather in the rock you're looking at the bacterial decomposition products of
the decomposition of that feather. So the feather, you can make out the
structure, you can see the shaft down the middle which is called the rachis, you
can see the blades which are composed of single filaments which are called
barbs, and in some cases we can even make out the barbules which are just
microscopic little hooks that allow feathers to be able to self-organise, so
when you take a feather and you mix it all up and then you can pull it back and
zip it back into shape. These animals had those characteristics also.
Robyn Williams: The big question is what were those feathers
for in the beginning?
Mark Norell: The most primitive feathers that are found in
the more primitive dinosaurs don't look like feathers at all, instead they look
more like hairs. But unlike hairs they're hollow, so they have a lot of the same
characteristics that feathers have but they covered the entire body, and they're
just small...some people have called them dino-fuzz. We refer to them as
proto-feathers, but they're a uniform body covering over the entire animal. If
you think that living birds today, feathers are used for a variety of things,
they're not just used for display, they're used for camouflage, they're used as
aids in hunting, they're used to help brood the nests, but most importantly
they're used for insulation. Just like we even use bird feathers today in
insulation in down coats and things like that, the insulation component is very
important.
So when you see a bird hatch, it doesn't have big feathers for flight or
display but they're completely covered with downy feathers which are for
insulation. So I think we can make a pretty good argument that feathers
originated as insulatory coverings for birds and then as we continue up the
evolutionary tree and get closer and closer to birds these feathers were then
elaborated into some of the different feather types that we see today, you know,
everything from the primary wing feathers which are asymmetric, which have
neurodynamic function, to feathers which exist on the tails that we see in the
non-avian dinosaurs also in these tail fans which were probably for display, and
feathers which have all sorts of different uses in modern birds.
Robyn Williams: And of course most structures in animals,
plants for that matter, tend to have a number of uses. But the question of
flight has been argued about for some time. Was it something that was developed
straight away or was there a process which was far more to do with escaping your
enemies, so that you're running on the ground and somehow the wings and indeed
the feathers helped you escape rather more quickly? Was that the beginning of
the process, do you think?
Mark Norell: Certainly if we talk about flight that's
present in modern birds, like the ones we can see out my windows, that sort of
flight comes really pretty late in the evolutionary story and doesn't have much
to do with the origin of what we would call volant capability, which is just the
ability to get up in the air a little way. If you look at the early bird story
and what has been called the archetypal early bird, archaeopteryx, if it had any
volant capability it was a pretty poor flyer and in no way, in my mind, could
fly like a modern bird flies. However, if we talk about the origins of flight
itself, I think that a good argument can be made for escape, for predator
avoidance.
I think there's been a lot of very interesting work done by Ken Dial and his
group in Montana on just what this fright and flee mechanism is. They refer to
it as wing-assisted running or wing-assisted incline running, and they can see
it modern birds and they can see it in hatchlings of modern birds, when, even
before they're fledged, when they'll run, and then as the same time as they run
to get added momentum is they'll flap their wings. Sort of like a sprinter
running and using his arms to move to increase momentum. Certainly early birds I
think did this and I think that we can see that in juvenile birds today. It is
predator avoidance and stuff. I mean, you scare these things and then they go,
and they're incapable of flight but they flap their wings, they can go vertical.
Robyn Williams: So what was archaeopteryx doing? Was it
gliding, was it just hopping in the air?
Mark Norell: We can never tell for sure because we can't
study behaviours of animals which have been extinct this long. The feathers of
archaeopteryx, just like the feathers of some more primitive dinosaurs, things
like microraptor and stuff, they show this asymmetrical pattern that suggests
that they were used for some aerodynamic activity. Nevertheless, if
archaeopteryx could fly he was probably a pretty poor flyer because if you think
of the physics of flight, one has to be able to transmit force which is
generated by the wings moving down to the air and to the ground, to be able to
compress that to be able to generate up-force for the animal to fly. So if you
want to be efficient in doing that you want all of the force which is generated
by the wings to be transmitted downward.
Archaeopteryx simply couldn't do that because its body was built sort of like
a slinky. If you took and you compressed the wings down, a lot of what would
happen is just that the bones would just move around. It would be sort of like
when you pick up a cat or something, it's going all over the place. It's not
until we get much later in the evolutionary tree to an animal called
confuciusornis where we get the kind of rigidity in the skeleton that one sees
in a modern bird, which would be very efficient for it to have a down-force and
then be able to actually transmit all the force from the wing beat to the air to
be able to fly in somewhat of a similar fashion to what we see in pigeons or
something today.
Robyn Williams: What did the confuciusornis look like?
Mark Norell: Confuciusornis was a small bird. It had a beak,
it was the first bird to have a beak, it didn't have teeth. It had sort of a
plump body, sort of like a partridge or a quail. Its wings weren't
extraordinarily long, however its wing feathers were very long. So it lacked a
true bony tail the way that a non-avian dinosaur or even archaeopteryx had, but
it had a couple of big, long feathers that stick out the back that can be twice
as long as the body itself, sort of like a tropic bird or a bird of paradise.
When we find confuciusornis, those long feathers are only in a fraction of
the animals that we find, and sometimes we can find many animals that are
preserved in the same slab suggestive that they were killed by a gas cloud from
a volcano or something and a whole flock fell in, and not all of those will have
the long tail feathers. So there are inferences that have been made that perhaps
these are males, like the same as in living birds today which the males usually
have more spectacular plumage than the females do.
Robyn Williams: Mark, what's your own line of research in
this field?
Mark Norell: Really what I...I shouldn't say 'I' but my
group, including my students and my colleagues and stuff in China and elsewhere,
what we are interested in looking at is the transition from what people have
traditionally called dinosaurs to what people have traditionally called birds. I
think that over the last 20 years that line has really been blurred. It's very
similar to human evolution when 100 years ago it was pretty clear what was human
and what was non-human, because basically you had modern humans and you had a
few cavemen fossils kicking around Europe, but with the great discoveries,
especially from east Africa, of Australopithecus materials, the Homo erectus
stuff from central Asia and everything else, the line between what's human and
non-human has really blurred, to the point even that it's something which some
anthropologists won't even talk about because you can't even really define
it.
Well, similarly in the colloquial name 'birds' also...we used to think that
birds are special because they have feathers, they have wish bones, they have
hollow bones, they brood their nests, they have an advanced socio-biology, they
have all these other sorts of things, an advanced metabolism. Well, all of those
attributes which I just named are now found in non-avian dinosaurs. We have
evidence that tyrannosaurus was feathered. We have evidence that non-avian
dinosaurs like velociraptor and oviraptor and stuff sat on their nests and
brooded them. We know that tyrannosaurus rex, as well as much more primitive
therapods than it, had wish bones. So all these attributes are being forced
further and further down the tree which is just giving us a very, very different
picture of how birds were put together and some of the evolutionary
modifications and the timing of those modifications, which arguably at 10,000
species is the most successful vertebrate terrestrial group on the planet.
Robyn Williams: When you go across from the museum here to
Central Park and you look at the pigeons and other birds, what do you think of
them?
Mark Norell: Actually it depends on the bird. The pigeons, I
wish they'd go away! But I don't think about it that much but I like to think
that the work that my group has done, that we've given a new appreciation for
birds and really shown them to be what they are; living dinosaurs.
Robyn Williams: Mark Norell, curator of fossils at the
American Museum of Natural History in New York.
http://www.abc.net.au/rn/scienceshow/stories/2009/2545603.htm
