IT STARTED with a postcard-sized photograph of a fossil. Ji Qiang, director
of the Chinese Geology Museum in Beijing, had named it Sinosauropteryx
(China’s winged lizard). The world’s press called it the “feathered
dinosaur”—a crucial missing link between birds and their dinosaurian
ancestors. The photo showed a small creature with what looked like a frill of
feathers running along its back. But photos can mislead, and four leading
Western palaeontologists wanted to see for themselves. So in March they
travelled to China.
They were right to be sceptical. Examining the fossil at the Beijing museum,
the visitors discovered that the “feathers” were no more than thin, stiff
filaments which lacked the branching pattern of modern feathers. But the
disappointment ended there. On the first day of their visit, Ji smilingly
presented them with a “special animal” which he called Protoarchaeopteryx,
a close relative of Archaeopteryx, the first bird (see “The Early Bird”).
He followed this up with case after case of
fossils, from dragonflies to dinosaurs. At the Nanjing Institute of Geology and
Palaeontology, 900 kilometres south of Beijing, there was more.
But these amazing collections were nothing compared with the fossils the four
palaeontologists saw still embedded in the Yixian formation in rural Liaoning
Province. One week and 80 rolls of film later, they left China, still reeling
from the impact of what they had seen. “This has to be one of the most important
palaeontological sites in the world,” says an awe-struck Larry Martin of the
University of Kansas, Lawrence. And it will keep palaeontologists busy for a
century, predicts Yale University’s John Ostrom.
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For anyone interested in ancient bones, China is now the place to be. The
Academy of Natural Sciences in Philadelphia, which sent Martin and his
colleagues, is funding a bigger expedition. This month, a team assembled by Don
Wolberg visits the Yixian formation with Chinese scientists to collect fossils
and gather geological data to find out more about how the area would have looked
when the fossils were laid down. A Nova television crew is travelling with them.
The American Museum of Natural History in New York is also negotiating to send
its researchers to the site. Meanwhile, China’s own palaeontologists have posted
a guard at one critical fossil location and begun systematic scientific
excavations instead of relying on finds by local farmers.
The excitement reflects the rarity of the Yixian formation. Normally, only
the bones of land animals survive, and even the bones of giant dinosaurs are
often only fragments. The Burgess Shale in Canada and the Solnhofen Limestone in
Germany are international treasures because they hold unique impressions of
animal bodies. A century and a half of excavation at Solnhofen has yielded seven
Archaeopteryx skeletons and a lone feather, but in just a few years,
farmers from Liaoning Province have uncovered hundreds of early birds, called
Confuciusornis. And they have still barely scratched the surface.
All life is here
Many fossils from the Yixian formation are exquisitely preserved. There are
the feathers and delicate bones of small birds, skin imprints, plants and
insects. “These are probably the best dinosaur specimens that have ever been
collected,” says Martin. “There are lizards with full skin and mammals with
hair.” In addition, the fossils come from “a period of time quite different from
anything else anywhere in the world”, says Ostrom. They date from 150 to 120
million years ago in the late Jurassic or early Cretaceous, when birds, modern
mammals and the first flowering plants were at critical points in their
evolution. “The world we live in was being invented,” says Martin.
The condition, variety and abundance of fossils is staggering. In Beijing,
Ostrom, Martin, Peter Wellnhofer of the Bavarian State Museum in Germany and
Alan Brush of the University of Connecticut were showed a parade of specimens
which included pterosaurs, dinosaurs, fish, insects, mammals and plants, many
new to science. Dave Bubier, director of special projects at the Academy of
Natural Sciences, took numerous photographs for later study.
The next stop was Nanjing. The rock containing the Sinosauropteryx
fossil was split along the plane of the bones, giving two impressions of the
animal. The Beijing museum bought one and the other went to the Nanjing
Institute of Geology and Palaeontology. It was a photo of this fossil that
triggered great excitement last autumn at the Society of Vertebrate
Palaeontology meeting in New York.
But by March, Nanjing Institute’s Chen Pei-Ji had a much more impressive
specimen to show his visitors. The latest Sinosauropteryx is larger
than the first, and so well-preserved that the pale ovals of two unlaid eggs are
discernible inside its body—something never seen before in a dinosaur. It
also contains the jaw of its last meal, a shrew-sized mammal which Ostrom thinks
may have been a triconodont. Palaeontologists have long believed that some small
dinosaurs dined on mammals, but this is the first direct evidence.
The visitors were then shown another dazzling collection of fossils. By now
they were itching to see the Yixian formation for themselves. Travelling with
Ren Dong of the Geology Museum, they took an overnight train from Beijing to
coastal Liaoning Province and then drove three hours in a car into the stark,
semiarid badlands. Here streams cut through the hills, exposing the Yixian
formation which was once the bed of a freshwater lake. Local farmers have known
about the fossils for years, but they only recently discovered that scientists
and smugglers will pay for them
(“Psst . . . wanna Triceratops?”, New Scientist,
14 December 1996, p 12). Even now, no one is sure exactly how
extensive the fossil-rich zone is. Chen estimates that it may extend tens of
kilometres.
Ren spends three months a year in the area where Sinosauropteryx was
found. The Western scientists visited this site and another where a stream has
exposed a rich bed of insect fossils. The abundance of Yixian fossils amazed the
visiting palaeontologists, who were accustomed to digging through large piles of
rock before finding anything. “Everything has fossils in it,” marvels Martin.
Brush comments that fossil birds seem more abundant there than living ones.
While they were in the field, Ren picked up what looked like a fossil flower. If
it is a true flower, it is the oldest known.
A top priority for the team was collecting geological data, to learn more
about the ancient environment. The lake was absolutely becalmed, says Martin.
Extremely fine silt settled on the bottom, burying dead animals that fell into
the water. Gas from erupting volcanoes nearby may have killed large numbers at a
time. The result is a pale siltstone, interrupted by layers of ash and teaming
with fossils. In total, the sediment layers are about 1300 metres thick—no
one knows how many years that represents.
The age of the Yixian formation is controversial. The chronology of this
geological period is usually based on the succession of marine fossils, but they
are missing from the lake deposits. By comparing local fossils, Chinese
geologists place the formation in the late Jurassic, which ended 145 million
years ago. Some Western scientists believe it is younger, dating back to the
early Cretaceous, because the birds appear much more modern than
Archaeopteryx. Hoping to end the controversy, the visiting palaeontologists
took samples of volcanic ash back to the US for argon-argon dating using
instruments not available in China.
East meets West
Following this trip, other palaeontologists from the US and Europe are
clamouring to visit China. And the Chinese are eager to cooperate. “This is not
only a Chinese treasure, but a global treasure,” says Ji. Western institutions
can provide the money, equipment and infrastructure sorely needed in China. Even
electrical sockets are in short supply at the Geology Museum and the Nanjing
Institute, limiting the use of microscopes. A lack of artificial lighting meant
that Bubier had to take specimens outside to photograph.
Scientific expertise is also lacking. Few Chinese have the skills required to
prepare fossils. Wolberg wants to send Western fossil preparers to train Chinese
technicians and equip them with the tools needed for this delicate work. China
also has few specialists in vertebrate palaeontology. But by collaborating with
outsiders they hope to resolve key questions by comparing Chinese fossils with
other specimens, such as Sinosauropteryx with Compsognathus
from Europe.
These are exciting times for palaeontologists. The wealth of material coming
out of the Yixian formation is overwhelming. On the final day of their visit to
the Beijing museum, Brush and his colleagues attended the opening of a new
display. “I realised that I was standing with more feather fossils from Mesozoic
[dinosaur-age] birds than there are in all the museums of North America,” he
says.
* * *
The early bird
DISCOVERIES in China’s Yixian formation are revolutionising our understanding
of avian origins. And the picture turns out to be much more complicated than
palaeontologists had thought.
Despite its poorly preserved skull, Protoarchaeopteryx shows the kind of
mosaic of bird and dinosaur features that would be expected in a transitional
form. It has the long legs of a fast runner, arms resembling Archaeopteryx and
much more prominent teeth—which are smooth like those of Archaeopteryx,
not serrated like those of dinosaurs.
Scientists at the Chinese Geology Museum in Beijing believe
Protoarchaeopteryx was a forerunner of the smaller Archaeopteryx. Peter
Wellnhofer of the Bavarian State Museum in Germany agrees that the two are
closely related. But he adds: “I can see no way that Protoarchaeopteryx was an
ancestor of Archaeopteryx because [dating shows] it must have been several
million years younger.”
Evidence on the crucial question of whether Protoarchaeopteryx had feathers
is ambiguous. “I would expect that there were feathers connected to these kind
of forelimbs, but there are no flight feathers preserved or visible,” says
Wellnhofer. There are three tail feathers, but they look more modern than those
of Archaeopteryx and are not clearly attached to the fossil, so they may come
from another bird.
The sheer range of birds in the Yixian formation is also puzzling.
Confuciusornis comes from slightly younger rocks than Protoarchaeopteryx, but
the time difference seems too small to account for the evolutionary changes.
Confuciusornis has some primitive features, such as detached ribs like those of
dinosaurs, but it has a beak, its wings look modern and its tail bones have
fused into the stubby pygostyle found in most modern birds. The experts suspect
that it was a member of a group that was widespread for a time but did not
survive past the end of the Cretaceous.
Several other birds from the Yixian formation have teeth and all have leg
bones that fuse differently from modern birds. Palaeontologists are scratching
their heads and hoping that more fossils and a better understanding of the
sequence of the rocks will help them understand this burst of avian
evolution.
- Further reading: for more on the Yixian fossils see
http://www.dinofest.org/china/index1.html