In 1861, Bavarian quarry workers digging through limestone in southern Germany found a fossil that set off a storm of still unsettled scientific and ecclesiastical controversy.
It was a set of bones, complete with perfectly preserved impressions of feathers, of Archaeopteryx (pronounced ahr-kay-OP-ter-ix). About the size of a crow (1 foot long), at 150 million years old, it is both the earliest bird ever found and the first tangible proof that birds descended from dinosaurs.
On Saturday, for the first time in history, an Archaeopteryx fossil will be on display in America, at a special exhibit at the Field Museum of Natural History.
The old bones are so rare and highly valued that security and logistical precautions surrounding the visit resemble those made when museums of fine art send out their Monets, Michelangelos and Picassos on temporary loan. The fossil will be under armed guard 24 hours a day.
That is because, since 1861, just five other Archaeopteryx fossils have turned up. Each is so jealously guarded that their respective owners have never before risked letting one travel overseas.
“This is a once-in-a-lifetime opportunity,” said Field Museum paleontologist Olivier Rieppel. “It’s a very rare and extremely important fossil–one of the most famous in the world.”
Its visit coincides with the 57th annual conference of the Society of Vertebrate Paleontology, an international meeting of 900 scientists held by the museum Oct. 8-11. The fossil will be on display through Oct. 19.
The discovery of the first Archaeopteryx fossil in 1861 is regarded as a landmark in paleontology, coming just two years after Charles Darwin published “Origin of the Species.” Archaeopteryx was the first fossil evidence supporting Darwin’s theory of evolution and transitional species, new groups of organisms evolving from an older group, in this case birds from dinosaurs.
Darwin’s theory challenged religious orthodoxy, which maintained God created all things. Even today, religious fundamentalists reject the notion of plants and animals evolving from primitive forms to more complex ones, and the teaching of evolution has continued to generate controversy in many school systems.
While it’s here, Archaeopteryx will be the center of plenty of heated scientific debate. Various groups of paleontologists continue to argue over how Archaeopteryx is related to dinosaurs, whether it could fly and the method by which the first primitive birds learned to fly.
The fossils of the primitive birds are as striking and mysterious today as the day the first was discovered. Feather patterns of modern flying and flightless bird species differ radically, and Archaeopteryx bore the feathers of a flying bird, though nobody knows if or how well it could fly.
Its physical characteristics are as much reptilian as they are avian. Like most reptiles, it has teeth, a long, bony tail and clawed, grasping hands.
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Take away Archaeopteryx’s feathers and wings, and its anatomy bears a striking resemblance to a group of two-legged, warm-blooded dinosaurs known as theropods, especially the much bigger, speedy carnivore velociraptor.
But the astounding fossils of Archaeopteryx, showing perfect impressions of its feathers and wings, clearly establish it was a primitive bird.
“Bird fossils with feathers are rare elsewhere because the conditions necessary for the preservation of feathers are very unusual,” said John Flynn, chairman of the Field’s geology department.
Archaeopteryx lived in an area of southern Germany when it was a shallow, reef-strewn tropical sea 150 million years ago.
When they died, they sank to the bottom of deep, stagnant lagoons sheltered from open seas by the reefs.
“Not even severe storms could stir the bottom water layers of the lagoons,” Rieppel said. “That produced very fine-grained silt on the lagoon bottoms that eventually compacted to very fine-grained limestone.”
Carcasses of dead animals that sank into that muck were extremely well-preserved. With no oxygen, there were no scavengers down there to rip them apart and very little bacteria to fuel decomposition.
Those reef areas millions of years later were lifted by geological forces above sea level.
With the advent of printing, the limestone, a deposit covering a 516-square mile area near Solnhofen, Germany, became highly prized. It was quarried by hand, slab by slab, providing plates for extremely detailed lithographic printing.
Quarry workers occasionally would come across 150-million-year-old fossils that preserved impressions even of soft tissues of insects, crabs and jellyfish.
Among them have been the feathered impressions of six Archaeopteryx, the most recent one found in 1992, which is the specimen coming to Chicago.
The specimen coming to the Field belongs to the Bavarian State Museum of Paleontology, in Solnhofen.
A curator from the Bavarian museum will accompany the fossil on its airline flight, arriving late Thursday in Chicago. He will oversee its installation in the temporary exhibit, and remain here until it goes back to Germany.
The Field Museum has agreed to insure the borrowed fossil for an undisclosed but “considerable” sum against damage or loss during its Chicago sojourn, said Rieppel.
Greg Septon, a bird taxidermist for the Milwaukee Public Museum was able to use the remarkably detailed fossils to construct a feathered model of Archaeopteryx that will be used in the exhibit.
Septon took plumage and body parts of seven living species of birds that most resembled those of Archaeopteryx, including cormorant and partridge feathers. Looking for modern counterparts to its teeth, he settled on trout teeth.
British biologist Thomas Huxley first established the link between dinosaurs and birds in the 1870s. A hundred years later, in a 1976 study, Yale University paleontologist John Ostrom established a firm link between Archaeopteryx and theropods by comparing their skulls and skeletons.
“This was the landmark study that showed Archaeopteryx is related to theropod dinosaurs,” said Rieppel.
Nonetheless, Archaeopteryx continues to be at the center of ongoing arguments over both the origin of birds and the nature of evolution, he said.
Some scientists argue that birds evolved directly from dinosaurs, others that they evolved independently from dinosaurs, sharing a common reptilian ancestor. Still others maintain that birds are, in fact, living dinosaurs.
Archaeopteryx’s anatomy also has set off a lively, continuing debate on how and why the earliest, most primitive birds first learned how to fly.
One group of experts suggest that Archaeopteryx’s ancestors, “protobirds,” were small, insect-catching predators. They would have been swift-running, leaping creatures that may have evolved feathers to help trap insects. Over time their feathered, outstretched arms began to provide lift to their leaps.
Another group believes the first fliers were winged protobirds using clawed feet and hands to climb trees and cliffs. From there, they could jump and spread their wings to glide or parachute to the ground, later learning to flap and propel themselves.
“This question of whether Archaeopteryx could fly or not relates to the origin of feathers,” said Flynn. “Did they evolve for flight, or first for insulation, and only later becoming further adapted to enable flight?”
What makes answering the questions about Archaeopteryx and birds and dinosaurs difficult is the fact that nature left so few fossils behind.
“Darwin knew there had to be intermediate steps in evolution,” Rieppel said. “He could predict transitional species, but when he wrote `Origin of the Species,’ he had no fossil record of one. Then, two years after he wrote it, along comes Archaeopteryx.”
Peter Wellnhofer, the curator who is coming with the Archaeopteryx fossil from Bavaria, is a renowned expert on the primitive bird and on pterosaurs, ancient flying reptiles. He will give a public lecture at 2 p.m. Saturday, Oct. 18.
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The fossil should attract many of the scientists here for the paleontology meeting.
“As famous as Archaeopteryx is,” said Rieppel, “this will be the first chance for many scientists here to see an actual fossil of one.”