Spectacular Fossil Discovery: 100 Years Later

WASHINGTON (ISNS) -- At the base of a ridge in the Canadian Rocky Mountains lie the types of fossils that make geologists giddy, the remnants of a flourishing undersea world from more than 500 million years ago. They are preserved today in a rock layer called the Burgess Shale near the town of Field, British Columbia. This year marks the 100th anniversary of the discovery of the shale and its astonishingly well-preserved fossils, revealed by Smithsonian Institution paleontologist Charles Walcott in late August, 1909.

For those uninitiated into the world of ancient time and long-lost fossils, the shale appears to be nothing more than rocks layered and stacked into mountains. But the late paleontologist Stephen Jay Gould summed up the importance of this rock formation to science in his bestselling book "Wonderful Life: The Burgess Shale and the Nature of History." The shale, he said, contains "the world's most important animal fossils."

Most animal fossils consist of hard parts like shells, teeth and bones that are less likely to decay and rot away than soft tissue. But the Burgess fossils, despite hundreds of millions of years of geological processes crushing, twisting, and heating them, are extraordinarily well-preserved, with soft tissue such as eyeballs and guts transformed into rock. In the century since this discovery, only a few other high quality soft fossil sites have been found around the globe.

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The formation lies next to the bottom of what was a submarine cliff more than 505 million years ago. The area where the fossils rest was deep enough under water that waves or storms did not disturb the sediments that buried the animals. It is generally agreed that repeated flows of mud buried numerous groups of living or very recently dead animals over the course of about 100,000 years. The mud and low levels of oxygen within it stopped the decay process that would usually destroy the animals' vulnerable soft parts. The animals' structures have been maintained through the long history of intensive processes that solidified the sediments into rock and built the Rocky Mountains.

Just how that happened is not completely clear. Paleontologist Alex Page from the University of Cambridge in England recently developed a new theory, that the layers of clay surrounding many of the Burgess fossils did not form immediately after the animals were buried, but tens to hundreds of millions of years later, challenging the understanding of what exactly protected the soft parts of the animals.

In March, Daley published an article in the journal Science describing an animal called Hurdia. When Walcott first looked at the fossil, he thought the mouth parts were a jellyfish, the front legs were shrimp, the main body a sea cucumber, and a tear-drop shaped shell, another animal. "It's totally strange," said Daley, who described the last piece as three sides of a rectangular box, sticking out in front of the mouth and head.

While studying the tear drop structure, which she calls a carapace, Daley checked to see if it fit over the rest of the body, where it might have provided protection. "There are these little notches at the posterior side of the carapace where the eyestalks stick through," she said. "So if the carapace had slid forward that would mean the eyes were growing out of the posterior end." Daley thinks that the structure stuck out in front of Hurdia's head and was somehow related to the collection of food as a sort of digging tool or funnel.

Caron explained that the process is like a Martian trying to draw a three dimensional picture of human anatomy based on only two dimensional views of human bodies. If the entire front side of a human fossil were facing the Martian directly, figuring out the original shape of nose would be difficult, because it would be squished. The problem might be solved by looking at other humans found in different orientations that could reveal more about the shape of the nose.