Embryos Dating Back 500 Million Years Revealed With X-Rays

Richard A. Lovett
for National Geographic News

August 9, 2006

Using the world's largest microscope, paleontologists have peeked inside tiny fossils of 500-million-year-old embryos, each about the size of a grain of sand.

"These are extremely rare," said Philip Donoghue, a paleontologist at Britain's University of Bristol. "Studying them is a problem."

Previously the only way to find out what was inside such fossils was to slice them open and put them under a microscope.

Even if scientists were willing to do that, many fossils would be destroyed in vain. That's because most embryo fossils preserve only the outline of the animal, with nothing inside.

"But a few are really well preserved," Donoghue said.

The new technique allows the fossils to be scanned without damaging them.

Donoghue and his team report on their research in the current issue of the journal Nature.

World's Biggest Microscope

The fossil embryos were found in China and Siberia and are members of wormlike ancient species called Markuelia and Pseudooides.

(See the National Geographic magazine feature, "China's Fossil Marvels.")

Using the new technique, researchers have been able study the animals at a level of detail never before possible.

For example, Donoghue says, it's possible scan the length of a tiny worm's digestive tract, determining the shape of its organs and the arrangement of its teeth.

These clues are useful in determining how closely the animals are related to modern species.

In order to find enough fossils to examine, Donoghue's team went back to areas where embryo fossils had been discovered by chance.

"We pull out tons of rock and pick through every little sand grain and decide if it's rock or an embryo," he said.

"On one site, my colleagues picked through 12 [metric] tons [26,000 pounds] of rock and found only 500 embryos."

Donoghue's microscope is at the other end of the size scale.

The instrument uses extremely powerful x-rays generated by a particle accelerator a quarter-mile (four tenths of a kilometer) wide. It functions somewhat like a hospital's CT scanner, but it uses much higher-energy and "purer" x-ray sources.

"It's a fantastic new technology using the word's biggest microscope to look at the word's tiniest fossils," Donoghue said.

Doug Erwin is a paleontologist at the Smithsonian Institution in Washington, D.C. He said the study is "beautiful work and provides an exciting new way of studying some of the most important early animal fossils."

Donoghue's team is already starting to turn its new tool on other types of fossils, including seeds, flowers, and brain cases.

"We're probing the limits of fossilization," he said. "We're seeing features we never thought would be preserved because they're so small."

But the technique also reveals that there's no reason to go to even more powerful imaging methods.

With the new tool, the scientists can see the fossils of individual hairs, but when they try to look inside they find no additional details.

"So we know where the limit is," Donoghue said.

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