April 14, 2006 — Swedish scientists have found half-billion-year-old droppings thought to be from an aquatic worm and hope the discovery will contribute to the understanding of prehistoric ecosystems, researchers announced on Wednesday.

"We have found fossilised excrement dating back 500 million years," Lund University researcher Fredrik Terfelt told AFP.

"This is a unique discovery, at least in this part of the world," Terfelt said, adding that older coprolites, as fossilised dung is known, dating from the Cambrian period of 542-500 million years ago have been found in China.

Terfelt's team has not been able to confirm which animal produced the droppings, but thinks it may be from a small worm belonging to the chaetognath family, an aquatic worm known as an arrow worm which could grow to 10 centimetres (3.9 inches) in length.

"We do not know much about ecosystems that are this old, so this find will give us an idea of how organisms interacted," Terfelt said.

For example, the discovery shows that the worm exclusively ate two types of small invertebrates.

The shape of the fossil, its clear demarcation from surrounding rocks, its density, and high phosphorus content all suggest that it is excrement, Terfelt added.

The discovery was made in 2003 in Andrarum in the southeastern province of Skaane, but "was left on a shelf" and it was only six months ago that researchers began to study it, Terfelt said.

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