August 16, 2007—A rare "treasure trove" of ancient sea spiders found in France fills a 400-million-year gap in the mysterious creatures' spotty fossil record, scientists say.

The well-preserved marine animals, called pycnogonids, were unearthed in 160-million-year-old fossil beds at La Voulte.

In a paper published online in the Proceedings of the Royal Society B, a team of French scientists describes 70 specimens—including the one seen above—from three distinct species found in the region's Lagerstätte, a type of sedimentary rock formation.

"This Lagerstätte is very important, because during Jurassic times the water here was about 200 meters [656 feet] deep," study co-author Sylvain Charbonnier told BBC News. The Jurassic period lasted from 199.6 to 145.5 million years ago.

Experts know of more than a thousand living species of sea spiders, which are only distantly related to true spiders (see a photo of a living sea spider found in Antarctica).

But until now fossil pycnogonids have been scant. The latest cache is already helping researchers piece together the unusual animals' evolutionary history.

For example, the ancient pycnogodis appear to be very close in form to their living counterparts, the scientists say, and likely began colonizing the deep sea before the start of the Jurassic.

—Victoria Jaggard

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