Missing Members of a Living Museum

Cracks in the Earth's crust deep below the sea may not be as secure a refuge for weird life-forms--worms, mollusks, and other ancient species--as scientists had thought. Russian fossils, described in tomorrow's issue of Nature, suggest that broad groups of hydrothermal vent creatures have gone extinct. The find undermines the view that vent communities have remained relatively unchanged for hundreds of millions of years.

Crispin Little and his colleagues at the Natural History Museum in London examined fossils deposited 438 million years ago at the dried-up Yaman Kasy vent in Russia's southern Urals. During the Silurian period, this region was at the bottom of an ocean. Little's group noted the usual menagerie of deep-sea vent organisms, such as tubeworms and bivalve mollusks. But they also found fossils of filter-feeding lampshells (brachiopods) and snaillike grazers (monoplacophorans) that do not appear to have been present in other vents of that time or in modern ones. According to Little, "Modern vent communities are not refuges for these Silurian shelly taxa," or species groups.

But some experts point out that the same fossil record confirms that some groups, at least, indeed have found sanctuary at vents. "Some taxa only occur at vents and are unique," says Cindy Van Dover, a marine biologist at the University of Alaska. The existence of these groups, she says, "is a good argument that the vents serve as a refuge for them." Nevertheless, some of the world's most isolated habitats appear to be at best an incomplete living museum of ancient life.