Deep ocean is no place to hide.

Far below the waves, in the dark reaches of the sea, underwater gardens bloom wherever volcanic fluids seep from the seafloor. These hot, chemical-laden brines sustain an odd collection of microbes and animals, among them tube-shaped worms, giant clams, and blind shrimp. Because these hidden communities seem completely cut off from the rest of the world, some scientists think seafloor vents have sheltered ancient species that were wiped out in other parts of the globe long ago. A fossil discovery in Russia suggests otherwise.

In the Jan. 9 Nature, a team of British and Russian scientists describes the petrified remnants of a vent community that thrived during Earth's Silurian period, which ran from 438 million to 410 million years ago. Found in the southern Ural mountains, this deposit contains the oldest and most diverse set of fossil vent creatures ever discovered, report Crispin T. S. Little of the Natural History Museum in London and his colleagues.

Some denizens of the Silurian seafloor community are familiar, such as the large tubeworms seen at modern vents. Other members of the ancient oasis are unique, however. The Russian deposit includes fossilized brachiopods-clamlike creatures that do not populate any known vents today.

During the Silurian, brachiopods were abundant in the oceans, but they suffered severely during the mass extinction at the end of the Permian period, 250 million years ago. Their absence from modern vents indicates that these ocean bottom communities have not served as protective refuges, contend Little and his colleagues.