SILURIAN HYDROTHERMAL-VENT COMMUNITY FROM THE SOUTHERN URALS, RUSSIA

MODERN hydrothermal-vent communities are remarkable for being dependen t on bacterial chemosynthetic primary production and for having a high percentage of endemic taxa (95% at the species level)(1-3). Based on phylogenetic analyses, it has been suggested that some of these taxa a re Mesozoic or even Palaeozoic relicts, and that the vent environment has thus acted as a refuge against evolutionary pressures, such as rna s extinctions, that affect other ecosystems(1,2,4). However, little is known about ancient vent communities because fossils have been report ed from very few(5-11) of a thousand or so documented vent deposits(12 ). Here we describe a macrofossil assemblage of monoplacophoran mollus cs, inarticulate brachiopods, vestimentiferan tube-worms and other tub es, probably of polychaete origin, from the Silurian Yaman Kasy deposi t(12). The assemblage represents the oldest, and most diverse, fossil hydrothermal-vent community known, and shares vestimentiferan and poly chaete tube-worms with both modern vent communities(1,2) and other anc ient vent assemblages(7-12), but is unique in baring brachiopods and m onoplacophorans. Modern rant communities are not refuges for these Sil urian shelly vent taxa, a finding that may have implications for the r efuge hypothesis.