Silurian hydrothermal-vent community from the southern Urals, Russia

Abstract

MODERN hydrothermal-vent communities are remarkable for being dependent 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 are Mesozoic or even Palaeozoic relicts, and that the vent environment has thus acted as a refuge against evolutionary pressures, such as mass extinctions, that affect other ecosystems^1,2,4. However, little is known about ancient vent communities because fossils have been reported from very few^5–11 of a thousand or so documented vent deposits¹². Here we describe a macrofossil assemblage of monoplacophoran molluscs, inarticulate brachiopods, vestimentiferan tube-worms and other tubes, probably of polychaete origin, from the Silurian Yaman Kasy deposit¹². The assemblage represents the oldest, and most diverse, fossil hydrothermal-vent community known, and shares vestimentiferan and polychaete tube-worms with both modern vent communities^1,2 and other ancient vent assemblages^7–12, but is unique in having brachiopods and monoplaco-phorans. Modern vent communities are not refuges for these Silurian shelly vent taxa, a finding that may have implications for the refuge hypothesis.