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1 The Natural History Museum, Cromwell Road, London SW7 5BD, UK
2 Institute of Mineralogy, Urals Branch Russian Academy of Sciences, Miass, Chelyabinsk district 456301, Russia
There are 19 known fossiliferous volcanogenic massive sulphide (VMS) deposits which range in age from the Silurian to the Eocene. Most of these are in the Ural Mountains, Russia. The deposits contain assemblages of inarticulate and rhynchonellid brachiopods; gastropod, bivalve and monoplacophoran molluscs; and a small diversity of worm tube morphologies, some of which may be attributable to alvinellid polychaetes and vestimentiferans. The fossils are preserved mainly as external moulds of pyrite, which is consistent with biomineralization processes occurring at modern vent sites. Most of the fossil taxa are new to science, but the lack of original shells and organic tubes makes placement in existing phylogenetic schemes difficult. A comparison between modern vent communities and fossil vent assemblages shows that vestimentiferans, alvinellid polychaetes, bivalves, gastropods, monoplacophorans and perhaps brachiopods are shared at higher taxonomic levels, but that arthropods are found only in the modern communities. There are no direct ancestor-descendant relationships between the fossil and modern vent molluscs and brachiopods. This demonstrates that the modern vent environment is not a refuge for the known Palaeozoic and Mesozoic shelly vent taxa. Hence, taxonomic groups have moved in and out of the vent ecosystem through time. These findings are discussed in relation to alternative hypotheses for the origins of modern vent communities.
