Visaggi, Christy ('01)   (Advisor: Connie Soja)

    Upper Silurian stromatolite reefs in the Ural Mountains of Russia contain a problematic hydroid, Fistulella, originally described by V.P. Shuysky (1970). They are preserved in association with a moderate diversity of crinoids, brachiopods, ostracodes, aphrosalpingid sponges, and calcified microbes. Fossils similar in appearance to Fistulella occur in stromatolite boundstones of comparable age in the Alexander terrane of Alaska. An examination of specimens from the Ilych River in the Northern Urals and Glacier Bay National Park of Alaska was undertaken to determine if they belong to Fistulella and exhibit hydroid anatomy and lifestyles.

    Burial experiments were used to assess hydroid taphonomy by studying the early stages in soft-body preservation of modern hydroids similar in morphology to Fistulella. These experiments confirm that most hydroids are unlikely to be preserved in the fossil record and that Fistulella probably contained a chitinous hydrocaulus. Thin section analysis suggests the fossils from Alaska and Russia can be identified as Fistulella undosa Shuysky, 1973, on the basis of the simple, tubular shape of the undeformed polyps with an average diameter of 2-3 mm and an average length of 5-7 mm. These problematic organisms exhibit poorly preserved walls defined by microbial (or sponge) encrustations, rare branching, and recrystallized interiors.

    The location of Fistulella in Russia and Alaska adds new data to paleogeographic reconstructions for a shared Uralian seaway between the paleocontinents of Laurentia, Baltica, and Siberia. Fistulella remains a problematic hydroid due to its poor preservation and lack of close analogy with modern hydroids, however its presence in the exotic Alexander terrane and Russia confirms that shallow marine fauna were able to transmigrate between the two locations, thus providing additional evidence to support the placement of Alaska's Alexander terrane along the Late Silurian seaway.

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