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Mystery Fossil 7


Fossil 7From Newsletter 58:

    Mystery Fossil Seven was found recently by post-graduate students in a thin section of beach rock from the Bahamas in the Leeds University Earth Sciences teaching collection. The fossil appears to be formed of calcium carbonate and is round and cog-like with eleven “spokes”. It is approximately 400 microns in diameter. The host beach rock sediment may only be a few hundreds of years old. Ideas as to its origin include calcareous green algae or holothurian plates.

    Answers in an email (or, if the traditionalists prefer: on a postcard, scanned and attached to an email) to Cris Little.
Developments from Newsletter 59:
    Mystery Fossil Number Seven has attracted a small flurry of e-mail activity. John Hampton at Edinburgh identified it as a very nearly horizontal section of a holothurian wheel sclerite, while Steve Donovan at the Nationaal Natuurhistorisch Museum, Leiden identified it as two fossils, with the spoked centre being a transverse section through an echinoid spine, most probably from a diadematoid, and the surrounding outer ‘vesicular’ structure being a possible algal coating on the spine. A third party was called in to adjudicate (David Pawson at the Smithsonian) and he sided with Steve’s identification. David states that the fossil is not a holothurian ossicle, firstly because it seems to have an unadorned central cavity, secondly because the rim area (with or without algae) is unlike holothurian wheels. Finally, present-day holothurians with 11-spoked wheels (Family Myriotrochidae) live mostly in bathyal/abyssal depths in the central Atlantic region; in the Arctic, one or two species venture into shallower depths. Perhaps three western Atlantic shallow-water species have wheel ossicles, and in these all of the wheels have six spokes. Echinoderms seem to be quite popular!



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