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Scolecodont

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An Ordovician scolecodont from Estonia

A scolecodont is the jaw of a polychaete annelid, a common type of fossil-producing segmented worm useful in invertebrate paleontology. Scolecodonts are common and diverse microfossils, which range from the Cambrian period (around half a billion years ago at the start of the Paleozoic era) to the present. They diversified profusely in the Ordovician,[1] and are most common in the Ordovician, Silurian and Devonian marine deposits of the Paleozoic era.

Relatedly, more problematic worm-like fossils have been described in even older, Neoproterozoic era deposits in the Ediacaran Hills of southern Australia and in mid-Cambrian deposits of Burgess shale in British Columbia.

Since the other classes of annelids (specifically, the earthworms and leeches) lack hard parts, only the sea-dwelling polychaetes are frequently represented in the fossil record. Polychaetes are commonly fossilized due to their chitinous teeth and their dwelling tubes made of durable calcite (a calcium carbonate), hardened mucus (a.k.a. parchment), and/or chitin-like cement.

Taxonomy

Scolecodonts belonging to the extinct families Atraktoprionidae, Hadoprionidae, Kalloprionidae, Mochtyellidae, Paulinitidae, Polychaetaspidae, Ramphoprionidae, Rhytiprionidae, Skalenoprionidae, Symmetroprionidae, Xanioprionidae, and the still-extant (living) family Oenonidae (which includes the Arabellidae) are known from Silurian rocks in Scotland. Scolecodonts representing the present-day families Onuphidae and Dorvilleidae first appeared in Mesozoic era deposits.

History

Segments of the fossil jaw of a polychaete worm were first reported, from Silurian strata on the Estonian island of Saaremaa, by Eduard Eichwald ,[2] but they were misinterpreted as fish teeth. A year later, impressions of whole polychaete worms with poorly preserved jaws were described from Italian Tertiary deposits by Abramo Massalongo.[3] Subsequently E. Ehlers, a specialist on recent polychaetes, recorded them from the Jurassic Solenhofen Stone of Bavaria, Germany, demonstrating their affinity and proposing the generic names Eunicites and Lumbriconereites.[4][5] Extensive studies by George J. Hinde of material from England, Wales, Canada and Sweden [6][7][8][9] established a basis for the nomenclature of what he regarded as being isolated components of annelid jaws; but study of them lapsed thereafter for almost 50 years.

References

  1. ^ Hints, O.; Eriksson, M. (2007). "Diversification and biogeography of scolecodont-bearing polychaetes in the Ordovician". Palaeogeography, Palaeoclimatology, Palaeoecology. 245: 95. doi:10.1016/j.palaeo.2006.02.029.
  2. ^ EICHWALD, E. 1854. Die Grauwackenschichten von Lieu-und Esthland. Bulletin de la Societe Imperiale des Naturalistes de Moscou, 27, 1-111.
  3. ^ MASSALONGO, A. 1855. Monografica delle Nereidi fossili del Monte Bolca. Antonelli, Verona, 55 pp.
  4. ^ EHLERS, E. 1868a. 12Iber eine fossile Funicee aus Solenhofen (Eunicites aritus), nebst Bemerkungenvtiber fossile Wtirmer tiberhaupt. Zeitschrifl ftir wissenschaftliche Zoologie, 18, 421-443.
  5. ^ EHLERS, E. 1868b. Ueber fossiler Wtirmer aus dem lithographischen Schiefer in Bayern. Palaeontographics, 17, 145-175.
  6. ^ HINDE, G. J. 1879. On annelid jaws from the Cambro-Silurian, Silurian and Devonian Formations in Canada and from the Lower Carboniferous in Scotland. Quarterly Journal of the Geological Society of London, 35, 370-389.
  7. ^ HINDE, G. J. 1880. On annelid jaws from the Wenlock and Ludlow Formations of the west of England. Quarterly Journal of the Geological Society of London, 36, 368-378.
  8. ^ HINDE, G. J. 1882. On annelid remains from the Silurian strata of the Isle of Gotland. Birand till Kungliga Svensk Vetenskapsakademiens, Hindlingas, 7, 3-28.
  9. ^ HINDE, G. J. 1896. On the jaw-apparatus of an annelid (Eunicites reidiae sp. nov.) from the Lower Carboniferous of Halkin Mountain, Flintshire. Quarterly Journal of the Geological Society of London, 52, 438-450.
  • scolecodonts.net including complete scientific bibliography, lists of fossil genera and species, and selection of images
  • graptolite.net Piotr Mierzejewski's page on microfossils
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