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Scolecodont
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, 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.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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