Scolecodonts
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A scolecodont is the jaw of a polychaete annelid, a common type of fossil-producing segmented worm. Scolecodonts are common and diverse microfossils and trace fossils, which range from the Cambrian period (around half a billion years ago at the start of the Paleozoic era) to the present. However, scolecodonts are reported most commonly from Ordovician, Silurian and Devonian marine deposits of the Paleozoic era.
Relatedly, more problematic worm-related 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.
Scolecodonts beonging to the extinct families Atraktoprionidae, Hadoprionidae, Kalloprionidae, Mochtyellidae, Paulinitidae, Polychaetaspidae, Ramphoprionidae, Rhytiprionidae, Skalenoprionidae, Symmetroprionidae, Xanioprionidae, and the still extant family Oenonidae (which includes the Arabellidae) are known from Silurian rocks in Scotland. In addition, scolecodonts represnting the modern families Onuphidae and Dorvilleidae first appear in Mesozoic deposits. All of these are errant polychaetes.
Common genera of scolecodonts, both extant and extinct (the latter labelled †), are:
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- Serpula (Silurian period to present, found worldwide)
- Spirorbus (Ordovician period to present, found throughout North America)
- †Glomerula (early Jurassic period to the Paleocene epoch, found worldwide)
- †Hamulus (Cretaceous period only, found along east coast of North America)
- †Proliserpula (late Cretaceous period only, found throughout Europe)
- †Rotularia (late Cretaceous period to the Eocene epoch, found throughout North America and Europe)
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