A scolecodont is the jaw of a

polychaete Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ma ...

annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecolo ...

, a common type of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

-producing

segmented worm The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecolog ...

useful in

invertebrate paleontology Invertebrate paleontology (also spelled invertebrate palaeontology) is sometimes described as invertebrate paleozoology or invertebrate paleobiology. Whether it is considered to be a subfield of paleontology, paleozoology, or paleobiology, this d ...

. Scolecodonts are common and diverse

microfossil A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

s, which range from the

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ( ...

period (around half a billion years ago at the start of the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and '' ...

era) to the

present The present (or here'' and ''now) is the time that is associated with the events perceived directly and in the first time, not as a recollection (perceived more than once) or a speculation (predicted, hypothesis, uncertain). It is a period of ...

. They diversified profusely in the Ordovician, and are most common in the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

and

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

marine deposits of the

era. Relatedly, more problematic

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

-like

s have been described in even older,

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is pre ...

era deposits in the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

Hills of southern Australia and in mid-

deposits of

Burgess shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

in British Columbia. Since the other classes of annelids (specifically, the

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...

s and

leech Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodie ...

es) lack hard parts, only the sea-dwelling polychaetes are frequently represented in the

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

. Polychaetes are commonly

ized due to their chitinous teeth and their dwelling tubes made of durable

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

(a calcium carbonate), hardened

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

(a.k.a. parchment), and/or chitin-like cement.

Taxonomy

Scolecodonts belonging to the

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

families Atraktoprionidae, Hadoprionidae, Kalloprionidae, Mochtyellidae, Paulinitidae, Polychaetaspidae, Ramphoprionidae, Rhytiprionidae, Skalenoprionidae, Symmetroprionidae, Xanioprionidae, and the still-

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extin ...

(living) family Oenonidae (which includes the Arabellidae) are known from

rocks in Scotland. Scolecodonts representing the present-day families

Onuphidae The Onuphidae are a family of polychaete worms. Characteristics Most onuphids have tubes. Some live semisubmerged in the substrate, but others carry their tubes around, and they can all rebuild their tubes if necessary. The tubes, thin and parch ...

and Dorvilleidae first appeared in

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

era deposits.

History

Segments of the fossil jaw of a polychaete worm were first reported from Silurian strata on the Estonian island of

Saaremaa Saaremaa is the largest island in Estonia, measuring . The main island of Saare County, it is located in the Baltic Sea, south of Hiiumaa island and west of Muhu island, and belongs to the West Estonian Archipelago. The capital of the island i ...

in 1854, 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. 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''. Extensive studies in the late 19th century by George J. Hinde of material from England, Wales, Canada and SwedenHINDE, 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. established a basis for the nomenclature of what he regarded as isolated components of annelid jaws; but study of them lapsed thereafter for almost 50 years.

References

{{reflist

External links

scolecodonts.net
including complete scientific bibliography, lists of fossil genera and species, and selection of images
graptolite.net
Piotr Mierzejewski's page on microfossils Annelids Fossil record of animals Microfossils