Protoconodonts are an extinct group of Cambrian animals known from fossilized

phosphatic Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphor ...

tooth-like structures. They were originally described as an informal group of early

conodonts Conodonts, are an extinct group of marine jawless vertebrates belonging to the Class (biology), class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning "cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known ...

, though more recent studies consider them to be more closely related to

chaetognaths The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, they are mostly pelagic; however about 20% of the known species ...

(arrow worms). Protoconodont elements are slender and pointed, with a hollow interior which opens towards the base of the structure. They develop entirely by the addition of layers to the inner cavity, extending the rim of the base. There is no additional mineralization on the outer surface, in contrast to paraconodonts or euconodonts (true conodonts). Protoconodont elements are frequently found bundled together into a 'superteeth', paired claw-like clusters which may have had a grasping function. These 'superteeth' were previously known by the name ''"Prooneotodus" tenuis'', now classified as a species of '' Phakelodus''.'''' A few protoconodont genera were previously assigned to the class Conodonta and the order Paraconodontida, and the genus '' Amphigeisina'' was even given its own superfamily, Amphigeisinacea. Protoconodonts were assumed to have been forerunners to paraconodonts, and by extension euconodonts. It is now thought that protoconodont elements (e.g., ''

Protohertzina ''Protohertzina'' is a genus of conodonts (protoconodonts or paraconodonts) or, possibly, Chaetognaths, found at the beginning of the Cambrian explosion. Protoconodonts are an extinct taxonomic group of conodonts.Zooproblematica and mollusca ...

anabarica'' Missarzhevsky, 1973), are probably grasping jaw spines of

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

chaetognaths rather than the oropharyngeal (mouth or throat) elements of paraconodonts or true conodonts. The jaw spines of '' Sagitta maxima'', a modern chaetognath, are practically identical to the fossils of ''Phakelodus tenuis'' in nearly every respect: shape, position, co-occurrence with smaller jaw spicules, and the presence of a sheath-like covering to protect the spines when not in use. This even extends to their three-layered internal microstructure, with a fibrous middle layer and a compatible array of trace elements. Although chaetognath jaws are fully organic (rather than phosphatic), this was likely true of protoconodonts as well, with mineralization only occurring after death due to

diagenetic Diagenesis () is the process of physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a role as sedi ...

alteration. In light of their taxonomic distinction from paraconodonts and euconodonts, protoconodonts were given their own formal order in 1995: Protoconodontida.

List of genera

* '' Amphigeisina'' (Bengtson, 1976) * '' Ganloudina'' He, 1983 * '' Gapparodus'' Abaimova, 1978 * '' Glauderia?'' Poulsen, 1967 * '' Gumella'' Müller & Hinz, 1991 * '' Hagionella'' Xie, 1990 * ''

Hertzina ''Hertzina'' is an extinct genus of conodonts in the family Furnishinidae. Fossils can be found in the Wheeler Shale Cambrian (c. 507 Mya) fossil locality in Utah, United States.Oldest Conodonts in North America. David L. Clark and Richard A. Ro ...

'' Müller, 1959 * '' Huayuanodontus''? (Dong, 1993) * '' Kijacus?'' Missarzhevsky and Mambetov, 1981 * ''

Mongolodus ''Mongolodus'' is an extinct genus of protoconodonts. References * * External links

* * Conodont genera Cambrian conodonts Paleozoic life of Newfoundland and Labrador Fossil taxa described in 1977 Chaetognatha Cambrian genus ex ...

'' Missarzhevsky, 1977 * '' Paibiconus''? Dong, 1993 * '' Phakelodus'' Miller, 1984 * ''

'' Missarzhevsky, 1973

References

* Middle and Upper Cambrian Protoconodonts and Paraconodonts from Hunan, South China. Dong Xi-Ping and Stig M. Bergström, Palaeontology, September 2001, Volume 44, Issue 5, pages 949–985, * On the evolution and histology of some Cambrian protoconodonts, paraconodonts and primitive euconodonts. Dong Xiping, Science in China Series D: Earth Sciences, July 2004, Volume 47, Issue 7, pages 577–584, * Ion microprobe U–Pb dating and Sr isotope measurement of a protoconodont. Yuji Sano, Kosaku Toyoshima, Akizumi Ishida, Kotaro Shirai, Naoto Takahata, Tomohiko Sato and Tsuyoshi Komiya, Journal of Asian Earth Sciences, Volume 92, 1 October 2014, Pages 10–17,

External links

* * Conodont taxonomy Cambrian conodonts Enigmatic prehistoric animal taxa Chaetognatha {{conodont-stub