Traquairaspidiformes is an

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of extinct heterostracan

agnatha Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfish ...

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known from the

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and Early Devonian periods. Fossils are predominantly known from Late Silurian

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deposits from

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and

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: some species were also found in strata representing

shallow water marine environment Shallow water marine environment refers to the neritic marine environment between the shore and the shelf break. This environment is characterized by oceanic, geological and biological conditions, as described below, and water in this environmen ...

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and

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The head-shield and body armor of most traquairaspids form an almond shape. Plates have a distinctive ornamentation of tubercles: this ornamentation is very similar to the plate ornamentation of the heterostracan '' Weigeltaspis''. This similarity of ornamentation creates much confusion over the taxonomical placement of ''Weigeltaspis'', in addition to confusion over whether or not an isolated plate is of ''Traquairaspis'', or of ''Weigeltaspis''. Intact specimens of ''Weigeltaspis'' suggest a living animal similar to psammosteids like '' Drepanaspis''.Tarlo, Halstead. "LB t1965) Psammosteiformes tAgnatha)—A review with descriptions of new material from the Lower Devonian of Poland, II. Systematic Part." Palaeontologia Polonica 15: 168. Pages 20-21 The armor of ''Phialaspis symmondsi'' (once considered as species of ''Traquairaspis'') is shaped like a jet plane or paper airplane, with pointed wing-like crests and a dorsal crest near the posterior end of the armor. The body of "Yukonaspis," ''Traquairaspis angusta'', is greatly elongated, based on the holotype, a ventral plate. Most species of traquairaspids are placed within the type genus '' Traquairaspis''; most of the other genera, such as ''Phialaspis'', ''Toombsaspis'', and "Yukonaspis," have been synonymized into ''Traquairaspis''. ''Weigeltaspis'' is sometimes placed within Traquairaspidiformes on account of the plate ornamentation being almost identical to that of ''Traquairaspis''.

Taxonomy

* Family Phialaspididae White 1946 ** Genus '' Munchoaspis'' Tarrant 1991 ** Genus '' Phialaspis'' Wills 1935 ** Genus '' Toombsaspis'' Tarrant 1991 * Family Traquairaspididae Kiær 1932 corrig. ** Genus '' Pseudotraquairaspis'' Broad 1968 ** Genus '' Rimasventeraspis'' Tarrant 1991 'Yukonaspis'' Obručhev 1964 non Kobayashi 1936 non Stensiö 1964** Genus '' Traquairaspis'' Kiær 1932 'Orthaspis'' Brotzen 1934; ''Lophaspis'' Brotzen 1934 non Redtenbacher 1895; ''Lophaspiscis'' Whitley 1951* ?Family Weigeltaspididae Brotzen 1933/Tarlo 1962 ** ?Genus '' Weigeltaspis'' Brotzen 1933

References

{{Taxonbar, from=Q20683351 Heterostraci Prehistoric jawless fish orders Devonian jawless fish Silurian jawless fish Silurian first appearances Pridoli taxonomic orders Early Devonian taxonomic orders Early Devonian extinctions