''Ptychagnostus'' is a member of the
agnostida
Agnostida is an order of arthropod which have classically been seen as a group of highly modified trilobites, though some recent research has doubted this placement. Regardless, they appear to be close relatives as part of the Artiopoda. They a ...
that lived during the
Cambrian
The Cambrian Period ( ; sometimes symbolized C with bar, 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 ...
period. Ptychagnostidae generally do not exceed one centimetre in length.
Their remains are rarely found in empty tubes of the polychaete worm ''
Selkirkia
''Selkirkia'' is a genus of predatory, tubicolous priapulid worms known from the Middle Cambrian Burgess Shale, Ogygopsis Shale and Puncoviscana Formation. 142 specimens of ''Selkirkia'' are known from the Greater Phyllopod bed, where they compr ...
''. The genus probably ranged throughout the water column. It has two glabellar lobes, and three pygidial lobes.
Type species
''Agnostus punctuosus'' Angelin, 1851 from the ''Pt. punctuosus'' Zone of the Alum Shale (
Drumian
The Drumian is a stage of the Miaolingian Series of the Cambrian. It succeeds the Wuliuan and precedes the Guzhangian. The base is defined as the first appearance of the trilobite ''Ptychagnostus atavus'' around million years ago. The top is def ...
), Sweden (by original designation). Official ruling on the conservation of accepted usage of ''A. punctuosus'' as the type species was given by the International Commission on Zoological Nomenclature, 1993.
Remarks
''Ptychagnostus affinis'' (Brøgger 1878) was once considered a subspecies of ''Pt. punctuosus''.
Laurie (2008) grouped ''punctuosus'' and ''affinis'' within ''Ptychagnostus'', but preferred to place the closely related ''atavus'' within ''Acidusus''.
Ptychagnostidae Genera
Høyberget & Bruton (2008)
[ HØYBERGET M. & BRUTON D. L. 2008. Middle Cambrian trilobites of the suborders Agnostina and Eodiscina from the Oslo Region, Norway. ''Palaeontographica'' A286, 1–87. ] concluded that the following genera belong in the Ptychagnostidae: ''Ptychagnostus, Goniagnostus, Tomagnostus, Lejopyge, Aotagnostus'' and ''Onymagnostus''.
Species
*''Ptychagnostus punctuosus'' (Type species).
*''Ptychagnostus affinis'' (formerly ''Pt. punctuosus affinis'')
*''Ptychagnostus aculeatus''
*''Ptychagnostus akanthodes''
*''
Ptychagnostus atavus
''Ptychagnostus atavus'' is a species of agnostid trilobite. It was originally described by Swedish paleontologist Sven Axel Tullberg as ''Agnostus atavus'' in 1880. It is used in biostratigraphy as an index fossil. Its first appearance at the G ...
''
*''Ptychagnostus cassis''
*''Ptychagnostus ciceroides''
*''Ptychagnostus cuyanus''
*''Ptychagnostus germanus''
*''Ptychagnostus gibbus''
*''Ptychagnostus hybridus''
*''Ptychagnostus intermedius''
*''Ptychagnostus michaeli''
*''Ptychagnostus praecurrens''
*''Ptychagnostus seminula''
References
External links
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Agnostida genera
Agnostoidea
Cambrian trilobites
Burgess Shale fossils
Wheeler Shale
Paleozoic life of New Brunswick
Paleozoic life of Newfoundland and Labrador
Drumian genera
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