| Ptychagnostus atavus Temporal range:
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Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | †Trilobita (?) |
| Order: | †Agnostida |
| Family: | †Ptychagnostidae |
| Genus: | †Ptychagnostus |
| Species: | †P. atavus
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| Binomial name | |
| †Ptychagnostus atavus (Sven Axel Tullberg, 1880)
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| Synonyms | |
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Ptychagnostus atavus is a species of agnostid trilobite. It was originally described by Swedish paleontologist Sven Axel Tullberg as Agnostus atavus in 1880.[1] It is used in biostratigraphy as an index fossil. Its first appearance at the GSSP section in the Wheeler Shale of Utah is defined as the beginning of the Drumian Age (around 504.5 million years ago) of the Miaolingian (Middle Cambrian).[2][3]
Laurie (2008) [4] grouped punctuosus and affinis within Ptychagnostus, but preferred to place the closely related atavus within Acidusus.
- ^ "Ptychagnostus atavus". Paleobiology Database. Retrieved 16 November 2012.
- ^ Babcock, L. E.; Robison, R. A.; Rees, M. N.; Peng, S.; Saltzman, M. R. (2007). "The Global boundary Stratotype Section and Point (GSSP) of the Drumian Stage (Cambrian) in the Drum Mountains, Utah, USA" (PDF). Episodes. 30 (2): 85–95. doi:10.18814/epiiugs/2007/v30i2/003.
- ^ Ogg, G. "GSSP for Drumian Stage". Geologic TimeScale Foundation. Retrieved 16 November 2012.
- ^ LAURIE J. R. 2008. Species relationships in the Ptychagnostidae (Cambrian, Agnostina). In: Ra´bano I., Gozalo R. & GarciaBellido D. eds. Advances in trilobite research, pp. 211–218. Cuadernos del Museo Geominero 9.