Ptychagnostus atavus

Ptychagnostus atavus Temporal range: Drumian PreЄ Є O S D C P T J K Pg N ↓
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	†Trilobita
Order:	†Agnostida
Family:	†Ptychagnostidae
Genus:	†Ptychagnostus
Species:	†P. atavus
Binomial name
Ptychagnostus atavus (Tullberg (), 1880)
Synonyms
Acidusus atavus (Tullberg, 1880) Agnostus atavus Tullberg 1880

Ptychagnostus atavus is a species of agnostid trilobite. It belongs to the genus Ptychagnostus in the family Ptychagnostidae. 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 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 Cambrian Series 3 (Middle Cambrian).