Ptychagnostidae

Ptychagnostidae is a family of agnostid trilobites from the 5th Stage to the Paibian Age of the Cambrian (509 to 497 million years ago). The family includes several important index fossils. Like all agnostids, ptychagnostids have cephalons and pygidia that are more or less uniform in size and shape (isopygous). The thorax is composed of two body segments (somites). They are completely blind. Ptychagnostidae has a cosmopolitan distribution. They existed during the 5th Stage of the Series 3 Epoch to the Paibian Age of the early Furongian Epoch in the Cambrian (509 to 497 million years ago). The earliest member of the family is Ptychagnostus praecurrens from the Burgess Shale fauna. Ptychagnostidae is classified under the superfamily Agnostoidea of the suborder Agnostina, order Agnostida. The family was first established by the Japanese paleontologist Teiichi Kobayashi in 1939. Its name comes from the type genus, Ptychagnostus, which is itself derived from Ancient Greek πτυχος (ptychos, 'folded') and άγνωστος (ágnostos, 'unknown'). It includes the following genera (with their taxonomic synonyms):