Ptychagnostus praecurrens Burgess Shale Agnostid Trilobite

Description: When first discovered in Walcott’s quarry, this trilobite was named Triplagnostus buregessensis. It was later determined to be the same as an earlier agnostid named Ptychagnostus praecurrens. The members of the Agnostida are mostly thought to have been planktonic in nature. Most are blind, and have a pygidium equal in size to the cephalon (ispopygous), making it hard to tell which end was which! Order Agnostida comprises trilobites that appeared in the Lower Cambrian, became widespread and then declined to become rare in the Ordovician prior to their complete extinction by the end of the Ordovician. They are so unusual that some experts have suggested that one of the two suborders, Agnostina, should not even be included in Class Trilobita. It is remarkably detailed for such a tiny specimen, and fully articulated.