Middle Cambrian

The Middle Cambrian (also known as Albertan, Acadian, St. David's, or Saint David's) is the second of three geological epochs of the Cambrian period. It spans the time between 513 ± 2 Ma and 501 ± 2 Ma (million years ago). The strange organisms of the Burgess Shale fossil site lived during this epoch. The Middle Cambrian is divided into two unnamed ICS stages.