When did echinoderms first appear in the fossil record?

Echinoderms first appeared in the fossil record at the beginning of the Cambrian Period, which occurred approximately 542 million to 488 million years ago.1

Because the phylum was already well-diversified by the Lower Cambrian, scientists believe that a significant amount of evolution must have taken place during the Precambrian. It is speculated that earlier echinoderms existed but lacked a calcite skeleton, which prevented them from being preserved in the fossil record. While some Precambrian fossils have been suggested as possible "pre-echinoderms," the clear, rich history of the group begins with the dawn of the Cambrian.21