It seems like echinoderms became five-way symmetric incredibly quickly following the group’s first appearances in the early Cambrian. We don’t really know why this secondary radial symmetry evolved in the group – but we do know that the common ancestors of all modern pentaradial echinoderms were suspension-feeding animals that lived attached to the sea floor.
And those ancestors were probably a group called the edrioasteroids.
Continue reading “Cambrian Explosion Month #13: Phylum Echinodermata – Sticking Around”