An extinct order of arthropods that were one of the first complex creatures on Earth. The first ones date back over 530 million years but they were all wiped out before the Dinosaurs around 220 million years ago. Completely aquatic and very diverse, the smallest were just a few millimeters long, the largest around 1.5 meteres.

Elrathia kingii

One of the oldest complex creatures on Earth dating to around 520 million years ago. From the Wheeler shale of Utah - USA they are from the Cambrian period.