Aegirocassis benmoulai
Early Ordovician
Fezouata Formation
Mecissi-Zagora Region, Draa Valley, Morocco
28mm anomalocaridid appendage on 90mm slab.

Arthropod.  Soft-bodied.

Aegirocassis is a genus of anomalocaridid known only from the Early Ordovician of Morocco.  It was one of the largest of all arthropods that ever lived, reaching about 6 1/2 feet long – almost certainly the largest animal of its time.  Like the largest animal of our time, the blue whale, it has been determined to have been a filter-feeder that descended from predatory ancestors.

Anomalocaridids were once thought to have died out by the end of the Cambrian but a new one was described from the Early Devonian of Germany in 2009.

Have a look at this amazing 3D model of Aegirocassis courtesy of Google and darwinmuseum.ru. Click on the arrows at the bottom right corner to see it full screen!