Anomalocaridid appendage

Early Ordovician

Upper Fezouata Formation

Zagora, Morocco.

29mm appendage on 56mm slab.  Exceedingly rare in the Ordovician.

Anomalocarid.  Arthropod.

Anomalocaridids are a group of actively-swimming arthropods (Suborder Anomalocaridida) best known from the Cambrian but surviving into the Devonian.  In the Cambrian they were the largest predators on earth at about 3 feet in length.  In the Ordovician one form was twice the size but had evolved into a filter-feeder.  Only some nautiloids of the time were larger.

Once thought to have died out by the end of the Cambrian, an anomalocaridid was described from the Early Devonian of Germany (Hunsruck Shale) in 2009.