Early Ordovician (Arenigian)

Upper Fezouata Formation

Zagora, Morocco

20mm arthropod on 81mm x 135mm slab. Includes counterpart.

Arthropod.

Xiphosurine is a term referring to a member of the arthropod Order Xiphosura, the group that includes all horseshoe crabs and their close relatives, extinct and extant.  This group is more closely related to arachnids than crustaceans.

This specimen may represent the earliest-known form belonging to the Xiphosura – perhaps too primitive to call it a horseshoe crab.