Setapedites abundantis Lustri, Gueriau & Daley, 2024
Early Ordovician (Arenigian)
Upper Fezouata Formation
Zagora, Draa Valley, Morocco

111mm slab with 5 aglaspids, each about 7mm. One is complete and shows some appendages, others are partials

Described for the first time in May 2024, this is perhaps the earliest known occurrence of synziphosurines which are better known from the Early Silurian to Early Carboniferous. A synziphosurine is a member of a suborder of arthropods, Synziphosurina, considered to be stem-group xiphosurans. In other words, based on current understanding, they may not be ancestral to xiphosurans (horseshoe crabs) but they are more closely related to their ancestors than to other groups.

Video is an amazing 3D scan of a similar specimen from the Silurian

A nice summary of the new research can be found here: Surprise Discovery Reveals Earliest Known Ancestor of Scorpions And Spiders

Read the original scientific paper here: Lower Ordovician synziphosurine reveals early euchelicerate diversity and evolution (opens in new tab)