Eryonidae

Eryonidae is a family of fossil decapod crustaceans which lived from the Upper Triassic to the Lower Cretaceous. It contains four genera: An aggregation of three unidentified eryonids was reported in 2012 inside a Late Jurassic ammonoid of the species "Harpoceras falciferum"; they represent the earliest evidence of gregarious behaviour in decapods.