Taphonomy and palaeoecology of a Late Ordovician caryocaridid from the Soom Shale Lagerstätte, South Africa

Abstract

A new species of caryocaridid is reported from the Late Ordovician of South Africa. The fossils show a complex, multi-layered structure that may represent exceptional preservation of the original arthropod exo-, endo- and epicuticle. Alternatively, the layered structure may comprise the carapace, with a mineralized cast of the internal void and a layer of fibrous illite external to the carapace. The genesis of the fibrous illite is important as it demonstrates that not all fibrous textures associated with fossils in the Soom Shale, and perhaps other Lagerstätten, can be interpreted as mineralized muscle tissue. Caryocaris cedarbergensis n.sp. extends the geographical, ecological and temporal range of the family and provides the first evidence of a zooplanktonic constituent to the Soom Shale biota. The genus most likely represents a cool-adapted mesopelagic group during the Early–Middle Ordovician, which inhabited an epipelagic cold-water shelf environment during the Late Ordovician.