The Lower Cambrian problematicum Spatangopsis costata Torell, 1870

Perhaps the most famous fossils from the Lower Cambrian Mickwitzia Sandstone of south-central Sweden are the sandy bodies known as Spatangopsis costata. Much of their fame rests on Nathorst’s (1881, 1910) classical interpretation of them as remains of medusae, including gastral fillings (steinkerns) and subumbrellar impressions. The mass occurrence of preserved jellyfish would be all the more notable in view of the otherwise great rarity of fossilized Cambrian medusae. Though it received considerable recognition, Nathorst’s interpretation is today considered unlikely (e.g. Scholz 1977), on both taphonomic and morphologic grounds. Outside Sweden, Spatangopsis is known only through a single specimen from the Lükati Sandstone of Estonia (Schmidt 1888). Correlation based on macrofossils place both the Mickwitzia and Lükati Sandstones in the Schmidtiellus mickwifzi Biozone (e.g. Bergström 1981), while correlation based on acritarchs indicate that the Mickwitzia Sandstone may belong to the younger Holmia inusitata Biozone (e.g. Moczydlowska 1991).