Fossil sphenopsid, Annularia Stellata- by sysadmin | Jan 7, 2016 | Blog | 0 comments Fossil sphenopsid, Annularia Stellata- Pennsylvanian deposits. Mazon Creek locality, Francis Creek Shale, Coal City, Illinois. Pennsylvanian period 300 mya. 6″ across Annularia are the leaf whorls of an extinct horsetail, Calamites.