Problematic urn-shaped fossils from a Paleoproterozoic (2.2Ga) paleosol in South Africa Retallack, Gregory J. ; Krull, Evelyn S. ; Thackray, Glenn D. ; Parkinson, Dula Abstract Publication: Precambrian Research Pub Date: September 2013 DOI: 10.1016/j.precamres.2013.05.015 Bibcode: 2013PreR..235...71R