A new ecological-severity ranking of major Phanerozoic biodiversity crises McGhee, George R., Jr. ; Clapham, Matthew E. ; Sheehan, Peter M. ; Bottjer, David J. ; Droser, Mary L. Abstract Publication: Palaeogeography Palaeoclimatology Palaeoecology Pub Date: January 2013 DOI: 10.1016/j.palaeo.2012.12.019 Bibcode: 2013PPP...370..260M