Study Slab (IMAGE) University at Buffalo Caption A slab of rock from a study site in Nevada harbors many specimens of colonies of Metabolograptus extraordinarius, a shallow-water graptolite species, which together with some close relatives, replaced all the formerly dominant species following the end-Ordovician mass extinction Credit Credit: Charles E. Mitchell Usage Restrictions This image may only be used in conjunction with news stories discussing the research described in the associated press release. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.