The Permian–Triassic mass extinction forces the radiation of the modern marine phytoplankton

Medlin L.K. 2011. The Permian–Triassic mass extinction forces the radiation of the modern marine phytoplankton. Phycologia 50: 684–693. DOI: 10.2216/10-31.1 Among modern eukaryotic marine phytoplanktonic lineages possessing red algal plastids are the diatoms, dinoflagellates and haptophytes including coccolithophorids. Although origins of these host lineages and the timing of the endosymbioses leading to their ability to photosynthesize are ancient, their modern radiations are not. Molecular clocks suggest the timing of the origins and the radiations of these host lineages are different among the three groups. Dinoflagellates and haptophytes had class and order level radiations from 500 to 600 megaannum (Ma) and genus-level radiations, especially among the thecate dinoflagellates, about 250 Ma. Pigmented heterokonts, the last divergence in the heterokont tree, originated between 770 and 1000 Ma, but most planktonic unicellular groups diverged at the Permian–Triassic (P/T) boundary (250 Ma) and radiated th...