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Phylogenetic nodes are labelled with letters U-X according to Fig. 1. The diversification of the Antarctic Clade (node X) coincides with an increase in frequency of glacial extensions well onto the shelf, the Mi-1 glacial event, the first occurences of sea-ice dependent diatoms in Antarctic waters, and a sharp decline of atmospheric CO2 levels. Paleoc.:Paleocene, Oligoc.:Oligocene, Pl.:Pliocene, P.:Pleistocene.
