Silica Use Through Time: Macroevolutionary Change in the Morphology of the Diatom Fustule

Diatoms have evolved an obligate requirement for silica for their ornamented cell wall. Diatom productivity and subsequent burial of their siliceous remains on the ocean floor is a major control on the marine silica cycle. The ecological success of the diatoms over the Mesozoic and Cenozoic is associated with biogeographic shifts in siliceous sponges, decreasing silicification in the radiolarians, and a global decrease in oceanic silicic acid concentrations. We review what is known about the evolutionary advantages of the silica frustule and how selection pressures, including decreasing silicic acid concentrations, changes in growth limiting nutrients other than Si, CO2, irradiance, predation and viral pressures have shaped the morphology of the frustule over the Mesozoic and Cenozoic.