THE EVOLUTION OF RADIOLARIAN BIODIVERSITY

Abstract

Radiolarians are protozoans that have existed for more than 500 million years. Paleozoic radiolarians (dating from 550-250 million years ago) were represented by three orders, 16 families, and 76 genera. Eighty per cent of Paleozoic radiolarians did not survive beyond the Paleozoic-Mesozoic boundary. Mesozoic Radiolaria (245-65 million years ago) were represented by three orders (two of which continued from the Paleozoic and one that appeared in the Mesozoic), 49 families, and 256 genera. The total number of known Cenozoic and recent Radiolaria is almost 5000 species. Analysis of radiolarian biodiversity over time reveals a trend toward decreasing numbers of the order Nasselaria contrasting with relatively stable or even increasing number of Spumellaria.