The examination of radiolarian biodiversity at the family level through
Phanerozoic time reveals some general trends known in other groups of
organisms, especially among plankton, while some other trends seem to be
quite peculiar. The Permian/Triassic crisis that is one of the most
important in the evolution of marine organisms, is marked in radiolarian
assemblages by the extinction of two orders (Albaillellaria and
Latentifistularia) towards the end of the Permian, and mostly by the
tremendous diversification of Spumellaria and Nassellaria in the
early-mid Triassic. Radiolarian diversity increased from Cambrian to
Jurassic, remained quite stable during the Cretaceous and has decreased
slightly since then.