Analysis of Species Richness Dynamic of Mesozoic and Cenozoic Radiolarians

Abstract

In this article was studied dynamic of radiolarians species richness over the last 150 million years with accuracy up to the geological age. The basic regularities of species and taxa of the upper range changing are established for Mesozoic and Cenozoic eras. Changing of the species abundance on the borders of large geological periods and, also significant fluctuations of the species richness connect to a combination of the numerous factors. Most important of these are the geological processes leading to extensive transgressions and regressions, climate variations, general directed evolution of the Earth biota, and competition for important chemical components for radiolarians’ vital processes. The appearance of considerable areas of tropical forests on the land with their enormous productivity and biochemical weathering is connected to the late Cretaceous era. That led to increasing of the dissolved material flow to the sedimentation pool, that recorded by an appearance of classic bauxite. Because aluminum oxide and silicon oxide are geochemically bound, we can state also about increasing of dissolved silica in-flow caused by diatoms development, which became a competitors for radiolarians in the struggle for silica. The last ones are lost in that competition, what led to its species reduction. Mass extinction at the border between the Cretaceous and Paleocene was not a catastrophic event with instant extinction, but a lengthy process.