Radiolarian diversity patterns in the latest Jurassic–earliest Cretaceous

The global diversity patterns of latest Jurassic–earliest Cretaceous (Tithonian–Berriasian) radiolarian faunas were analyzed based on samples from the European Alps, Oman, Philippines and Antarctica and an extensive literature survey. Several measures of diversity were applied to faunas from tropical (Oman, Mexico, Pacific), subtropical (Alps, California, Philippines, Japan), and subpolar (Antarctic Peninsula, New Zealand, Northern Russia) localities. Original diversity patterns are obscured by taxonomic, sedimentological, and preservational biases. Qualitative and quantitative corrections of these biases indicated a significant diversity gradient from tropical–subtropical to subpolar latitudes, but no significant difference between tropical and subtropical assemblages. The latitudinal diversity gradient was apparently asymmetrical, being steeper in the Northern Hemisphere than in the Southern Hemisphere. In the Southern Hemisphere the diversity gradient was similar to the one observed in modern radiolarian sedimentary assemblages. Considering the more equable climate of the Tithonian–Berriasian, it appears unlikely that temperature was the only control of the observed diversity patterns. The results substantiate the notion of latitudinal diversity gradients as a time-invariant feature of the Earth, possibly driven by gradients in biome size.