Consistently cool water environments within the tropics/subtropics: Carboniferous and Permian of Western Pangaea shelves

Larger benthic foraminifera and planktonic foraminifera with algal endosymbionts are particularly characteristic of warm, shallow waters and typically responded dramatically to environmental changes. Temperature is the most important physical factor that determines geographic distribution and affects the depth distribution of larger foraminifera by the development of a shallow thermocline that truncates the distribution of shallower species and excludes species adapted to the deepest euphotic zone. Temperature restricts larger foraminifera to those geographical regions or water depths characterized by temperatures never falling below 14 °C for several weeks. Three major biogeographic realms are recognized in the distribution of the Late Paleozoic foraminifers: Midcontinent-Andean (M-A), Boreal (B) and Tethyan (T). It has been seen long ago that taxonomic diversity in the M-A realm through Late Paleozoic was relatively low compare to T and B realms. The number of common genera in Mississippian and Pennsylvanian (Rheic pathway open) among all realms is quite high. However, M-A realm exhibiting two-three times lower diversity than in the T and B realms. The origin of genera mostly takes place in the T and in B realms. These genera then dispersed in North America where they are developed at the species level but diversity there was always twice or more as low as in B and T realms. Some cooler water taxa that mostly occur in northern and southern temperate zones are also known to appear in North American realm. Recent tropical larger foraminifera live within the depth of 0-150 m and optimal water temperature 30-20 ºC. The suggested favorable depth for fusulinids in B realm subtropics is 5-70m. The habitat of fusulinids in North American realm was much shallow (nearly three times) most probably due to cooler water conditions. The average temperature in the North American tropical shelves at the depth 0-10m was 15-20 ºC.