Recent radiolarian fauna living to the south of the Antarctic Polar Front is known to differ sharply from that living in the tropical regions of the Indo-Pacific. About 78 % of the total number of radiolarians in Antarctic bottom assemblage were unchanged in the last 1.6 million years. The ancient Antarctic assemblage has been different from the then fauna of the low latitudes, but the difference was not so striking as it is now. The ancient fauna of the Antarctic Sea may be regarded as the temperate one.

The recent radiolarian fauna of the low latitudes of the Indian Ocean is older than the Antarctic fauna. About 2.5 to 2 million years ago the fauna of the low latitudes was very much the same as the recent, both as to the set of genera and species, and as to the population size.

It is evident that in the last 3 million years the rapidity of the evolution of the radiolarian fauna was different in the high and low latitudes of the Indian Ocean.