preference for diatoms and radiolarians. Schott, in 1935 published data on the patterns of
distribution of planktonic foraminifera in tropical waters and interpreted stratigraphy of
sediments of Pleistocene age. Emiliani (1954, 1955b) deduced the paleo temperature of the
surrounding environment with the help of stable isotope method where growth of
foraminifera was based on O
isotope composition of carbonate shells.
Temperature and other water mass properties served as major factors which
determinedthe distribution of planktonic foraminifera geographically and also their
evolutionary course (e.g., Frerichs, 1971; Caron and Homewood, 1983). Sea surface
temperature fluctuations have been paralleled with the evolutionary events of planktonic
foraminifera. During the cold periods, there was a drop in the diversity of species which was
identified by the occurrence of simple trochospiral tests. Warm periods followed thereafter
witnessed species radiation as the niches left vacant were invaded and utilised by new
evolving species. Variation in shell morphology coupled with adaptive evolutionary radiation
during warm climatic conditions include development of pustules and spines, accessory
aperture, clavate chambers with tubular elongations and texture of test-surface wall, as
major identification features.
Biology of planktonic foraminifera was studied extensively by two new methods:-
Blue-water SCUBA diving methods for collection of completely undisturbed
specimens for observations in laboratory and other ecological experiments (Hamner,
1975; Alldredge and Jones, 1973).
High resolution Transmission Electron Microscope and Scanning Electron Microscope
is used to deduce the events of shell deposition and to characterize foraminiferal
cellular processes such as reproduction, digestion and relationship between host and
How Are Organisms Used As Proxies?
Foraminifera are shelled organisms found in aquatic and marine environment. Their shells
are composed up of calcium carbonate which record evidence of environmental conditions
of the past. Foraminiferal remains are obtained by taking sediment cores from oceans after
their death when their shells get buried and preserved in sediment. The chemical
composition of the shells suggests the chemistry of water when the shell was formed. Past
water temperature is inferred from stable O
isotope ratios of shells. The lighter isotopes