ISOTOPIC PALEOBIOLOGY OF SOME TERTIARY LARGER FORAMINIFERA FROM KUTCH, INDIA

The paleobiology of some Tertiary larger foraminifera from Kutch is in ferred using oxygen and carbon isotopic data, Spiroclypeus and Heteros tegina (having chamber-lets) show lower delta(13)C values than Nummuli tes and Assilina (having undivided chambers). This difference is attri buted to algal endosymbionts for whom division of chambers is function ally advantageous, The isotopic data also support the view that pustul es on the surface of some larger foraminifera developed to concentrate light for the benefit of endosymbionts. Isotopic variability is great er in megalospheric than in microspheric farms, indicating that the me galospheric forms are more tolerant of ecological variation than the m icrospheric ones, and this could be one of the reasons why they are mo re common in the geologic record, Similarly, variability in delta(18)O and delta(13)C isotopic values indicate that the family Nummulitidae is more stenotopic, whereas Lepidocyclinidae and Miogypsinidae appear to be more eurytopic. The order of extinction of the genera Assilina, Nummulites and Spiroclypeus also parallels the progressive decline in delta(13)C in their skeletal carbonates, This parallelism possibly ind icates a greater role for endosymbionts in the evolution of larger for aminifera.