Plastogamy and its early morphological indication in Nummulites boninensis HANZAWA from the Middle Eocene of Cambay Basin, India

Mukhopadhyay, Sanjay-Kumar

Revue de Paleobiologie 22(1): 231-242


ISSN/ISBN: 0253-6730
Accession: 012424024

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Nummulites boninensis HANZAWA population from the Middle Eocene of Cambay Basin near Vagalkhod village in Bharuch District, India has yielded a paired-test of conjoined adult individuals and a few separated adult tests representing a rare record of plastogamic union in fossil foraminifera. The paired-test showing distinctive characters observed in living plastogamic pair is probably the oldest record of sexual union in foraminifera. Of the five morphological groups, namely, symmetric lenticular, symmetric flattened, asymmetric lenticular, asymmetric flattened and post-plastogamic separated tests that comprise the population, plastogamic union was limited to the last named group. This group also shows asymmetric flattened tests like the preceeding one but differs from it in certain special morphological attributes developed during plastogamic union. The recovered paired-test and post-plastogamic separated tests belong to this group. Members of the asymmetric flattened group might represent pre-plastogamic individuals suitable for the union. The morphological features, apparently advantageous for plastogamic union grew in the tests of these two groups in the early growth stage with an irregular proloculus and the tests ultimately developed into asymmetric flattened adults.