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CONJOINED TESTS OF NUMMULITES FROM THE PALEOGENE OF THE CAMBAY BASIN, INDIA AND THEIR POSSIBLE ORIGIN

Palaeontology Division-I, Central Headquarters, Geological Survey of India, 15 A&B Kyd Street, Kolkata 700016, India. E-mail: crazytintin65{at}hotmail.com

Four specimens composed of conjoined tests—one each of Nummulites aff. discorbinus, Nummulites fabianii, Rotalia cf. trochidiformis and two of Nummulites cf. pengaroensis—were recovered from the Middle-Upper Eocene succession of the Cambay Basin, India. Each specimen comprises two mature individuals joined at their apertural areas by lime deposits. The lenticular biconvex tests of Nummulites spp. united so that their equatorial planes were either parallel, nearly coplanar or at a moderate angle, whereas the tests of the trochospiral R. cf. trochidiformis joined at their umbilical sides. The conjoined forms are not twin tests since the participating individuals are mature and have lime deposit along the junction. These forms, as well as conjoined Nummulites boninensis described in a previous report, resemble conjoined specimens of modern paired tests that united during sexual reproduction (i.e., plastogamic reproduction). This suggests the possibility that plastogamic sexual reproduction occurred in some fossil nummulitids.