Dimorphism and a new record of Barroisiceras De Grossouvre (Ammonoidea) from the Coniacian of Bagh, central India

Barroisiceras de Grossouvre was hitherto unknown in India. B. onilahyense B asse, which elsewhere belongs exclusively to the Coniacian, has been record ed from the Bryozoan Limestone Formation of central India. This find, as we ll as the presence of another time-diagnostic Coniacian ammonite, Placentic eras kaffrarium Etheridge and two inoceramid bivalves, Inoceramus (Mytiloid es) incertus Jimbo and I. (Platyceramus) mantelli (Barrois) Mercey in the u nderlying horizons, help in resolving the long standing problem of the age of the Bagh Group. B. onilahyense shows wide intraspecific variability and overlaps morphometrically with the late Turonian type species, B. haberfell neri (Hauer). They may be conspecific. The present species has been found t o be sexually dimorphic, a phenomenon previously not well recognised in the subfamily Barroisiceratinae. As in many Late Cretaceous ammonites, dimorph ism is manifest mainly by differences in relative adult sizes and in streng th of ornamentation, the microconch being smaller and more strongly ornamen ted.