CYMOPOLIA (DASYCLADALES) FROM THE EARLY MIDDLE MIOCENE OF KACHCHH, INDIA: GLOBAL REDUCTION OF ITS SPECIES DIVERSITY IN THE NEOGENE

In the present paper, a dasycladacean alga Cymopolia miocenica is recorded for the first time from the Chhasra Formation (early middle Miocene) of Offshore Sequence of Kachchh Basin, Western India. The occurrence of this species in the early middle Miocene of Indian subcontinent is of palaeobiogeographical and biostratigrahical importance. The palaeobiogeographical distribution of this species shows clear Tethyan affinity. The presence of Cymopolia miocenica indicates that cores of the Chhasra Formation of Offshore Sequence of Kachchh Basin were deposited in warm shallow low energy marine environment. A synthesis of globally recorded 28 fossil species of Cymopolia reveals that it was originated in the Early Cretaceous. This genus shows maximum species diversification in the Palaeocene-Eocene periods whereas lowest in the Pliocene. The species diversity of this genus started declining from the Oligocene-Pliocene due to climatic changes. Only five species of this genus (C. miocenica, C. delicata, C. zitteli, C. elongata and C. rarifistulosa) were present in the Miocene. No record is available of the occurrence of Cymopolia species in the Pliocene of India and as well as in other part of the world. Only one extant species i.e. C. barbata of this genus is known from the Pleistocene. This shows continuous global species reduction of this genus and following the general trend for the whole order of Dasycladales. Present day this genus is represented by only two living species (Cymopolia barbata and C. van-bosseae).