Early history ofBolivinita pliozeaFinlay (Foraminiferida, Neogene, New Zealand)

Abstract

The benthic species Bolivinita pliozea is widespread in upper Tongaporutuan and Kapitean strata (upper Miocene), appearing above strata in the Tongaporutuan name-bearer but below those in the Kapitean name-bearer. Its appearance is traced in detail in the Blind River column, Marlborough, where pliozea variants appear in B. pohana populations and gradually become dominant. Modifications to the shell include reduction in spiral obliquity, increase in convexity of the distal walls, and greater development of ribs. A biometric representation is given. A regional survey shows that B. pliozea is usually preceded by B. pohana or by B. cf. pohana. Several isolated records of B. pliozea lower in the Tongaporutuan are taken as local developments of pliozea variants in B. poh,ana populations. The widespread occurrence of B. pliozea in upper Tongaporutuan and higher strata represented a permanent shift in the variation pattern.