Mid-latitude assemblages of Globorotalia in the late Miocene and early Pliocene of New Zealand are dominated by the G. miozea complex and its derivative taxa, most of which appear rather suddenly in the basal Pliocene. The most uninterrupted sequence, present in DSDP Site 284 on the Challenger Plateau, is closely matched in the North Island Mangapoike River section, which is correlated by biostratigraphy, geomagnetic polarity and a fission track date with Blind River in the South Island. K/Ar date of 5.2 m.y. and 5.3 m.y. for basalt associated with basal Pliocene fossiliferous deposits in the Chatham Islands support the location of the Miocene/Pliocene boundary at or close to the Gilbert/Chron 5 boundary. The isotopic record indicates that there were one or more periods of oceanic instability accompanied by cooling and polar ice accumulation in the late Miocene, immediately before the marked phase of evolutionary radiation of Globorotalia in the early Pliocene.