Some aspects of the palaeobiology of Tertiary deep-Sea Ostracoda from the S.W. Pacific

Abstract. From a numerical analysis of deep water Neogene and Quaternary Ostracoda from D.S.D.P. sites in the S. W. Pacific, it is shown that the Miocene to Quaternary interval saw a large scale invasion by bathyal stocks of the abyss. This invasion was progressive and cumulative and resulted in abyssal faunas being much more diverse in the Quaternary than they had been in the Miocene. This major palaeoecological shift also occasioned a concommitant decline in bathyal faunas over the same interval. The breakdown of bathyal and abyssal isolation resulted from the Miocene onwards, in a progressive increase in the number of species which were able, contemporaneously, to live at both bathyal and abyssal palaeodepths.

The study shows deep water faunas of this age to be much more diverse than previous studies have indicated. Ninety-one genera with autochthonous deep water species are encountered in this study. These genera are listed with the numbers of species of each genus and their depth distribution for Miocene, Pliocene and Quaternary respectively. Overall species diversity declines from the Miocene to the Pliocene but steeply increases into the Quaternary. It is suggested that the Pliocene impoverishment may in part be an artefact, occasioned by abnormally high Miocene diversity.

It is shown that the phenomena outlined above are, to varying degrees, illustrated by all of the 6 groups into which the fauna is divided. It is suggested that certain of these phenomena, such as the major downslope migration from the Miocene onwards, may be detectable in other parts of the world’s oceans.