The -first most acute phase of faimal deterioration coincides with the 

 invasion of a small but significant assemblage of cool-water molluscs 

 (Fleming, 1944) and probably with the earliest recorded glaciation in 

 New Zealand (Gage, 1945). The second (Okehuan) deterioration has not 

 previously been attributed to a cold phase. The two Hawera series 

 faunas certainly fall into a period of time when glacial advances occurred 

 in mountainous areas, but they are from " raised beaches " and thus 

 more likely to be interglacial than glacial (Zeuner, 1946, p. 129). 



In periods of oceanic cooling in New Zealand, invasions of sub- 

 antarctic mollusca could perhaps not counterbalance the extermination 

 of subtropical ones, for the subantarctic fauna is relatively poor in genera 

 and species, and contains a high proportion of rock and kelp inhabiting 

 forms which are seldom preserved as fossils. Many subtropical genera, 

 on the other hand, have vagile pelagic larvae and live in stations which 

 are preserved, so that the warmer phases of post-Miocene time have left 

 a more distinctive record than the cooler. 



Faunal Provinces 



The present Indopacific fauna has sometimes been considered the 

 living representative of the Miocene faunas of temperate seas, just as 

 the mammal fauna of Africa has been dubbed a surviving Pliocene fauna. 

 In the same way past marine faunas in New Zealand have close analogies 

 with contemporary provincial faunas. The time has not yet come for 

 biometric analyses of New Zealand fossil faunas such as have been made 

 in California by Schenck and Keen (1937). Such analyses would establish 

 a probable latitudinal or isothermal equivalent, in Recent times, for 

 a past fauna. The analogies between living and extinct faunas are, 

 however, close enough to suggest a sequence of events illustrated in 

 Fig. 5. This diagram is based on faunal changes in the Cook Strait 

 area, the modern " Cookian Province." The early Pliocene faunas 

 contained genera (such as Polinices, OUvella, Cheilea, Sinuni, &c.) 

 suggesting conditions more tropical than those of the Aupourian of 

 to-day. The cool water fauna of the Hautawan (Lower Nukumaruan) 

 can be compared with the Forsterian of southern New Zealand, and the 

 succeeding warm faunas of the Marahauan (Upper Nukumaruan) show 

 a return to subtropical conditions (Pterochelus , Ataxocerithhim, Ella- 

 trivia, Isognomon, &c.). After the second (Okehuan) period of inferred 

 cooling the warm Putikian saw the arrival or return of genera nov/ 

 limited to the Aupourian or even warmer coasts .{Zelippistes, Pterochelus, 

 Anadara, Eiinaticina, &c.). Later faunas are Cookian, but there are 

 a few Aupourian forms in the second Hawera stage. Figure 6 shows 

 in map form the extent of the movements of provincial boundaries 

 implied by the analogies drawn. 



It would not be possible to interpret the fossil record in terms of past 

 oceanographic conditions if there were no correlation between environ- 

 ment and fauna, but there are plenty of anomalies. In particular it 

 has been found in Europe as well as New Zealand that newcomers to 

 a fauna, colonizing under the influence of a favourable environment, 

 may survive the following opposite fluctuation, even if this survival 

 entails tolerance of conditions previously intolerable. Such survivals 

 are known in the fossil record, and help to explain the anomalous 



315 



