PLIOCENE 



PLEIST 



W A N G A N U I SERIES Ihawep/^ 



X) 



rn 

 O 



Fig. 5. — Changes in the provincial affinities of successive Pliocene and Pleistocene 

 mollusc faunas near Wanganui 



occurrence of, for instance, a group of subantarctic mollusc genera in 

 the subtropical Aupourian Province (Fleming, 1944), and others of 

 subtropical derivation in the subantarctic. 



The climatic fluctuations of late Tertiary and Pleistocene time 

 resulted in widespread changes in the distribution of organisms in 

 temperate seas, changes which continued until the threshold of Recent 

 time, and which may still be occurring. The boundaries between the 

 Recent faunal provinces, however defined, must be considered transitory 

 in terms of geologic time. Local faunas owe their constitution to the 

 complex historic processes of immigration, local extinction, and local 

 persistence, controlled in large part by past environmental change. In 

 general, however, local faunal assemblages have persisted longer than 

 the geographical faunal provinces they now inhabit. 



316 



