THE POST-MIOCENE E\^OLUTION OF MARINE FAUNAS IN 



THE SOUTH-WEST PACIFIC AND ITS BEARING ON THE 



PROBLEM OF MARINE FAUNAE PROVINCES 



By C. A. Fleming, New Zealand Geological Survej^ 



Persistence of the concept of biogeographical regions implies a consider- 

 able degree of agreement between the distribution areas of different 

 groups of organisms. Faunal bormdaries based on the distribution of 

 one group are often valid for another group, provided that such groups 

 occupy a common environment and share the same sort of dispersal 

 mechanism. For the marine fauna and flora of the continental slope 

 these conditions hold, so that conclusions based, for instance, on study 

 of moUusca are to a considerable degree valid for echinoderms or marine 

 algae. By analogy, in studies of historical biogeography we may infer 

 that faunal change in one group was paralleled in others, that the factors 

 controlling invasions, changes in distribution, and extinctions, determined 

 by study of fossils in one phylum, may apply to another phylum which 

 has left little or no fossil record. Few groups of organisms have left 

 as complete a record of their past distribution as have the marine 

 shelled mollusca, and conclusions based on their study may shed light 

 on the faunal evolution of other groups. This hope is offered as excuse 

 for the title of a paper which deals entirely with mollusca. 



Generic range charts have been compiled for the New Zealand 

 Pliocene and Pleistocene mollusc fauna, based on collections from the 

 Wanganui area, supplemented by published and unpublished information 

 from other parts of New Zealand. The information was plotted against 

 a time scale (Table 1) divided according to the system of stages used in 

 New Zealand stratigraphy (Finlay and Marwick, 1947). Substages used 

 in the Wanganui series and stages of the Hawera series have been 

 proposed elsewhere (Fleming, in preparation). The boundary between 

 Pliocene and Pleistocene is not certain, so that the local stage system is 

 used in the diagrams that illustrate this paper. 



There are some 490 molluscan genera in the New Zealand Recent 

 fauna for which some fossil record might be expected (shelled marine 

 gastropods, pelecypods, scaphopods). Only about 350 of these have 

 so far been identified as fossils, and lack of knowledge of the remaining 



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