Salient Features of the New Zealand Fauna
Long isolation from Australia has prevented land mammals from reaching New Zealand; our only endemic land mammals are two small species of bats. On the other hand, the greater part of our present land bird fauna is largely of Australian origin; the sea, however, is not a formidable barrier to creatures with well developed powers of flight. The fact remains that there is no geological evidence to suggest a direct trans-Tasman land connection with Australia at any time.
It is evident, however, that within comparatively recent geological times, transient land extensions to the north to the vicinity of Melanesia allowed the influx to northern New Zealand of fauna and flora of New Caledonian origin; not necessarily a continuous land connection, but rather a rafting effect of a series of give and take land movements.
In the flora we have the striking examples of our kauri tree (Agathis), mainly of Melanesian distribution, and a “bottle-brush” flowering shrub (Xeronema), found only in New Caledonia and islands off the North Auckland coast. In animals, there is the influx to the North Auckland Peninsula of Placostylus, a genus of large land snails, otherwise restricted to the islands of the now largely submerged Melanesian Plateau.
Archaic elements in our land fauna are the reptile tuatara (Sphenodon), the moas (Dinornis), and allied genera, the kiwis (Apteryx) and the primitive caterpillar-like arthropod Peripatus. The moa belongs to that group of large flightless Southern Hemisphere birds which includes the Australian emu, the cassowary of New Guinea, the ostrich of South Africa, the rhea of South America and the extinct Aepyornis of Madagascar. Some interconnection of southern lands in the distant past is required to account for the present wide dispersal of a group of ponderous birds ranging in height from three to 10 ft. It is hard to visualise how this dispersal was achieved, whether it developed on a formerly extensive southern continental mass, the “Gondwanaland” of geologists, whether by radial extensions of Antarctica continued to connect with these southern lands, or whether by means of “Continental Drift”, a theory which holds that the now widely separated southern lands were formerly more contiguous.
Although there is no geological record of their undoubted antiquity, a family of large primitive carnivorous land snails, the Paryphantidae, have relatives widely dispersed in southern lands, ranging from South Africa to Southern Australia, and to the islands of Melanesia and New Zealand. Our present marine fauna, also, contains elements of considerable antiquity, notably the Struthiolariidae, gastropods with living members found outside of New Zealand only in South Georgia, Kerguelen Island, and South East Australia. In the Cretaceous and in the Tertiary, the family was well represented in New Zealand and extended to Patagonia as well.
A great number of warm water genera of shellfish common in our early Tertiary formations have been exterminated during subsequent cold periods, many during the comparatively recent Pleistocene. Owing to the insularity of the New Zealand area, there was no retreating to warmer seas and, in consequence, extinctions were numerous. A notable example of a very recent extinction is in the bivalve Anadara, dead shells of which wash ashore from time to time around our northern coasts, derived from estuarine deposits and raised beaches. These bivalves were apparently completely exterminated in New Zealand during one of the cold phases of the Pleistocene, and at the same time the species suffered extinction in South Eastern Australia and Tasmania. The species, however, survived in the waters of Queensland and, with the return of warmer conditions, spread southwards again. New Zealand insularity, however, precludes its re-establishment here.
Two physical factors have a pronounced effect upon the constitution of our present marine fauna; the East Australian warm water current, already referred to, and the West Wind Drift, which sweeps the Southern Ocean, from west to east almost unimpeded. This results in an influx of sub-Antarctic organisms. Many are rafted with masses of torn-off and drifting kelp (D'Urvillea) which shelters or supports a specialised fauna, either attached to or hidden in excavations in the hold-fast. Upwelling of cold water of Antarctic origin around New Zealand, particularly on the West Coast of both islands, enables some of these sub-Antarctic genera to spread even to the extreme north of New Zealand.
Although relatively small in area, New Zealand is long and narrow, spreading over 13 degrees of latitude. This factor alone makes for a wide variety of species, many with a restricted range determined by water temperatures. Moreover, the fact that New Zealand straddles two great and distinctive water masses, the subtropical and the subantarctic, makes for relatively sharp faunal distinctions between north and south.
by Arthur William Baden Powell, Assistant Director, Auckland Institute and Museum.