New Caledonia And N.Z. Once Same Land Mass

Auckland Star, Volume LXXIV, Issue 34, 10 February 1943, Page 2

New Caledonia And N.Z. Once Same Land Mass

EVENTS during the past few years have brought New Caledonia very close to New Zealand. Air transport, common war aims and the fraternising of the armed forces have indeed given the illusion that space is merely relative and that the two countries are near neighbours indeed. Strangely enough, study of the fauna, flora and geology of the two countries reveals that, in the not very distant past, New Caledonia and New Zealand were geographically actually parts of the same land area.

By A. W. B. Powell

Evidence for this statement is furnished by the distribution of the kauri tree and its allies, members of the genus Agatbis, which are confined to New Zealand, the Melanesian islands and New Guinea, and thence down to Queensland via the Torres Straits islands and the Cape York Peninsula.

Corroborative evidence is furnished not only by the distribution of the plant Xeronema, of which only two species are known, one from New Caledonia and the other from our own Poor Knights Islands and the Hen Island, but also .by the circumscribed dispersal of a group of large land snails, Placostylus, which inhabit only the islands of the Melanesian area and the northern peninsula of the North Island of New Zealand.

Should further proof of the past kinship between these two lands be desired, there is other evidence, as shown by their respective plants and animals.

If we trace the present distribution of the Placostylus snails we find that, outside New Zealand, species occur at Lord Howe Island, New Caledonia, Loyalty Islands, Fiji, New Hebrides, Santa Cruz and the Solo-

mons. This vast area of distribution coincides exactly with the now partially submerged "Melanesian Plateau," a complex system of connecting land which at a moderate depth unites with the North Auckland Peninsula all the Melanesian islands where these snails occur. Deep water in the Tasman Sea separates fliis former continent from present Australia, where no snails of this type occur. In fact, this and other evidence shows that there is little real affinity between the Melanesian islands and eastern Australia, and that a yawning submerged rift, the Tasman Deep, has long operated as an effective barrier between Australia on the one hand and the Melanesian - New Zealand area on the other. New Caledonia has the greatest development of the Placostylus snail, and may well have been their point of origin from which they radiated as opportunities offered by the formation of temporary land bridges. It is not likely that man had a hand in this distribution, for minor groups of species occur which in turn are restricted to logical geographic areas. Also subfossil and fossil relatives occur in many localities, pointing to the natural distribution of these snails, long before the advent of man to the area. New Zealand has three species of Placostylus snails and a few varieties, none of which occur south of Whangarei. There is a large species formerly from the Big King Island, Three Kings group, but now extinct, another from the extreme northern tip of the North Auckland Peninsula, and a third, which once ranged down the eastern coastline from Whangaroa to Whangarei Heads. These snails live on the leaves of .the karaka and pohutukawa, and -always at no great distance from the sea, usually on coastal cliff faces. They are tall and narrow and from three to four inches in height, covered with a rich brown epidermis in life but pure white when found dead on sand dunes. Millions of bleached shells still litter the sand dunes of the Far North, but living examples have almost entirely disappeared from the mainland. The species survives in great abundance, however, on the northern island of the Poor Knights. Pigs and rats, as well as the destruction of the coastal vegetation, has killed out the species on the mainland, so it is to be hoped that the species will be saved from destruction in its last remaining island stronghold. .