3. Tertiary Migration Routes to Australasia

A Tertiary archipelago like the existing Indonesian-Malayan are, with its associated marginal shallows, and relatively narrow deeper-water gaps, would provide an adequate migration path for all the faunal movements inferred above. The movement of lineages must have been mainly southward but, as indicated, appreciable traces of northern migration out of Australasia seem discernible. This northward efflux seems to have occurred from the Miocene period onwards.

Southward migration has probably been fairly continuous since Eocene times. It appears that New Zealand had a relatively direct link with the Indo-Pacific during the greater part of the Tertiary. South-eastern Australia must have had a similar connection in the Eocene, and from Janjukian times onwards-perhaps also in the Oligocene, for which we lack evidence at present. So far as faunal movements are concerned, these links can be treated as one, and they may well have been mainly one and the same in fact. Just as we are justified in using the term “Australasian “to describe the echinoderm faunas (instead of distinguishing the two component portions), so also it would be justifiable to speak of an “Australasian” shallow-water link with the Indo-Pacific. It is desirable to make this point, since recently H. L. Clark (1946), without recourse to the fossil record, has maintained an entirely different derivation for the New Zealand echinoderm fauna from that of the Australian; his views are further considered in the next section of the present paper.