Biogeographic change related to mesozoic orogenic history in the southwest pacific

Abstract

The varying proportions of different biogeographic elements among incoming, presumably immigrant, genera of bivalve and gastropod Mollusca in the New Zealand Mesozoic, are analysed in relation to orogenic movements. In the Triassic and Early Jurassic, during the later history of the New Zealand geosyncline, the high proportion of endemic genera suggests relative isolation. During precursor movements of the Rangitata orogeny (Middle Jurassic), immigration from the Tethyan region increased, and became dominant during the Upper Jurassic, just before the climax of the orogeny. Apparently orogenic movement provided shallow-water migration routes northwest of New Zealand. There was no distinctive anti-Boreal faunal province during at least part of the Upper Jurassic. During the following period of marine transgression (Upper Cretaceous), endemism increased once more, suggesting renewed isolation, and Austral elements arose, suggesting that a southern circumpolar anti-Boreal province was developed for the first time since the Permian. These changes are briefly discussed in relation to the continental drift hypothesis.