The bearing of certain palaeozoogeographic data on continental drift

Abstract

Data concerning the distribution of land vertebrates and marine molluscs from the Triassic to the present are utilised in an investigation of former continental relationships. Factors controlling the distribution of living representatives of these groups are discussed and it is indicated how regions of deep ocean restrict the distribution of the predominantly neritic molluscan faunas almost as effectively as they do land animals. Complementarity in distribution patterns in the continental and marine faunas resulting from the emergence of land bridges proves an especially useful tool in interpreting fossil distributions. The information derived from living (together with recently extinct) faunas is applied to the study of older faunas. The distribution of many Mesozoic faunas appears to demand the existence of land and/or shelf sea connections between continents where none exists today. The old concept of trans-oceanic land bridges being considered unsatisfactory, an interpretation based on Late Mesozoic and Early Tertiary continental drift is preferred, taking into account other geological and geophysical data. None of the palaeozoogeographic data surveyed is obviously incompatible with drift, and much is difficult to explain without it. Palaeozoogeographic data are thought to be especially useful in establishing a timetable for continental drift. In the hypothesis proposed it is argued that Gondwanaland did not begin to disintegrate substantially until well into the Cretaceous. The opening of the North Atlantic could possibly have taken place earlier but data are as yet inadequate to decide. The best evidence so far comes from the North Pacific region and suggests that a Bering land bridge was established by Middle or Late Cretaceous time. During the Early Tertiary the Australasian continent is considered to have moved northwards towards Indonesia and the African-Arabian continent rotated slightly anticlockwise, impinging upon Asia Minor and hence dividing the Tethyan seaway into two. The onset of a significant amount of drifting in the Middle and Late Cretaceous might be bound up with the growth of a major oceanic ridge system, which also had the effect of causing sea level to rise substantially.