Palaeobiogeography of mesozoic mammals - revisited

The fossil record of mammals in the Mesozoic is decidedly meagre in comparison to that of the Cainozoic, but some useful generalisations can be drawn about the biogeographic history of this group during the Mesozoic. Compared with the Jurassic, when cosmopolitanism was frequent among the mammalian families, regionalism became more pronounced in the Cretaceous, particularly the Late Cretaceous, probably reflecting the continental aggregation that produced Pangea and, subsequently Gondwana as the Mesozoic progressed. The conventional hypothesis that therians arose on the northern continents and dispersed to the southern continents reflects the poor Mesozoic mammalian record. Recent discoveries in Africa, South America and Australia suggest that caution is warranted before accepting the conventional hypothesis.