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Early Permian during continental break-up, and during the Cretaceous when seas began to rise and the established climate zones, feeding habitats and migration routes were disrupted. The extinction of the dinosaurs is a contentious issue. The Cretaceous period coincided with a period of enlargement of con- tinental seas, accompanied by a rise in sea-level, an increase in size of the modern oceans and progressive climatic disruption. Sea levels peaked on the continents during the Late Cretaceous, but this was followed by a rapid draining of continental seas to the present as the modern oceans continued to open. Expanding Earth models suggest there may have been two or more separate oceans existing during the Mesozoic era, with the possibility of separate sea levels. Rifting and merging of these oceans coincides with faunal and floral extinction events at the end of both the Triassic and Cretaceous periods. This suggests that the cause of the dinosaur extinction—which, incidentally, occurred over a period of 8 to 10 million years—may be linked with periods of rapid sea-level change rather than an inferred asteroidal impact event. The ancient Permian fern Glossopteris is a common fossil in coals throughout the southern hemisphere and has traditionally been used to define the ancient Gondwana continent. The distribution of glossopteris ferns is centred on localities in South Africa and adjacent India. During the Permian period, East Antarctica straddled the equa- tor and was located adjacent to South Africa. East Antarctica was surrounded by occurrences of glossopteris in Australia, West Antarctica and India. This suggests that glossopteris flora may have been extensive beneath the present East Antarctic ice-cap. The Permian glossopteris flora plotted on expanding Earth models straddle the palaeo-equator and range from high-northern to high-southern latitudes on the Gondwana supercontinent. This suggests that glossopteris flora were tropical to cool-temperate species, confirming the fossil evidence which shows a Gondwana climate commencing with an ice age and passing through a cold but wet temperate to warm temperate climate during the Late Palaeozoic. The palaeobiogeographic examples used illustrate the ease and simplification of migration, development of faunal and floral species and influence of climatic and geographic change on an expanding Earth. These interrelationships between global and provincial distributions are maintained without the need for com- plex conventional continental assemblage-dispersal requirements. During continental break-up and opening of the modern oceans, From Earth, by Frank Press and Raymond Siever (W. H. Freeman & Co., 1978, 2nd edition) Earliest hominids qa combat 56 = NEXUS APRIL — MAY 2001 www. nexusmagazine.com