The Cycadales have been present on the Earth long enough to have experienced (and survived) two major worldwide extinction events (at the beginning and end of the Mesozoic Era), as well as one major glaciation in the Permian period and four in the Pleistocene. They have also rafted about the world on continental fragments driven by relentless tectonic forces. When the continents were fused and the world's climate was mild, the Cycadales flourished nearly worldwide from Greenland to Antarctica (Note: the continents were not at their present latitudes at that time). When the ice ages made much of the higher latitudes frozen wastelands, populations unable to retreat south (or north, in the case of Pterosoma in Australia and Tasmania) because of rift valleys, oceans and mountain barriers like the Alps, Andes, Dolomites and Pyrenees, perished in the cold. In Asia, ancient cycad habitats were lifted to inhospitable heights by the birth of the Himalayas. In South America, the uplift of the Andes and glaciers advancing from the south caused cycads to retreat north to refugia in the tropics.

There were also barriers in the good times. It is curious that although South America and Africa were joined during the Jurassic, Encephalartos is not present today in Brazil (although fossil material hints at the presence of a close relative in North America and Argentina during the Tertiary Period) and Zamia shows up nowhere in Africa. Was this range inhabited by an early precursor of both genera and their divergence only occurred at the close of the Jurassic period as that common range was broken apart? Or perhaps Encephalartos reached North and South America by different routes, and was unable to penetrate Central and northern South America due to geologic barriers. Fossil material dating from the Jurassic found in Yorkshire in Great Britain and attributed tentatively to Encephalartos suggests this may have been the doorway to North America for Encephalartos. During a 150- million-year isolation, perhaps the surviving antecedents of Encephalartos in the Americas were gradually transformed into Dioon, what we know today as a close relative of Encephalartos.