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Among the enduring legacies of the famous European voyages of discovery in the eighteenth and nineteenth centuries are a collection and scientific description of plants and animals from around the world. These form the nucleus of the great collections in modern museums and have been responsible for a radical revision in the way that we perceive the structure of Earth and the forces that have shaped its surface over time. As the fauna and flora from far-flung lands came to be described and incorporated into the body of knowledge about the world, it was noted that there were some striking similarities among living and extinct organisms of the Southern Hemisphere continents. In the 1840s, the English botanist Sir Joseph Dalton Hooker commented on the remarkable fact that the flora of South America and Oceania (mainly Australia, New Zealand, New Guinea, and the Malay Archipelago) shared seven families of flowering plants and 48 genera that were not to be found elsewhere. Later, similar patterns were observed in other groups of plants and animals, such as liverworts, lichens, mayflies, midges, and various types of vertebrates. How could these similarities be explained in view of the enormous stretches of ocean that separate the Southern Hemisphere continents today. One idea developed during the late nineteenth century was that there existed in the remote geological past a vast Southern Hemisphere continent – in other words, that the modern continents of the Southern Hemisphere were somehow connected long ago, thus explaining the similarities in fauna and flora.The name given to this hypothetical continent was Gondwana. One of the most distinctive fossil plants of this hypothetical continent is called Glossopteris. When first described by the French paleobotanist Adolphe Brongniart in 1828, Glossopteris was thought to be a type of fern. Now, however, it is known to be a woody seed-bearing shrub or tree. The trunks of Glossopteris could reach 4 meters in height. Seeds and pollen-containing organs were borne in clusters at the tips of slender stalks attached to the leaves, but some species may have borne seeds in cones. It is thought that Glossopteris lived in a seasonal environment, and this is consistent with the occurrence of growth rings in the wood. Also, there is evidence that the plant was deciduous (that is, that it shed its leaves annually at the end of the growing season) and that it grew under very wet soil conditions, like the modern swamp cypress. The large leaves of Glossopteris – which exceeded 30 centimeters in length – are common fossils in rocks of the Permian period (299 - 251 million years ago) in India, Africa, South America, Australia, and Antarctica. At the time the Gondwana hypothesis was conceived, the prevailing theory of Earth saw continents as fixed in their relative positions. The problem of linking up the various elements of Gondwana was solved by hypothesizing the existence of ancient land bridges. This changed in 1912 with the proposal of the theory of continental drift by the German meteorologist and geophysicist Alfred Wegener, an idea that was later developed and championed by the famous South African geologist Alex Logan du Toit. Wegener and du Toit argued that the continents are not fixed; rather, they have moved apart or drifted to their present-day positions. In the past, Gondwana was a single contiguous landmass comprising the present-day Southern Hemisphere continents. These ideas seemed incredible at the time, but in support of their theory Wegener and du Toit pointed to similarities in fauna and flora, and the distributions of fossils such as Glossopteris provided an important piece of evidence in the assembly of the Gondwana jigsaw puzzle. Wegener and du Toit also drew together other different sources of evidence, such as the remarkable geometric fit of South America and Africa, and similarities between the ages and types of rock found in areas of Southern Hemisphere continents that are now thousands of miles apart. The notion of drifting continents only became widely accepted in the 1960s following the discovery of paleomagnetism (the study of changes in the polarity of Earth's magnetic field through time) and the development of the theory of plate tectonics, which explained the growth and movement of continents and other geological phenomena.