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The South Polar dinosaurs proliferated during the Early Cretaceous (145–100 Ma) while the continent of Australia was still linked to Antarctica to form East Gondwana, a continent that had rifted from Africa and drifted southward. Much of this southern continent lay inside the Antarctic Circle, and the climate there was unlike any that exists today. This led to fauna and flora that were unique to the time. Much of what is known about the fauna of Polar Australia comes from fossil beds found in Dinosaur Cove and Flat Rocks on the Victorian coast of southeast Australia. ==Gondwana’s climate== During the Cretaceous, Earth on average was warmer than it is now, making the polar regions more habitable. Several techniques have been used to deduce the ancient climate of Gondwana in the Early Cretaceous. One technique involves looking at the levels of oxygen isotopes in the rocks from the time. These have suggested estimated mean annual temperatures of between . The rocks with associated mammal and dinosaur fossils show evidence of permafrost, features such as ice wedging, patterning and hummocked ground. Permafrost today occurs in temperature ranges of between . Another method used to deduce the climate of the time is to use the types of plants found in the fossil record. The fossil record shows a floral community dominated by conifers, ginkgoes, ferns, cycads, bryophytes, horsetails and a few flowering plants. The plants indicated, through structural adaptations, a seasonal cold period and a mean annual temperature around (higher than found by the oxygen isotope data) and the presence of ferns and bryophytes indicates rainy conditions. A large inland sea that extended into central Australia modified its continental climate. The very lopsided distribution of land and ocean around the South Pole would have forced the ocean currents and seasonal winds (monsoons) to flow across the polar area, stopping a cold pool from forming around the pole. These studies show that during the Cretaceous there were no polar ice caps, and forests would have extended all the way to the South Pole, and life could have flourished there during the summer. However, the Earth's axial tilt means that the regions inside the Antarctic circle would still have experienced a polar night: a period of sunless darkness and cold of up to six months, during which only the hardiest life forms could survive. This combination of a habitable terrain with a long polar night is an ecological circumstance that has no present day analogue. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「South Polar dinosaurs」の詳細全文を読む スポンサード リンク
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