PANGAEA 227 collisional boundaries of the Pangaean blocks These are the Appalachian Mountains of eastern North America (see North America: Northern Appalachians; Southern and Central Appalachians), the Ural Mountains of European Russia (see Europe: The Urals), and the Hercynian Mountain ranges of southern Europe and parts of North Africa The Late Carboniferous was a time of vast coal swamps in the tropical latitudes There was a steep temperature gradient during the Late Carboniferous, from icy poles to hot tropics, which was more similar to today’s world than perhaps at any other time in Earth history In Gondwana, ice ages pushed glacial ice to within 30 of the palaeoequator Permian Pangaea Once assembled, at the beginning of the Permian, Pangaea stretched from pole to pole in a single hemisphere (Figure 1C) The ocean of Panthalassa covered the other hemisphere Permian Pangaea was a relatively diverse place in terms of climate and topography Permian glacial deposits found in South America, Africa, India, and Australia provide evidence of continuing glacial ages in southern Gondwana during the Early Permian Along the sutures of Pangaea, huge mountain ranges towered over vast tropical lowlands Interior areas were dry deserts where dune sands accumulated Evaporites (particularly gypsum and halite), deposited in the south-western USA and northern Europe, resulted from the evaporation of hot shallow seas and form the most extensive salt deposits in the geological record Perhaps the best testimony to the diversity of Permian Pangaea are its fossil plants, which identify several floral provinces across the vast supercontinent The coastlines of the Pangaean tropics were warm, and the waters were teeming with life The cold offshore waters of the poleward portions of Pangaea had a very different and less diverse biota The biotic extinctions (turnover) at the end of the Permian were the largest of the entire Phanerozoic (see Palaeozoic: End Permian Extinctions); they were undoubtedly influenced by the vast volcanic outpourings in Russia (the Siberian traps) and South China (the Emeishan traps) Late Permian and Triassic Intense mountain building and foreland-basin deformation took place around the Pangaean margins during the Late Permian and earliest Triassic The maximum accretion (integration) of Pangaea occurred at about the end of the Middle Triassic, approximately 230 Ma ago Early–Middle Triassic Pangaea was a much more cosmopolitan world than Permian Pangaea Triassic fossil plants indicate only two vast provinces, north and south of the palaeoequator However, some land animals, such as the mammal-like reptile Lystrosaurus (Figure 2), roamed across much of Pangaea Indeed, recognition during the 1970s of the widespread nature of Early Triassic fossils of Lystrosaurus (which are found in Russia, China, India, Africa, and Antarctica), a land animal, provided compelling evidence of the unity of Pangaea During the Triassic, the vast Pangaean supercontinent drifted northwards and rotated counterclockwise The landmass was nearly symmetrical about the palaeoequator However, no sooner had the maximum integration of Pangaea occurred, than the supercontinent began to fragment Thus, by the Late Triassic, separation of Laurussia and Gondwana had begun, with the onset of rifting in the Gulf of Mexico basin Indeed, the breakup of Pangaea began in the western Tethys and severed the supercontinent into two pieces, north and south, by the Jurassic The east–west rifting that opened up the Atlantic Ocean basin was not really achieved until the Cretaceous However, around the nascent North Atlantic basin, a huge basaltic volcanic province, called the Triassic Pangaea At the beginning of the Triassic, the Pangaean supercontinent still sat in a single hemisphere surrounded by the enormous Panthalassan Ocean Subduction zones that dipped beneath the continents nearly encircled Pangaea, and elevations were relatively high owing to regional uplift across Pangaea during the Figure Skulls of the Early Triassic mammal like reptile Lystrosaurus from northern China Fossils of Lystrosaurus are also known from Russia, India, Africa, and Antarctica, providing strong evidence of the unity of Pangaea