Labels:text | font | black and white | paper | publication | document OCR: The Triassic Period (248-208 MYA) was the first phase of the Mesozoic era ("Age of Middle Life"), often called the Age of Dinosaurs. All lands formed one huge supercontinent, known as Pangaea ("all earth"), of which the northern part is called Laurasia and the southern part Gondwana. Everywhere the climate was mild, warm, or hot: no ice sheets covered polar lands, and deserts spread into inland regions. Flowering plants had not yet evolved; conifers, cycads (palmlike tropical plants), and ferns grew in moist areas. Life on land was dominated by prehistoric reptiles (animals that have waterproof skin and lay eggs) suited to dry conditions. Reptiles also took to the air and seas. Toward the end of the Triassic Period, many of the older reptiles were wiped out, but new kinds took their place. The most successful of these proved to be the dinosaurs. LANDS Laurasia comprised North America, Europe, and much of what is now Asia. Gondwana consisted of Africa, Arabia, India, Australia, Antarctica, and South America. The South Pole was located over the ocean. The whole of Pangaea was slowly drifting north as one great landmass. This supercontinent began to show the first signs of a future breakup after the middle of the Triassic Period, when cracks started to appear in parts of eastern North America, western and central Europe, and northwestern Africa. PLANTS The plants that flourished in Laurasia were those adapted to dry climates, such as ginkgoes (trees with fan-shaped leaves), seed ferns, and cycads. The biggest trees were conifers. Ginkgoes formed an open canopy of medium- sized trees, and cycads ranged from short, squat forms to tall ones. Tree ferns created an underlying layer of vegetation in the forests, and low ferns formed savannas (tropical or subtropical grasslands with scattered trees) in drier open areas that would be grassland today. Moist, open land supported dense growths of horsetails (non-flowering, brushlike plants). Close to the equator and in drier regions, patchy conifer and cycad forests thrived. Stands of tall seed ferns formed forests in Gondwana. Later in the Triassic Period, ferns started to be replaced by cycads and conifers. LIFE ON LAND Reptiles ruled life on land during the Triassic Period. Plant-eaters included hippopotamus- like dicynodonts, squat, piglike rhynchosaurs, and mammal-like, plant-eating cynodonts. There were formidable flesh-eating cynodonts as well. Dicynodonts, rhynchosaurs, and most cynodonts died out in the first of two mysterious mass extinctions. Their place was largely taken by thecodonts (a reptile subgroup that gave rise to dinosaurs in the late Triassic Period), but these also died out, in the second of the extinctions. Survivors included turtles, land crocodilians (crocodiles, alligators, and related extinct reptiles), dinosaurs, and tiny mammals. Both of the main dinosaur groups emerged during the late Triassic Period. Among saurischian ("lizard-hipped") dinosaurs were two-legged, flesh-eating theropods ("beast-footed" dinosaurs) and four-legged, plant-eating prosauropods ("early lizard-footed" dinosaurs), the first big, high- browsing plant-eaters. Early ornithischian ("bird-hipped") dinosaurs were small, two- legged plant-eaters. With no sea to stop them, dinosaurs quickly colonized the world. LIFE IN THE AIR Small reptiles with wings of skin or scales took gliding flights from tree to tree. These "wings" may have been supported by long ribs, or they may simply have been feathery scales growing from arms and legs or webs of skin between front and hindlimbs. Late Triassic animals like these may have given rise to furry-bodied, warm-blooded pterosaurs (flying reptiles). These had a large head, a short body, and long skin wings supported by elongated fourth finger bones. Unlike their gliding ancestors, pterosaurs were capable of powered flight. LIFE IN WATER Various reptile groups invaded the shallow Triassic seas. Sharp-toothed, fish-eating nothosaurs (slender sea reptiles) with a long, thrusting tail and sharp, interlocking teeth were up to 4 m (13 ft) long and had a small head and paddlelike limbs. Seal-like placodonts (sturdy sea reptiles) crushed shellfish between broad, flat back teeth. Ichthyosaurs (streamlined, dolphinlike reptiles with fins, flippers, and long, narrow jaws), up to about 15 m (50 ft) long, were the reptiles best adapted to the sea. Among their prey were the big, swimming mollusks (soft-bodied animals without a backbone, protected by a hard shell) called ammonoids (mollusks with a large head, tentacles, and the ability to squirt water forward in order to swim backward).
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