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The Age of Dinosaurs

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Setting the Stage The Mesozoic Era is the Age of the Dinosaurs and lasted almost 180 million years from approximately 250 to 65 mya. This era includes 3 well known periods called the Triassic, Jurassic, and Cretaceous periods. A mass-extinction marked the beginning and end of the Mesozoic Era. The event that caused the transition from the Paleozoic era to the Mesozoic era, The Permian Extinction was the greatest extinction this earth has seen. This extinction wiped out about 95% of all marine life and 70% of land-life. This allowed the dinosaurs to diversify and enter niches left unoccupied by the Permian Extinction. The era ended with "The Great Extinction" which marked the end of the dinosaurs as the Cenozoic era began.

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Arrangement of Continents At the beginning of the Mesozoic, all of the world's continents were combined into the supercontinent of Pangaea, which rifted into Laurasia in the north and Gondwanaland in the south. By the end of the era most of continents had separated into their present form.

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Estimated Global Temperatures in the Proterozoic Eon

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Triassic During the Triassic, the Earth's land mass was a single supercontinent called Pangaea ("all the land"). Pangaea was surrounded by the world-ocean known as Panthalassa ("all the sea"). The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The Earth's biosphere impoverished; it would take well into the middle of the period for life to recover its former diversity. Therapsids and archosaurs (reptiles) were the chief terrestrial vertebrates during this time. Time 251 - 199 million years ago (Mesozoic Era)

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Triassic Biology The oceans teemed with the coiled- shelled ammonites, mollusks, and sea urchins that survived the Permian extinction and were quickly diversifying. The first corals appeared, though other reef-building organisms were already present. Giant reptiles such as the dolphin- shaped ichthyosaurs and plesiosaurs preyed on fish and ancient squid. Pterosaurs, a group of flying reptiles, took to the air. On firm ground, moss, liverwort, and ferns carpeted forests of conifers, ginkgoes, and palm-like cycads.

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Triassic Biology - The First Mammals But perhaps the biggest changes came with the evolution of dinosaurs and the first mammals in the late Triassic, starting around 230 million years ago. One of the earliest true mammals was the three-foot-long (one- meter-long) Eozostrodon. The shrew-like creature laid eggs but fed its young mother's milk - a monotreme like todays echidna or platypus. While dinosaurs dominated many ecological niches, mammals remained small. Therapsids - reptiles that had developed some mammalian characteristics

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Triassic Biology - The First Dinosaurs Among the first dinosaurs was the two-footed carnivore Coelophysis, which grew up to 9 feet (2.7 meters) tall, weighed up to a hundred pounds (45 kilograms), and probably fed on small reptiles and amphibians. It showed up about 225 million years ago. A few million years later came the 27.5-foot-long (8- meter-long) herbivore called Plateosaurus.

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Triassic Geology During the Triassic, almost all of the Earth's land mass was combined into a single supercontinent called Pangaea (All the Land) which straddled the equator From the east a vast gulf entered Pangaea, the Tethys sea. Mean atmospheric O2 content over period duration ca. 16 Vol % (80 % of modern level) Mean atmospheric CO2 content over period duration ca. 1750 ppm (6 times pre- industrial level) Mean surface temperature over period duration ca. 17 C (3 C above modern level)

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The End of the Triassic This period ended with another mass extinction, followed by volcanic eruptions about 208-213 million y.a. The suspected cause is global warming related to the increase in volcanism. During this extinction, Pangaea began to break apart. As a result of the extinction, 35% of all families died out. Dinosaurs, however, survived and went on to dominate the Jurassic.

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Jurassic The Jurassic is named from the Jura Mountains of the Alps. The Jurassic constitutes the middle period of the Mesozoic Era. The start of the period is marked by the major Triassic Jurassic extinction event. Two other small extinction events occurred during the period Time 199 - 145 m.y.a (Mesozoic Era)

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Jurassic Geology During the early Jurassic period, the supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern supercontinent Gondwana The Gulf of Mexico opened in the new rift between North America and what is now Mexico's Yucatan Peninsula. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous period, when Gondwana itself rifted apart.

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Jurassic Geology By subduction of the oceanic plates, mountains began to form along the west coast of North America. Throughout the Middle to Late Triassic, mountains continued to form along the coast extending from Alaska to Chile. The Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed.

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Jurassic Biology On land, the Triassic reptiles to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of suarischian theropod dinosaurs. Other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Gymnosperms (plants with cones (Conifers)) appear.

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Dinosaur Evolution Dinosaurs evolved along two lines - the Ornithiscian or bird-hipped dinosaurs and the Saurischian or lizard hipped dinosaurs. Predators such as Velociraptors and T. Rex, and massive dinosaurs such as Brachiosaurs were Saurischians. Dinosaurs such as Triceratops, Stegasaurus and horn-billed dinosaurs were examples of Ornithischians Ironically, birds evolved from Saurischians.

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Jurassic Geology By the beginning of the Jurassic, Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, and many of the arid deserts of the Triassic were replaced by lush rainforests. Mean atmospheric O2 content over period duration ca. 26 Vol % (130 % of modern level) Mean atmospheric CO2 content over period duration ca. 1950 ppm (7 times pre- industrial level) Mean surface temperature over period duration ca. 16.5 C (3 C above modern level)

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Two Dinosaur Cladograms

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Cretaceous The Cretaceous derived from the Latin "creta" (chalk), usually abbreviated K for its German translation Kreide (chalk). The Cretaceous is followed by the Cenozoic era. It is the last period of the Mesozoic Era, and, spanning 79 million years, the longest period of the Phanerozoic Eon. The Cretaceous was a period with a relatively warm climate, resulting in high sea levels and creating numerous shallow inland seas. This era was warm and moist with excellent conditions for abundant life on land almost from pole to pole. Extremely warm oceans may have lead to anoxic conditions in deep water. (very low O2 levels toxic to marine life) Time 145 - 65 million years ago (Mesozoic Era)

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Cretaceous Biology The oceans and shallow inland seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. At the same time, new groups of mammals and birds, as well as flowering plants, appeared. Flowering plants (angiosperms) spread during this period, although they did not become predominant until late in the Cretaceous. The first representatives of many leafy trees appeared in the Cretaceous.

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Cretaceous Biology The evolution of plants was aided by the appearance of bees; in fact angiosperms and insects are a good example of coevolution. High oxygen levels produced giant insects. However these may have gone extinct with the appearance of birds. On land, mammals were a small and still relatively minor component of the fauna. Early marsupial mammals evolved in the Early Cretaceous, with true placentals emerging in the Late Cretaceous period. An actual Velociraptor - much smaller, feathered compared to the movie version

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Cretaceous Dinosaurs Dinosaurs continue to diversify. Birds evolve from the small therapod predators that we know as raptors. These dinosaurs develop feathers (probably for insulation and display) and gradually develop into gliders then fliers. The Tyrannasaurus Rex appears in the late Cretaceous and exists until the K-T extinction event.

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Cretaceous Geology During the Cretaceous, the former supercontinent of Pangaea completed its tectonic breakup into present day continents, although their positions were substantially different at the time. The Atlantic Ocean widened. Though Gondwana was still intact in the beginning of the Cretaceous, it broke up into South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other)

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Cretaceous Geology Thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. At the peak of the Cretaceous, one-third of Earth's present land area was submerged.

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Cretaceous Geology During the Cretaceous Gondwana breaks into South America, Antarctica, and Australia, Africa, India and Madagascar. Laurasia breaks into North America, Europe and Asia. The map of the Late Cretaceous shows most of todays continents. Mean atmospheric O2 content over period duration ca. 30 Vol % (150 % of modern level) Mean atmospheric CO2 content over period duration ca. 1700 ppm (6 times pre- industrial level) Mean surface temperature over period duration ca. 18 C (4 C above modern level)

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The Cretaceous Extinction The K-T (Cretaceous - Tertiary) extinction event is widely known as it marked the end of dinosaurs. Two major geological upheavals occurred at this time approximately 65 million years ago - the volcanic event known as the Deccan Traps flood basalts and the Chicxulub meteorite which struck the Yucatan Peninsula in Mexico.

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Deccan Traps The Deccan Traps formed between 60 and 68 million years ago, at the end of the Cretaceous period. The major part of this event occurs at the K-T boundary. This series of eruptions may have lasted less than 30,000 years in total. The original area covered by the lava flows is estimated to have been as large as 1.5 million km, approximately half the size of modern India. These layered basalts are over a mile deep in places. The eroded sediment from this rock is responsible for fertile soils.

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Deccan Traps The Deccan Traps are an example of an LIP (Large Igneous Province) where basalts have flooded over continental land masses. There are several throughout the world (including the Siberian traps and the Columbia Flood Basalts of the western USA) These events are thought to release large amounts of CO2 and atmospheric pollutants which could drastically change climate.

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Evidence of the K-T extinction event The Cretaceous-Tertiary extinction event, or the K-T event, is the name given to the die-off of the dinosaurs and other species that took place some 65.5 mya. For many years, paleontologists believed this event was caused by climate and geological changes that interrupted the dinosaurs food supply. However, in the 1980s, father-and- son scientists Luis (1911-88) and Walter Alvarez (1940-) discovered in a distinct layer of iridiuman element found in abundance only in spacethat corresponds to the precise time the dinosaurs died. Walter and Luis Alvarez standing at the Gubbio Clay layer, the K-T boundary rich in Ir and microtektites.

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Chicxulub Crater This suggests that a comet, asteroid or meteor impact event may have caused the extinction of the dinosaurs. In the late 1980s, petroleum geologists working for PEMEX located an arc shaped gravitational anomaly in the Gulf of Mexico. What they had found was the massive Chicxulub Crater at the tip of Mexicos Yucatn Peninsula, which dates to the K-T boundary.

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Chicxulub Crater The crater is not visible at the Earths surface as it is buried in 65 million years of new marine sediments. Seismic and gravitational anomaly images taken in the 1990s give a clear picture of the location of the crater. Additionally, it turns out that limestone sinkholes called cenotes perfectly line the edge of the crater. Artists rendering of the crater after it was formed

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Alternate Theories Besides dinosaurs, many other species of mammals, amphibians and plants died out at the same time. Over the years, paleontologists have proposed several theories for this extensive die-off. One early theory was that small mammals ate dinosaur eggs, thereby reducing the dinosaur population until it became unsustainable. Another theory was that dinosaurs bodies became too big to be operated by their small brains. Some scientists believed a great plague decimated the dinosaur population and then spread to the animals that feasted on their carcasses. Starvation was another possibility: Large dinosaurs required vast amounts of food and could have stripped bare all the vegetation in their habitat. But many of these theories are easily dismissed. If dinosaurs brains were too small to be adaptive, they would not have flourished for 160 million years. Also, plants do not have brains nor do they suffer from the same diseases as animals, so their simultaneous extinction makes these theories less plausible.

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K-T Extinction Videos http://www.history.com/topics/why-did-the-dinosaurs-die-out History Channel http://www.youtube.com/watch?v=ubBebEywNmE (KT Asteroid & Dinosaurs Extinction) (7:05) http://www.youtube.com/watch?v=ubBebEywNmE http://www.youtube.com/watch?v=_COcHHvte-0 (2:25) (meteorite strike) http://www.youtube.com/watch?v=_COcHHvte-0 http://www.youtube.com/watch?v=Dcp0JhwNgmE (Chicxulub Tsunami (4:05)) http://www.youtube.com/watch?v=Dcp0JhwNgmE http://www.youtube.com/watch?v=4WwJL25xVG8 (K-T extinction event - 44:44) http://www.youtube.com/watch?v=4WwJL25xVG8 http://www.youtube.com/watch?v=uTvFzm3jRCU (The Siberian Traps and the Volcanic Mass Extinction Theory (Full Documentary) - Permian extinction) http://www.youtube.com/watch?v=uTvFzm3jRCU