THEORIES ABOUT THE EXTINCTION OF THE DINOSAURS

Why did the dinosaurs become extinct? What happened over 65 million years ago to kill a species that had survived for 150 million years? The answer is that no one knows for sure, but everyone seems to have their own favorite theory. Whatever caused the death of the dinosaurs also caused the death of about 70% of all of the species on the Earth. Now we'll introduce just a few of the popular theories dealing with the dinosaur extinction at the  end of the Cretaceous Period.

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Asteroid Impact

Asteroids very seldom pass through the earth's atmosphere, but when they do they cause mass destruction. One of the most common extinction theories is that an asteroid 4-9 miles (10 km) wide struck the earth on the tip of the Yucatan Peninsula, in the Gulf of Mexico dealing the dinosaurs a fatal blow.

Upon striking, the comet would have sent dust and steam into the atmosphere and caused huge forest fires, tidal waves, severe storms, and eliminated all sunlight. It would be six months before sunlight would reach the ground after such a blow. The dinosaurs, even in their prime, stood no chance without sunlight and plant life.

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Climate Change

The climate of the Cretaceous period was tropical. Scientists know this because nearly one half of the plants in this time were tropical plants. Many scientists believe that at the end of the Cretaceous period the temperature dropped. If this drop in temperature is correct, many of the plants that the plant eating dinosaurs ate would die and thus many of the plant eaters would die as well. If the plant eaters died there would be nothing for the meat eaters to eat and they would eventually die out also. Plankton also seemed to decrease in number during the Tertiary period which could explain the death of the marine dinosaurs that fed on them. This popular theory just possibly could have caused the dinosaurs demise.

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Volcanic Eruptions

Could numerous volcanic eruptions have caused such mass destruction? Possibly. When volcanos erupt, they send huge clouds of dust, sulfuric acid, and poisonous gases into the air making the air almost impossible to breath. The dust and ash in the atmosphere would also change the climate and sunlight levels. On top of that, the ground would be covered with layers and layers of molten rock. The dinosaurs would never have survived such a hostile, poisoned environment!

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Disease

Disease has also been proposed as the killer of the dinosaurs. As the Cretaceous period went on, more and more land bridges started to appear on the earth. The oceans started to dry up and the dinosaurs were able to walk across the land that was there. As the dinosaurs searched for food they would walk across these new land bridges and find relatives of theirs from when the lands of the world were one. But land bridges brought more than dinosaurs looking for food into the new land. They brought all of the diseases that those dinosaurs had inside of them. The diseases did not hurt those dinosaurs because they were immune to them, but to the other dinosaurs they could be fatal and the other way around. In most cases disease in a species is not fatal and is a positive thing because it will wipe out the weak so only the strong survive to pass their genes on to the next generation, but in the dinosaurs case it might not have been that way.

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Dinosaur Stress Stress on the dinosaurs is a possible solution for their extinction. This theory was first thought up by Heinrch K. Erben when he found that the shell thickness of a certain type of dinosaur species decreased as time went on. It was thought that the warm climate and good habitats in the Cretaceous period could have caused over population of dinosaurs, thus an increase of stress on the dinosaurs would develop. Stress is known to cause hormonal imbalances in modern day birds and lizards, so this could have happened to female dinosaurs. An increase of estrogen in the dinosaurs would have caused the females to lay eggs with shells too thin. If this happened it would greatly reduce the chances of the young to be hatched and live to adult hood.

Ozone Layer Depletion   The destruction of the earth's ozone layer is another proposal for the dinosaurs extinction. Hydrochloric acid from volcanic explosions (which are known to be numerous in the Cretaceous period) could have depleted the earth's ozone layer to a great extent. With the absence of this layer there would be nothing to protect the dinosaurs from the ultra violent rays of the sun. This could also explain why the dinosaurs and not the mammals seemed to die out because dinosaurs had no hair to protect them from the suns rays like the mammals of that time did.

Greenhouse Effect The "greenhouse effect" is another possible solution to the dinosaurs demise. Massive volcanic eruptions could have released so much carbon dioxide into the atmosphere that it caused a drastic increase in the world wide temperature. Some deep sea drills have shown that the temperature of the ocean increased 65 million years ago so the temperature of the atmosphere also likely increased. The excess carbon dioxide from the eruptions in the atmosphere would have permitted the sun's heat into the earth's atmosphere, but would have blocked most of the heat from exiting the earth's surface back into space. This would have created a "greenhouse effect", the increase in temperature could have killed the tiny plankton responsible for converting most of the earth's carbon dioxide into oxygen which would further compound the problem. Only a few degrees increase in the temperature can affect the fertility of an animal by affecting their ability to produce fertile sperm.

Supernova Could a supernova have been responsible for the death of the dinosaurs? A supernova is an exploding star. It can blast material huge distances into space. Some scientists think cosmic radiation caused by the explosion would cause extremely high rates of deadly cancer among the dinosaurs. Others believe the radiation reacted with the Earth's atmosphere and destroyed the ozone layer. Without the ozone layer to filter out dangerous radiation, once again high rates of cancer could have occurred within the dinosaurs. Only small animals and plants, whose homes were sheltered from the harmful radiation would have survived.

CaterpillarsCaterpillars which were believed to have evolved late in the Cretaceous period could have stripped plants of their leaves, a valuable food to the plant eating dinosaurs. If the caterpillars were able to strip all of the leaves from trees, then the plant eaters would not have anything to eat and would die. If the plant eaters died then the meat eaters would die from lack of food. Beware, this theory is thought to be extremely unlikely for caterpillars would have to strip all of the trees around the world of their leaves at virtually the same time.

Other Theories Ø  The climate became too dry, making the environment too arid for the dinosaurs. Ø  Multi-layer egg shells formed, with two or three shells on individual eggs, suffocating the embryos. Ø  There is evidence that many of the large dinosaurs, must have had very small brains compared to their body size. With such small brain capacity responses to the surrounding environment would have been so slow that they could not compete with faster thinking animals. Ø  Mass flooding destroyed important dinosaur habitats. Ø  Dinosaur overpopulation could have resulted in severe competition and rivalry. Ø  Mammals ate the dinosaur eggs preventing new generations surviving. Ø  Carnivores over-killed their prey, and had nothing to eat. Ø  Uranium leaked from the soil causing poisoning to the dinosaurs. Ø  High levels of carbon dioxide destroyed the dinosaur embryos

3. The Cretaceous Period

The Cretaceous Period

144 to 65 Million Years Ago

The Cretaceous is usually noted for being the last portion of the "Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first ceratopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants.

Ceratopsian

Pachycephalosaurus

The breakup of the world-continent Pangaea, which began to disperse during the Jurassic continued. This led to increased regional differences in floras and faunas between the northern and southern continents.

The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. This laid open the stage for those groups which had previously taken secondary roles to come to the forefront. The Cretaceous was thus the time in which life as it now exists on Earth came together.

The age of dinosaurs reached its apex during the Cretaceous period, which occurred 145 to 65 million years ago. Dinosaur and other animal diversity characterized this time, as more different types of dinosaurs emerged during the Cretaceous than in any other period. Nevertheless, ominous signs began to surface, hinting at the non-avian dinosaur downfall that would mark the end of this final phase of the Mesozoic era.

Cretaceous Geology, Climate and Plant Life

Laurasia, a portion of the former Pangea supercontinent, consisted of the present-day continents of North America, Europe and much of Asia. Another section of former Pangea was referred to as Gondwana, which included Africa, Antarctica, Arabia, Australia, India and South America. Both Laurasia and Gondwana broke into pieces during the Cretaceous, leading to the separate continents. North America, however, was substantially different than it is today. A shallow sea split it in half, turning the western portion into an island.

Although wet and dry periods existed before this time, the seasons became more distinct during the Cretaceous. Flowering plants emerged, providing another food source for dinosaurs. The first flowers were mostly like small weeds but, like weeds today, they grew and spread well, quickly moving from tropical to cooler regions. Oak, maple, walnut and other trees also emerged.

The Largest Flying Animals

Pteranodon

Cretaceous skies were full of creatures big and small. Minuscule moths and small bees shared airspace with enormous pterosaurs, which were warm-blooded flying reptiles related to dinosaurs. The pterosaur Pteranodon, which had a wingspan of up to 33 feet, was one of the biggest of the bunch. It spent much of its time soaring over water, looking for fish, crabs, insects and mollusks to eat.

Dinosaur Diversity

Big, small, spiked, fat and more, dinosaurs of all shapes and sizes appeared during the Cretaceous. Since the landmasses were now separated, animals on the distinct continents went their separate evolutionary ways. Beaked, plant-eating dinosaurs known as ceratopsians first appeared at this time. One of the most well-known members of this group was Triceratops, which had three facial horns and a large, bony frill. The so-called "bone-headed" dinosaurs also emerged during the Cretaceous. One of the biggest was Pachycephalosaurus, which had front teeth and might have even enjoyed meat with its plant-based diet.

Ceratopsian

Triceratops

Pachycephalosaurus

Numerous carnivorous dinosaurs preyed upon the other dino bounty. There was Pelicanimimus, which had more teeth — around 220 — than any other known dinosaur. Afrovenator used its own bladelike teeth to tear at the flesh of prey. Carnotaurus had such short arms that its hands appeared to form out of its elbows, but its clawed feet and sharp teeth could still take down sauropods. Tyrannosaurus rex, however, stood out from the carnivorous dinosaur pack. This 40-foot-long beast was so strong that researchers believe it could shake victims to death, once it had sunk its teeth into their bodies.

Pelicanimimus

Afrovenator

Carnotaurus

T-Rex

The Cretaceous period marks the end of the age of Dinosaurs with what is known as the Great Extinction. However, this period gives us some of the most beloved dinosaurs of modern days, like the Triceratops and, of course, the Tyrannosaurus-rex, king of the dinosaurs.

Hints of Extinction

Not all dinosaurs thrived during the Cretaceous. Stegosaurs, which lacked the protective armor of other plant eaters, like ankylosaurs, went into a population decline. In northern areas, long-necked sauropods began to disappear. While minor, these changes might have foreshadowed the mass extinction that marked the end of both the Cretaceous period and the dinosaur age.

Ankylosaurs

Sauropods

The Great Extinction

 

While the cause of the massive extinction brought on at the end of the Cretaceous period is debated, many theories exist. There is evidence of plant decay which would have contributed to the extinction, as all dinosaurs, whether directly or indirectly, depended on plant life. This could have been caused by large asteroid collisions or volcanic eruptions or both. These events would have suspended sunlight, causing plant life to diminish. Other theories include the regression of the sea level, or a combination of many of these possibilities. Most of the species that survived were not as dependent on plant life. Insects survived on other animals and dead organisms and mammals would often feed on insects. This allowed the Mammals to survive until the present day when mammals would replace the dinosaurs as the dominant species.

2. Dinosaurs of the Jurassic Period

Jurassic Period

A period of the Mesozoic era, spanning the time between the Triassic and the Cretaceous periods, about 206 to 144 million years ago. The start of the period is marked by the major Triassic-Jurassic mass extinction. Named for the Jura Mountains on the border between France and Switzerland, where rocks of this age were first studied, the Jurassic became a household word with the success of the movie Jurassic Park – although most of the dinosaurs featured in the film actually lived during the Cretaceous.

reptiles dominated the land, sea, and air. During this period, vegetation was greener and more lush. By the late Jurassic, great dinosaurs such as Brachiosaurus, Allosaurus, Ceratosaurus, and Stegosaurus, had evolved on land. Pterosaurs ruled the skies and the earliest known birds appeared.

The Jurassic was the beginning of the age when reptiles dominated the land, sea, and air. During this period, vegetation was greener and more lush. By the late Jurassic, great dinosaurs such as Brachiosaurus, Allosaurus, Ceratosaurus, and Stegosaurus, had evolved on land. Pterosaurs ruled the skies and the earliest known birds appeared.

The Jurassic Period also saw the breakup of the super-continent Pangea, which began in the Triassic, continue. At the start of the early Jurassic period, the giant continent Pangaea broke up, forming the beginning of the world that we now know. There were huge volcanoes with rivers of lava and clouds of poison gases.

Land that had been part of the interior of the huge continent was now coastline of smaller continents, and the climate began to change accordingly.

Forests of ferns, ginkgo trees, cycads and conifers grew. All these plants can still be seen today. Scuttling about at the bottom of these plants were the early mammals, all of them rat-sized.

Sauropods were gigantic herbivores

The dominant land animals were the huge dinosaurs, the largest land animals ever. They were the gigantic herbivore (plant-eaters) sauropods such as Diplodocus and Brachiosaurus. Other herbivores included Stegosaursaurus. Carnivorous (meat-eating) dinosaurs included Allosaurus and Dilophosaurus.

Allosaurus

Dilophosaurus

Dilophosaurus

The dinosaurs of the Jurassic were much more different from each other than in other periods: there was a greater variety. Because of the different climate, the forests grew, and the herbivores became huge in order to feed on the tall trees. The carnivores then had to become larger and more fierce to deal with such huge prey.

The first birds appeared, such as Archaeopteryx. The seas were full of marine reptiles such as the plesiosaurs, crocodiles, ichthyosaurs, sharks and rays.

The first birds the Archaeopteryx appeared in the Jurassic Period

Plesiosaurs

Ichthyosaurs

Some Dinosaurs of the Jurassic Period

1.Stegosaurus  (say steg-uh-SAW-rus)

Stegosaurus lived about 160-145 million years ago during the late Jurassic Period. It was over 8 metres long and weighed about 2 1/2 tonnes. Stegosaurus had a big tail with metre-long spikes at the end for protection against predators.The back legs were twice as long as the front legs. It had a tiny head containing a tiny brain. Its mouth was a toothless beak. It had large, flat, triangular plates along its back, rather like armour. Palaeontologists believe that the triangular plates along the back and tail helped it keep its temperature under control. They may also have been used to attract other stegosaurs. They were made of bone that was not solid, but which had tunnels like tubes along them.
The first Stegosaurus fossil was discovered in Colorado, USA in 1877.

2.Allosaurus (say all-oh-SAW-rus)

The name means 'different lizard', because its vertebrae (bones of the spine) are different from that of other dinosaurs. Allosaurus lived about 150 to 145 million years ago in the Late Jurassic period. It was about 12m long and weighed up to 3 tonnes

Allosaurus was a 'lizard-hipped' dinosaur (or theropod). It had a bony crest above each eye and an s-shaped neck. It moved on its two strong back legs.

The back legs had three toes pointing forward and one pointing backwards. It was not a fast runner however. It had a powerful tail.

Allosaurus was a carnivore with big, curved teeth that were grooved for extra sharpness. The strength in its back and neck helped its jaws tear up its prey. Allosaurus had short arms with three long claws that held onto prey such as large sauropods. Allosaurus had quite short arms compared to its legs, but they were powerful. They had three long, hook-like claws that were important for attacking and holding on to prey.

More than 60 Allosaurus skeletons have been found in Wyoming, New Mexico and Utah in the USA, and Tanzania . The most complete was found in 1883.

3.Brachiosaurus (say BRAK-ee-oh-SAW-rus)

Brachiosaurus lived about 150 to 145 million years ago in the Late Jurassic period. Its name means 'arm reptile', because its front legs are much longer than its back legs.
Brachiosaurus was a dinosaur in the group known as sauropods. It was about 25m long and about 13m high. It was able to eat from the tallest trees, feeding on leaves and fruit with its chisel shaped teeth.

Brachiosaurus was one of the biggest land animals ever, probably weighing about 80 tonnes. Good fossils have been found in Colorado, USA and Tanzania.

4.   Diplodocus (say dip-LOD-oh-kus)

The name means 'double beamed lizard' because it had extra bones to help support its spine.

Diplodocus lived about 150 to 145 million years ago in the Late Jurassic period. It was part of the group of dinosaurs known as sauropods. The Late Jurassic period was a time when there were many sauropods.

Diplodocus was a 'lizard-hipped' dinosaur that was about 45 metres long. Much of its length was the tail, which flicked like a whip. Diplodocus weighed about 30 tonnes. Its height at the hips was about 5 metres. It was the longest of the dinosaurs, but not the heaviest. Its brain was not much larger than a tennis ball, but there were many nerves in the base of its spine. This was necessary for it to cope with such an enormous size and to control its tail and back legs.

Diplodocus was a herbivore. It had peg-like teeth which it used for stripping off soft leaves such as those of ferns. The teeth were not used for chewing however. Diplodocus swallowed stones which helped grind up food in its stomach. This habit is similar to that of modern birds.

Fossils have been found in the Rocky Mountains, Montana, Utah, Wyoming and Colorado in the USA.

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