Most dinosaur species lived and died out during this period, but
at the end of the Cretaceous period
(65 million years ago),
all remaining
types of dinosaurs
(with the exception of birds which
had already evolved, and are widely believed to be descended from dinosaurs)
died out.
At the same time many other creatures
(for example
Ammonites,
and Belemnites,
as well as
Pterosaurs,
and many large marine reptiles such as
Mosasaurs.
Plesiosaurs and
Pliosaurs)
also became extinct.
In fact,
all animals
weighing more than 55 pounds (25 kilograms) seem to have died out!
While are not sure what happened, we do know that something happened at about
65 million years ago. This
event shows up as clear boundary in the rocks, known as the "K-T boundary",
the extinction event usually being referrred to as the
"Cretaceous-Tertiary mass extinction".
Scientists have proposed many different possible explanations
for what may have happened, and
why this mass extinction might have happened:
(Note: Sometimes these suggested explanations are informally called "theories", however in this case
"hypotheses" is the correct term, since in science a theory
means a well-substantiated explanation of some natural phenomenon or observation,
whereas as "hypothesis" means a suggested explanation which needs
to be tested against experimental evidence).
Effect: Apart from the immediate impact of fires and flooding (if it hit the sea), this would have
caused catastrophic changes in the environment because of the dust thrown up in to the air blocking out sunlight.
Our Evaluation: This is currently the most popular hypothesis with scientists, because,
as
Luis and Walter Alvarez
pointed out,
iridium (which comes from asteroids) has been found all over the world
in rocks at the K-T boundary (which were laid down at
the time of the mass extinction).
There is also a large
crater at Chixulub in southern Mexico,
which appears to be of the right age,
and could have been made as a result of an asteroid hitting the earth.
Hypothesis: Volcanoes (there is known to have been very active volcanic around this time, especially in
India in a region that is today known as the Deccan Traps) could have caused catastrophic changes in the environment.
Effect: The dust from volcanoes would have affected the climate, sulphur from
volcanoes could have caused immensely strong acid rain, and poisonous
substances such as selenium could have been released into the atmosphere.
Our Evaluation: After the Asteroid Impact Hypothesis,
this is probably the second most popular explanation among scientists - partly, because we know that
volcanoes were active at about this time.
Supernova Hypothesis
Hypothesis: A nearby star exploded as a supernova.
Effect: A nearby supernova would have bathed the earth in deadly radiation.
Our Evaluation: If this hypothesis is true, rocks at the K-T boundary should contain 244Pu (a long-lived isotope of Plutonium). However, this does not seem to be the case.
Climatic Change Hypothesis
Hypothesis: Changes in the Earth's climate caused the mass extinction.
This could have been caused by gradual changes in the positions of continents
effecting ocean currents and winds, or by changes in the Earth's orbit around
the sun, or even by a relatively sudden greenhouse effects.
Effect: Depends on the particular climate change theory in question.
Our Evaluation: This hypothesis can not be discounted, and even if climate change was not
the main cause of the extinction, it could have played a part -
there is some evidence that the Earth cooled at the end of the
Cretaceous period.
Flowers Drugged the Dinosaurs Hypothesis
Hypothesis: The first flowering plants appeared during the
Cretaceous period,
and if dinosaurs ate them they could have been drugged by them.
Effect: Could perhaps have wiped out some dinosaurs.
Our Evaluation: This hypothesis does not explain the extinction of many other species, especially
marine species. It also struggles with the fact that dinosaurs and flowering
plants were contempories for many millions of years, and only suddenly, at
65 million years ago, the dinosaurs died out.
Effect: Could perhaps have wiped out some dinosaurs.
Our Evaluation: This used to be a popular hypothesis -
but does not explain the extinction of many other species, especially
marine species. It also does not explain why dinosaurs were very successful
for millions and millions of years, during most of which time, mammals were also around.
Caterpillars Ate All the Plants Hypothesis
Hypothesis: Caterpillars ate all the plants and there was not enough food for
herbivores, and eventually not enough meat for carnivores.
Effect: Could perhaps have wiped out some dinosaurs.
Our Evaluation: This hypothesis
does not explain the extinction of marine species, and some may wonder whether
caterpillars could really affect every continent on the Earth at the same time
to this extent.
Disease Epidemic Hypothesis
Hypothesis: The dinosaurs could have been wiped out by a disease epidemic.
Effect: Could perhaps have wiped out some dinosaurs.
Our Evaluation: The
problem with this hypothesis, is could it effect dinosaurs to the extent of
wiping them all out, and how could it explain the simultaneous extinction of marine animals?
Although many scientists now favor the asteroid impact hypothesis,
it is not yet
actually certain that this is the reason why the
dinosaurs died out. It is possible that
one of the other theories might be the correct one. It is also possible, that
there could have been several events which happened together, and between
them, killed all the dinosaurs.
Product Description: Written for non-specialists, this detailed survey of dinosaur origins, diversity, and extinction is designed as a series of successive essays covering important and timely topics in dinosaur paleobiology, such as "warm-bloodedness," birds as living dinosaurs, the new, non-flying feathered dinosaurs, dinosaur functional morphology, and cladistic methods in systematics. Its explicitly phylogenetic approach to the group is that taken by dinosaur specialists. The book is not an edited compilation of the works of many individuals, but a unique, cohesive perspective on Dinosauria. Lavishly illustrated with hundreds of new, specially commissioned illustrations by John Sibbick, world-famous illustrator of dinosaurs, the volume includes multi-page drawings as well as sketches and diagrams. First edition Hb (1996): 0-521-44496-9 David E. Fastovsky is Professor of Geosciences at the University of Rhode Island. Fastovsky, the author of numerous scientific publications dealing with Mesozoic vertebrate faunas and their ancient environments, is also scientific co-Editor of Geology. He has undertaken extensive fieldwork studying dinosaurs and their environments in Montana, North Dakota, Arizona, Mexico, and Mongolia. David B. Weishampel is a professor at the Center for Functional Anatomy and Evolution at Johns Hopkins University, School of Medicine. Weishampel is best known for discovering, researching, and naming several rare European dinosaur species. During the 1980s Weishampel gained fame for his work with American paleontologist Jack Horner and later named the famous plant-eating, egg-laying Orodromeus, Horner. Now, a decade after his pioneering studies with Horner, Weishampel is most widely known for his current work on the Romanian dinosaur fauna. He is the author and co-author of many titles, including The Dinosaur Papers, 1676-1906 (Norton, 2003); The Dinosauria, (University of California, 1990); and Dinosaurs of the East Coast, (Johns Hopkins University Press, 1996).
Product Description: The discovery of the giant Chicxulub impact crater, buried off the coast of Mexico, unveiled the solution to one of Earth's greatest mysteries--what killed the dinosaurs. Scientists uncovered physical evidence to explain the mass extinction that rocked the Earth 65 million years ago. Step-by-step, The End of the Dinosaurs: Chicxulub Crater and Mass Extinctions tells this great scientific detective story. Charles Frankel recounts the birth of the cosmic hypothesis, which holds that the crash of a meteor on the Earth's surface killed two-thirds of life and all the dinosaurs. He first provides a dramatic account of the impact and its aftermath. Frankel then goes on to detail the controversy that preceded the acceptance of the cosmic hypothesis, the search for the crater, its discovery and ongoing exploration, and the effect of the giant impact on the biosphere. In addition, he reviews other mass extinctions in the fossil record and the threat of asteroids and comets to our planet today. More than 70 photographs and diagrams enhance and help illustrate the material. Filled with drama and interesting science, The End of the Dinosaurs will readily appeal to both the general reader fascinated with the subject and the specialist always searching for more clues to this great mystery. Charles Frankel has written a number of articles on the earth sciences in books and magazines. His many books include Volcanoes of the Solar System (Cambridge University Press 1996).
Donald R. Prothero's science books combine straightforward research with first-person narratives of discovery, injecting warmth and familiarity into a profession that desperately needs a more appealing approach to nonspecialists. Bringing his trademark style to an increasingly relevant subject of concern, Prothero links the climate changes that have occurred over the past 200 million years to their effects on plants and animals, especially contrasting the extinctions that ended the Cretaceous period, which wiped out the dinosaurs, with those of the later Eocene and Oligocene epochs.
Prothero begins with the "greenhouse of the dinosaurs," the global-warming episode that dominated the Age of Dinosaurs and the early Age of Mammals. He describes the remarkable creatures that once populated the earth and uses his experiences collecting fossils in the Big Badlands of South Dakota to sketch their world. He then discusses the growth of the first Antarctic glaciers, which marked the Eocene-Oligocene transition. In following this dramatic transformation, Prothero shares his anecdotes of excavations and activists and illuminates the controversies between colleagues that shape our understanding of the contemporary and prehistoric world. He concludes with observations about Nisqually Glacier and other locations that prove global warming is happening much quicker than previously predicted, irrevocably changing the balance of the earth's thermostat.
Product Description: Expanded and updated This handsome book addresses the questions of what the fossil record tells us about the evolution and extinction of dinosaurs, what their relationship to the rest of the organic world was, and what we can learn from them about our own place in the history of life on our planet. This edition has been updated throughout, with a new final chapter that details exciting recent discoveries such as the feathered dinosaur fossils in China.
List Price: $7.99 Lowest New Price: $7.99 Temporarily out of stock. Order now and we'll deliver when available. We'll e-mail you with an estimated delivery date as soon as we have more information. Your credit card will not be charged until we ship the item. (As of 13:59 Pacific 4 Jul 2009 More Info)
Product Description: The first book to approach the Cretaceous extinction -the period during which dinosaurs disappeared from Earth -from the perspective of the fossil record.
Product Description: This is a comprehensive account of the life and death of dinosaurs. Modern birds, the authors assert, are the direct descendants of dinosaurs and represent the most ancient linking group of species on our planet.
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