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Dinosaur Extinction
Dinosaurs inhabited the earth for over 165 million years,
during the
Mesozoic Era.
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).
- Asteriod Impact Hypothesis
- Hypothesis: An asteriod hit the earth.
- 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.
- Volcanism Hypothesis
- 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.
- Mammals Ate the Dinosaurs' Eggs Hypothesis
- Hypothesis: Mammals ate the dinosaurs' eggs.
- 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.
Related Information & Resources
See Also
Books about Dinosaur Extinction
Here are some books from Amazon.com:
Disclosure: Products details and descriptions provided by Amazon.com. Our company may receive a payment if you purchase products from them after following a link from this website.
By BRANLEY
Collins
Released: 1991-03-15
Paperback (32 pages)
 | List Price: $5.99*
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Click Here | Product Description:
What happened to the dinosaurs?For millions of years these fantastic creatures roamed our planet. Then, suddenly, they all disappeared. Scientists wonder why. What could have caused this huge extinction 65 million years ago? In this enlarged edition, distinguished writer Franklyn M. Branley and award-winning artist Marc Simont provide the perfect introduction to an always fascinating subject - the disappearance of the dinosaurs. Outstanding Science Trade Books for Children 1989 (NSTA/CBC) |
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By Charlotte Lewis Brown
HarperCollins
Released: 2007-06-12
Paperback (48 pages)
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Click Here | - ISBN13: 9780060005306
- Notes: 100% Satisfaction Guarantee. Tracking provided on most orders. Buy with Confidence! Millions of books sold!
Product Description:
A compelling account of how the impact of a giant asteroid may have killed the Earth’s dinosaurs. |
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By David E. Fastovsky
Cambridge University Press
Hardcover (485 pages)
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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). |
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By Charles Officer
Perseus Books
Hardcover (209 pages)
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In 1980 Nobel Laureate Luis Alvarez announced his theory that the dinosaurs met their final demise when a meteorite crashed into Earth. Instantly embraced by the media, this theory became the hottest scientific "fact". However, many in the scientific community did not support Alvarez's theory. This book chronicles the fantastic story of how this hypothesis became so widespread, reveals the myriad scientific research that proves it wrong, and offers an alternative explanation for the extinctions. |
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By J. David Archibald
The Johns Hopkins University Press
Hardcover (120 pages)
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In the geological blink of an eye, mammals moved from an obscure group of vertebrates into a class of planetary dominance. Why? J. David Archibald's provocative study identifies the fall of dinosaurs as the factor that allowed mammals to evolve into the dominant tetrapod form. Archibald refutes the widely accepted single-cause impact theory for dinosaur extinction. He demonstrates that multiple factors—massive volcanic eruptions, loss of shallow seas, and extraterrestrial impact—likely led to their demise. While their avian relatives ultimately survived and thrived, terrestrial dinosaurs did not. Taking their place as the dominant land and sea tetrapods were mammals, whose radiation was explosive following nonavian dinosaur extinction. Archibald argues that because of dinosaurs, Mesozoic mammals changed relatively slowly for 145 million years compared to the prodigious Cenozoic radiation that followed. Finally out from under the shadow of the giant reptiles, Cenozoic mammals evolved into the forms we recognize today in a mere ten million years after dinosaur extinction. Extinction and Radiation is the first book to convincingly link the rise of mammals with the fall of dinosaurs. Piecing together evidence from both molecular biology and the fossil record, Archibald shows how science is edging closer to understanding exactly what happened during the mass extinctions near the K/T boundary and the radiation that followed. |
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By David E. Fastovsky
Cambridge University Press
Paperback (394 pages)
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From the authors of The Evolution and Extinction of the Dinosaurs comes an introduction to the study of dinosaurs for non-specialists designed to excite readers about science by using dinosaurs to illustrate and discuss geology, natural history and evolution. While focusing on dinosaurs it also uses them to convey other aspects of the natural sciences, including fundamental concepts in evolutionary biology, physiology, life history, and systematics. Considerable attention is devoted the nature of science itself: what it is, what it is not, and how science can be used to investigate particular kinds of questions. Dinosaurs is unique because it fills a gap between the glossy, fact-driven dinosaur books and the higher-level academic books, addressing the paleontology of dinosaurs exactly as professionals in the field do. |
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By Mark Norell & Eugene Gaffney
University of California Press
Paperback (239 pages)
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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.
ALERT: ONE LINE IS MISSING FROM PAGE XIII OF THIS BOOK. THE COMPLETE LINE SHOULD READ:
"We hope that the following pages will introduce you to some of these questions."
This error will be corrected in future editions of the book. |
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By Ph.D., Robert T. Bakker
Citadel
Paperback (480 pages)
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For over a century, dinosaurs have been thought of as plodding, dim-witted giant lizards too awkward and ill-equipped to survive the ravages of environmental change. Bakker offers startling new evidence destined to forever alter the perception of the much-maligned monsters, depicting them as never before imagined: hot-blooded, amazingly agile, and surprisingly intelligent. Illustrations. |
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By Dr. Lowell Dingus
W. H. Freeman
Hardcover (332 pages)
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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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