Extinction
What caused the extinction of the dinosaurs?

Extinction What caused the extinction of the dinosaurs?

Dinosaurs become extinct at the end of the Cretaceous Period.  Experts disagree about what caused their extinction.  Some believe the extinction was caused by a such as a meteorite or comet hitting the earth.  Others believe a more gradual process was responsible, such as the competition between mammals and dinosaurs, or severe climatic changes.  We're also not sure of how long it took for extinction to take place.  Some believe it happened over half a million years and others say it only took a few days.

The extinction event that killed the dinosaurs effected the entire earth!    Plants and animals on both land and in water were affected.   The disappearance of other living things was so great that scientists knew about the extinction 30 years before the first dinosaur was discovered.   The victims of the Cretaceous extinction included dinosaurs, ammonites (mollusks related to the octopus, and the chambered nautilus), pterosaurs, and certain plant groups.   But many other animal groups, even some large-bodied reptile groups like champsosaurs, were not affected.  The image of the last majestic dinosaurs passing away and leaving a world of shrew-like mammals and cold-blooded reptiles is false.   Instead, many of the major modern land animals were already living in the Cretaceous.   Dinosaurs shared their last million years with modern creatures.

Since more than just dinosaurs became extinct, reasons that only explain why dinosaurs died can be ruled out.   For instance, there is one theory that disease caused the extinction of dinosaurs.   But a disease could not have caused the extinction of plants and animals over the whole world.   There are two groups of extinction theories: catastrophic extinction and gradual extinction.    Catastrophic extinction would have been caused by a sudden, external event, such as the collision of the earth with an asteroid, or the eruption of a series of gigantic volcanoes.   Gradual extinction would have been the result of changes in the earth's land mass and climate shifts.   It could also have been because new and better animals won in the struggle for existence.

Until the recent theories about collisions, some ideas about the disappearance of dinosaurs centered around mammals beating them in the struggle to survive.   One theory suggests that mammals killed dinosaurs because they ate dinosaur eggs. Other scientists have suggested that dinosaurs caused their own extinction.   According to this theory, too many meat-eating dinosaurs evolved, eating all the plant-eaters, causing all dinosaurs to die.   These ideas have the same pitfall described earlier.   They explain dinosaur extinction but ignore the extinction of other groups.

The extinction event did not kill all animal and plant life.  Many kinds of animals survived, including fishes, frogs, turtles, crocodilians, birds, and mammals.   Scientists must take the fossil record and find reasons for all extinctions.

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