How long ago did the dinosaurs disappear?

Based on the dinosaur fossil record, dinosaurs died out about 65 million years ago.

More recently, many scientists point out that not all dinosaurs disappeared, citing birds as direct descendants of the dinosaur. In fact, a recent study shows that birds may have survived the Cretaceous-Tertiary extinction because they had larger and more complex brains than many other contemporary animals, including the dinosaurs. Such physical features probably made survival and competition that much easier for the birds, allowing them to better adapt to the environmental changes associated with the mass extinction.

Were the dinosaurs inferior because they became extinct?

The fact that dinosaurs became extinct has been used as proof of their inferiority and that they were evolutionary failures. But it is unlikely that anyone can claim the inferiority or superiority of a species. Some species, such as the Lingula clams, have been around for 500 million years; the dinosaurs lived for about 150 million years; and the earliest hominids appeared only about three million years ago, with modern humans (Homo sapiens sapiens) appearing only about 90,000 years ago. If, as many paleontologists believe, birds are really proven to be dinosaurs, then we may one day say that dinosaurs have existed for almost 200 million years.

What are the two general theories as to how fast the dinosaurs went extinct?

The two general theories are catastrophism and gradualism. Catastrophism is the rapid change in conditions found on Earth, such as changes in the atmosphere, that led to the death of most species of dinosaurs. Gradualism says that the dinosaurs died out slowly, over a period of many hundreds of thousands or millions of years. This may be due, for example, to changes of climate caused by continental drift. Some scientists think both theories are correct, with all the changes coming together at the end of the Cretaceous period and leading to the extinction of the dinosaurs.

Even with all of our modern technology and medicine, diseases such as the flu (caused by the influenza virus) claim thousands of human lives each year. So it doesnt take a huge leap of the imagination to speculate that a virus or single strain of bacteria could have wiped out the dinosaurs (iStock).

What is the disease theory of dinosaur extinction?

The disease theory of dinosaur extinction (which falls under the theory of gradualism) states that dinosaurs eventually died out because of disease. Some say biological changes, brought about by changes in their evolution, made the animals less competitive with other organisms, including mammals that had just started appearing. Others say a major disease anything from rickets to constipation wiped out the dinosaurs, with some dinosaur bones definitely showing signs of these diseases over time. Another idea is that overpopulation led to the spread of major diseases among certain species of dinosaurs, and eventually to them all.

Could the atmosphere have caused the extinction of the dinosaurs?

Some scientists have proposed an atmospheric cause for the extinction of the dinosaurs. In particular, they point to a reduction in the amount of oxygen present in the atmosphere during the Cretaceous period. Researchers recently measured microscopic air bubbles trapped in amber. The study showed that the amount of oxygen present two million years before the end of the Cretaceous period was approximately 35 percent; just after the end of the Cretaceous, the amount was down to 28 percent.

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