The following questions were answered by dinosaur expert Don Lessem, paleontologist Tim Rowe, and paleontologist Bill Hammer.


Q: In what year did the dinosaurs die?
A: The last dinosaurs are known from about 65 million years ago, but we don't know the exact date. (Don Lessem)


Q: Did all of the dinosaurs die at the same time? If not, how many years did it take for the dinosaurs to die out?
A: All dinosaurs did not die at the same time. There are 335 kinds known so far from 165 million years, and no one kind lived for more than two million years or so. The only reason we think of dinosaurs as going extinct at one time, 65 million years ago, is that this last group of dinosaurs didn't get replaced later on by another group of dinosaurs as had happened before. (Don Lessem)


Q: Why didn't all plants and animals die when the dinosaurs died?
A: Great question! Most animals and plants did die out with dinosaurs, just as they did about five other times when there were huge disasters in the billions of years of earth history. That's not very often, so I wouldn't worry about it happening while we are around. We don't know why any of this happened, so we don't know why it didn't destroy all living things. There was probably a big weather change, from volcanoes or asteroids changing the climate. Some animals and plants that were tough, or little, could survive even these big changes in weather. I'm just glad all plants and animals didn't die out with the dinosaurs, or there would be no us. (Don Lessem)


Q: Why did dinosaurs become extinct? Could you tell us about the nemesis theory of why dinosaurs disappeared? What about the impact theory?
A: The nemesis theory is one of many "It came from outer space" theories of dinosaur extinction. The idea is that a comet comes close to the earth every 26 million years and brings with it lots of debris that hits the planet, changes the weather and kills off lots of animals. 65 million years ago it might have killed off dinosaurs, pterosaurs and big marine reptiles. A related theory, that asteroids cause extinctions, has evidence in a big asteroid crater found lately in Mexico from 65 million years ago. But we don't know if that was enough to do in the dinosaurs or if it happened after the dinosaurs were already on the way out or entirely gone. The truth is, we don't what caused dinosaur extinction and it might have been a combination of things like asteroids, volcanoes, gradual climate changes, and even disease. It's a mystery! (Don Lessem)

Dinosaurs became extinct at the end of the Cretaceous period, approximately 65 million years ago. While some scientists think a large asteroid killed off the dinosaurs (also known as the impact theory), many paleontologists feel that climate change due to a drop in sea level might have been responsible. I think the extinction question is still unresolved, but I am not a strong believer in the impact theory. (Bill Hammer)

I really don't know. What makes you so sure that dinosaurs really are extinct? Seems like everyone wants to know why dinosaurs went extinct. But there is a group of scientists who seriously argue that not all dinosaurs went extinct 65 million years ago. Of course triceratops and T. rex did die out. But there is also a lot of evidence to suggest that modern birds evolved from the carnivorous theropod dinosaurs. If this is true, if dinosaurs have living descendants, is it entirely fair to say that the dinosaurs are extinct? The latest news flashes from the journal Science point to volcanic eruption as an important mechanism in mass extinctions. One group of scientists has discovered that there was a huge episode of eruption in what is now Siberia at the beginning of the Mesozoic — a time in earth's history when there was an extinction even greater than the one at the end of the Mesozoic that killed many of the dinosaurs. A second group of scientists has looked at the recent death of some coral reefs and discovered that volcanic dust from an eruption far away was responsible. This doesn't necessarily mean that the extinction at the end of the Cretaceous was in fact caused by volcanic eruptions, but it makes that idea a lot stronger. (Tim Rowe)


Q: I heard an interesting theory concerning dinosaur extinction. I once heard a scientist say he thought dinosaurs did not "die out" but instead they evolved into today's reptiles and birds. What do you think of that one?
A: Many scientists think birds are dinosaurs. Certainly, it appears that birds are descended from meat-eating dinosaurs and the earliest birds look just the same — except for feather impressions — as small meat-eating dinosaurs. It's a question of semantics, then, whether birds are living dinosaurs or their closest living relatives. (Don Lessem)


Q: I heard a scientist theorize that the dinosaurs simply died of disease because they were somewhat nomadic. They would move to a new area and get exposed to germs that their immune systems could not fight. Is this true? He also implied that the continents were not fully separated, as they are today.
A: A reasonable idea, this disease business, but hard to prove. Continents came apart in the Age of Dinosaurs, then reunited near the end of it, with North America, Asia, and South America joined. I don't know if the dinosaurs needed to be so nomadic; even the little mammals could have brought the diseases. (Don Lessem)