Mrs.Taylor Lautner
a meteor took them out

Barry C
google is your friend, but I heard OJ did it!

~Candai C~
Probably the most popular theory right now is the Asteroid Theory. According to this theory a large asteroid or comet collided with Earth about 65 million years ago. Scientists think that such a large collision would throw so much dust into the air that sunlight would not be able to shine and plants and animals would die. The dramatic changes in climate that resulted from this huge collision were too much for the dinosaurs. They were not able to survive.

Darksuga
Theory of evolution by natural selection, suggested that dinosaurs represented the remains of animals that had perished in the Biblical Flood.Most theories focused on climate change, perhaps brought on by volcanism, lowering sea level, and shifting continents.Their extinction was seen as inevitable, the product of having evolved for too long. In most extinction scenarios, the dinosaurs were simply unable to cope with competition from mammals and the changing climate, and so they all went extinct.

♥ brittany
Throughout the Mesozoic Era, individual dinosaur species were evolving and becoming extinct for various reasons. The unusually massive extinction at the end of the Cretaceous exterminated the last of the dinosaurs, the flying reptiles, and the large swimming reptiles, as well as many other marine animals. There is now widespread evidence that a meteorite impact was at least the partial cause for this extinction. Impact craters are visible on most planets in our solar system. A spectacular example of this was witnessed in 1994, when Jupiter was struck by a series of cometary fragments. Some of these impact blasts were larger than the Earth's diameter. Other factors such as extensive release of volcanic gases, climatic cooling (with related changes in ocean currents and weather patterns), sea-level change, low reproduction rates, poison gases from a comet, or changes in the Earth's orbit or magnetic field may have contributed to this extinction event.

thespeckonthebigroundthing
Bird flu