Why dinosaurs become extinct? Because they had bad luck.

"Dinosaurs were the victims of a colossal bad luck," says a paleontologist, Dr. Steve Brusatte of the University of Edinburgh. Their disappearance would not only be due to the collision of Earth with a giant asteroid, but a combination of factors, which were combined in the most unfortunate for these creatures.

If the asteroid that gave the blow would come a little earlier or a little later in Earth history, dinosaurs could have survived. "Misfortune" them, says Dr. Brusatte, is that they had a large number of problems in a short time.

When the 10 km diameter asteroid struck the Earth now about 66 million years ago, dinosaurs were already vulnerable because of a series of events that had a negative impact on them.

Intense volcanic activity, changing sea water level and temperature fluctuations already had weakened food chains which included dinosaurs.

If the asteroid had hit a few million years earlier when species diversity was greater and more solid food chains, dinosaurs could have survived. Also, if the impact had occurred a few million years later, when it already evolved new species, this group of animals would be able to survive extinction, shows an international, published in the journal Biological Reviews.

But the asteroid "hit the most inopportune moment, when ecosystems which included dinosaurs were vulnerable," says Brusatte. Fall asteroid caused earthquakes, tsunamis, wild fires, sudden temperature fluctuations and other environmental changes that dinosaurs could not cope and destruction herbivorous dinosaurs that are the basis of food chains affected the species that feed on them. As a result, almost the entire group of dinosaurs disappeared. New study shows that "extinction was abrupt," says Dr. Brusatte; took place in a short time, a few tens or hundreds of thousands of years, slowly over millions of years, as claimed by other palentologi.

The only species in this group survived were those that evolve in today's bird. The research was performed predominant on dinosaur fossils in North America; remains as future studies may show whether these explanations are valid for dinosaurs in other parts of the world.