Image copyright SPL Image caption Could dinosaurs have survived if the asteroid that wiped them out hit the Earth a little earlier or a little later?

Dinosaurs were wiped out by an asteroid impact when they were at their most vulnerable, according to a new study.

Dr Steve Brusatte, of Edinburgh University, said sea level rises and volcanic activity had made many species more susceptible to extinction.

They might have survived if the asteroid had hit the Earth a few million years later or earlier, he said, calling it "colossal bad luck".

The assessment has been published in the journal, Biological Reviews.

"It was a perfect storm of events that occurred when dinosaurs were at their most vulnerable," Dr Brusatte told BBC News.

With evolution never say never. It is certainly possible that dinosaurs could have evolved intelligence Dr Steve Brusatte, Edinburgh University

The study brought together 11 leading dinosaur experts from the UK, US and Canada to assess the latest research on the extinction of dinosaurs 66 million years ago.

There is evidence that some species of dinosaur were dying off shortly before an asteroid hit the Earth.

One of the key questions was whether this gradual decline would have led to the extinction of these animals even if the asteroid had not hit.

The experts concluded that although some species of plant eaters in North America were dying out in the period leading up to the asteroid impact there was no evidence of a long-term decline.

However, the experts believe that rises in sea level and increased volcanic activity made many species more susceptible to extinction just at the point that the asteroid struck.

Them or us?

Dr Brusatte believes that had the asteroid hit the Earth a few million years earlier before the environmental pressures became worse or a few million years later, when the dinosaurs might have recovered, they would be roaming the Earth to this day.

"Five million years earlier dinosaur ecosystems were much stronger, they were more diverse, the base of the food chain was more robust and it was harder to knock out a lot of species," he said.

"If they had a few million years more to recover their diversity they would have had a better chance of surviving the asteroid impact. Dinosaurs had been around for 160 million years, they had plenty of dips and troughs in their diversity but they always recovered."

It was the demise of the dinosaurs that enabled mammals including our own species to diversify and evolve.

Dr Brusatte said that if it were it not for an asteroid hitting the Earth exactly when it did we would be living in a dinosaur dominated world.

Image copyright Thinkstock Image caption We could all be living in a dinosaur world today, except there would be no "we".

"Except that we would not be here because mammals would not have had the opportunity to blossom and we would not be having this conversation!" he quipped.

This intriguing idea raises the question as to how dinosaurs might have evolved.

Could they have developed in the same way as mammals, becoming an advanced species similar to modern humans?

I asked Dr Brusatte: "Could dinosaur you and dinosaur me be having this conversation, instead?"

We can't re-run the tape of life and see whether an impact at a different time would have led to total extinction - but it did come at a particularly bad time Dr Richard Butler, Birmingham University

"It's possible!" he said. "With evolution never say never. It is certainly possible that dinosaurs could have evolved intelligence."

Professor Simon Conway-Morris from the University of Cambridge agrees, but does not go quite as far as Dr Brusatte.

"As far as dinosaurs becoming intelligent is concerned the experiment has been done and we call them crows," he told BBC News.

Advanced intelligence

He adds that if there was no mass extinction then he believes that the dinosaurs would not have carried on to the present day.

He says that other groups of animals were more likely to have developed advanced intelligence and the ability to make tools.

"From that moment the dinosaurs would have been toast," he said.

Others involved in the study are less bullish than Dr Brusatte. They say that while his arguments are plausible they believe that it is impossible to say whether dinosaurs would have survived had the asteroid hit the Earth at a slightly different time.

"We can't re-run the tape of life and see whether an impact at a different time would have led to total extinction," says Dr Richard Butler from Birmingham University.

"But it did come at a particularly bad time."

Dr Paul Barrett of the Natural History Museum says that the new study shows that types of dinosaurs were already declining in numbers before the asteroid impact.

"This new work provides the best evidence for sudden dinosaur extinction and for tying this event to the asteroid impact rather than other possible causes such as the longer-term effects of the extensive volcanic activity that occurred at the end of the Cretaceous."

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