Asteroid's 'bad timing' killed off dinosaurs, new evidence shows

Edinburgh University experts say asteroid hit Earth at a time when ecosystems had been weakened by a loss of biodiversity

Dinosaurs might have survived the catastrophic impact that ended their reign had the devastating asteroid that slammed into the Earth arrived at a "more convenient time", a scientist has claimed. As a result humans would probably not exist.

The violent collision 66m years ago, which occurred in the area that is now Mexico, triggered tsunamis across the oceans, caused powerful earthquakes and released enough heat to start many fires.

Material thrown into the air descended as acid rain, and also blocked the sun's warmth, cooling the Earth temporarily, perhaps by tens of degrees celsius. A thick blanket of dust that was thrown up darkened the globe, affecting plants and other photosynthesising life.

The devastation wrought by the impact almost certainly explains the sudden death of the land-based dinosaurs, according to fresh analysis of the latest data.

But one scientist on the team said the beasts might have prevailed had the asteroid struck earlier or later than it did.

Steve Brusatte, a paleontologist at Edinburgh University, was in an international team of researchers who reviewed the evidence on dinosaur extinction. The group looked at work done on prehistoric climate and temperatures, changes in sea levels, volcanic activity and biodiversity, before reaching a consensus that the asteroid was the prime culprit.

"The asteroid almost certainly did it but it just so happened to hit at a bad time when dinosaur ecosystems had been weakened by a loss of diversity," Brusatte said. "If the asteroid had hit a few million years earlier, or a few million years later, then dinosaurs probably wouldn't have gone extinct."

The scientists' report, published in Biological Reviews, found that while, largely, the dinosaurs were faring well at the time of the asteroid impact, the big plant-eating types, including the horned triceratops and duck-billed dinosaurs, had suffered a loss of biodiversity.

The loss of biodiversity in plant-eating dinosaurs left fewer animals at the bottom of the food chain for larger beasts to prey on.

"The decline made those ecosystems at the very end of the cretaceous [period], when the asteroid hit, considerably more vulnerable to collapse than those ecosystems that existed even a few million years before," said Brusatte. "There is strong reason to believe that if the asteroid had hit a few million years earlier dinosaurs would have been better able to cope."

Dinosaur biodiversity rose and fell throughout their time on Earth over 150m years. Brusatte said he suspected that given a few million years more the large plant-eaters would have recovered again, making the ecosystem more able to withstand a massive impact.

The asteroid, which had a diameter of about six miles struck the Yucatan peninsula and left a crater, now known as the Chicxulub, measuring 12 miles deep by 124 miles wide.

The collision wiped out about 80% of the Earth's species alive on Earth at the time. The non-avian dinosaurs were killed off completely, but others survived and became the direct ancestors of birds.

Though devastating for the dinosaurs, the asteroid strike cleared the way for other animals to gain ground and thrive on the planet.

"If the asteroid didn't hit, I have no reason to believe they'd have gone extinct. There is a good chance they would still be with us today. And if dinosaurs didn't go extinct, then mammals would have never had their opportunity to blossom. So if it wasn't for that asteroid, then humans probably wouldn't be here. It's as simple as that," Brusatte said.

Strong as the evidence is for the asteroid wiping out the dinosaurs, there are huge gaps in dinosaur experts' knowledge.

There is only one site, the Hell Creek rock formation in the US, spread across Wyoming, the Dakotas and Montana, that has a good fossil record covering the final years of the cretaceous period. To round out the picture of the dinosaurs' fate, far more fossils from other regions are needed.

Paul Barrett, a paleontologist and co-author of the paper, based at the Natural History Museum, in London, said: "The great dinosaur mass extinction has been one of the world's biggest mysteries and has captured the imaginations of many people. Although some types of dinosaurs were already declining in numbers before the famous asteroid impact, in most cases this impact was the smoking gun for the cause of the extinction.

"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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