An artist's depiction of an approximately 6-mile-wide asteroid striking Earth.
Dinosaurs would likely still be around today if the 6.2-mile-wide Chicxulub asteroid had crashed into Earth just a little while before or after it did, concludes an international team of some of the world's leading paleontologists.
In short, dinosaurs were victims of colossal bad luck, according to University of Edinburgh vertebrate paleontologist and evolutionary biologist Stephen Brusatte, who led the study that is published in the latest issue of Biological Reviews.
"The asteroid almost certainly did it," meaning wiped out the dinosaurs, he told Discovery News, "but it just so happened to hit at a bad time when dinosaur ecosystems had been weakened by a loss of diversity."
"If the asteroid hit a few million years earlier, when dinosaurs were more diverse, or a few million years later, when they had a chance to recover as they often had done before after diversity losses, then dinosaurs probably wouldn't have gone extinct," he said.
Brusatte and his team came to this conclusion after studying an updated catalog of dinosaur fossils to create a picture of how dinosaurs, and the environment, changed over the few million years before the asteroid struck what is now Mexico.
The researchers found that during the years prior to the asteroid hit, Earth was undergoing huge volcanic eruptions and extreme changes in temperature and sea level. The changes were, at least in some respects, interconnected. For example, major volcanic eruptions, especially in what is now India, likely affected global temperatures.
Tectonic events, such as mountain formation, also led to the disappearance of a large seaway that had covered much of the interior of North America during most of the Cretaceous.
All of these changes impacted dinosaur populations, with large plant-eating dinosaurs that were at the base of the food chain particularly experiencing a dramatic drop in number. This, in turn, would have weakened the entire dino ecosystem.
Tyrannosaurus and Triceratops during the meteor strike.Joseph Tucciarone
"I think there is a perception that when the asteroid smashed into the Yucatan Peninsula 66 million years ago, it hit a static world, something of a paradise in which dinosaurs had been thriving for millions of years," Brusatte said. "But the asteroid actually hit a planet that was experiencing a lot of turmoil."
Paleontologists may be coming to a consensus on how non-avian dinosaurs--which flourished for over 150 million years--bit the dust, but they still don't know why certain birds survived the end of the Cretaceous onslaught.
"A lot of dinosaurs really looked and behaved like birds," he said. "If we were standing around in the Cretaceous, I don't think we would have made a distinction between a Velociraptor-type dinosaur and a true bird, and that is true of these feathered dinosaurs: these things were basically birds, and the line between them and birds is an arbitrary one."
Many species of birds did go extinct around 66 million years ago--just not all of them--reminded Richard Butler of the University of Birmingham's School of Geography, Earth and Environmental Sciences. Butler was not a co-author of the new paper.
Some birds might have survived because they were small, had more offspring, or possessed certain other characteristics and behaviors that permitted their survival, Butler and Brusatte theorize.
They both think that, without the asteroid impact and all of the other climatic and environmental upheaval, dinosaurs would still be roaming the planet today.
"Given that mammals were only able to expand dramatically in diversity once the dinosaurs had been extinguished, I think it is very unlikely that humans would be around today without the dinosaur extinction," Butler said.
"I think there is a very real sense in which we owe our existence to the dinosaurs' doom."