A common theory holds that dinosaurs were eradicated by the fallout from an asteroid that collided with Earth. But new research says they were already in decline for millions of years when the meteor finished them off.
A gradual reduction in the number of dinosaur species may explain what made them unable to recover in the wake of the meteor impact, and it may hold insight for the importance of biodiversity as a defense against apocalyptic events.
Combining fossil evidence with statistics, a team of researchers at two British universities found that dinosaur species were already at the tail end of their long period as dominant species on Earth when the blast came. The team published its findings Monday in the Proceedings of the National Academy of Sciences.
"Our study strongly indicates that if a group of animals is experiencing a fast pace of extinction more so than they can replace, then they are prone to annihilation once a major catastrophe occurs," co-author Manabu Sakamoto of the University of Reading said in a press release. "This has huge implications for our current and future biodiversity, given the unprecedented speed at which species are going extinct owing to the ongoing human-caused climate change."
The last of the dinosaurs died out about 66 million years ago, after a large meteor struck the Yucatan Peninsula in Mexico near where the town of Chixculub stands today. The so-named Chixculub impactor left a crater 110 miles wide and, among other effects, would have filled the air with enough dust to block the sun that would cause the planet to cool, creating massive plant and animal die-offs.
But the researchers found through the study of "phylogenetic trees" — records of the various species of dinosaur and how they are related to each other — that the diversity of dinosaur species was already shrinking well before the meteor strike.
"All the evidence shows that the dinosaurs, which had already been around, dominating terrestrial ecosystems for 150 million years, somehow lost the ability to speciate fast enough," co-author Mike Benton of the University of Bristol said in a press release. "This was likely to have contributed to their inability to recover from the environmental crisis caused by the impact."
Essentially what that means is that dinosaur species were dying out faster than new species could replace them.
The researchers could not identify the specific causes that made it harder for dinosaur species to continue propagating. It could have been geological changes, such as the breakup of the super-continents Gondwana and Laurasia, or volcanic eruptions around the world. Those events coincided with that time period.