When Tim, the nine-year-old kid in Jurassic Park, listed a bunch of ways the dinosaurs might have died, a meteor was the most appealing—it's quick, and clean, and doesn't involve the coolest animals that ever lived suffering slowly from a horrible plague or something. And while we're now more-or-less positive a meteor collided with Earth near the Yucatán Peninsula and created the Chicxulub crater, triggering a mass die off of many of Earth's species, it turns out their deaths weren't exactly swift.
According to a new study just published in the Proceedings of the National Academy of Sciences, the dinosaurs had been in an an evolutionary tailspin for millions of years by the time of that mass extinction. Species had been dying off, and new species weren't showing up to replace them. Less dinosaur biodiversity would have made dinosaurs on the whole more susceptible to a disaster like, say, a giant meteor.
It's not an entirely new idea. A study in 2012 found that changes in "morphological disparity"—the amount of physical difference between dinosaurs—may have indicated a pre-meteor decline. However, the authors of this study, based at the University of Reading in England, say they took a "statistical approach," looking at a family tree–like diagram of dinosaur species over time, and creating a mathematical model for species changes, resulting in greater certainty that dinosaurs were dying en masse before that meteor came.
"There is no doubt that the Chicxulub impact was the final nail in the dinosaurs' coffin—with the exception of birds," one of the authors, Manabu Sakamoto, told the Los Angeles Times. However, Sakamoto explained, even if the Earth had whiffed past that meteor like a drunk batter missing a curveball, the dinosaurs may well have gone extinct on their own.
The paper speculates about the possible culprits causing long-term dino decline. The Cretaceous period was a generally shitty time to be a dinosaur: Continental drift was separating the continents, and other massive geological changes were contributing to a rise in volcanic eruptions. Plus, Earth was cooling off.
But Sakamoto would hate for you to get the wrong idea about the hazards of a cooling Earth as opposed to a warmer one. "We are putting a lot of pressure on modern species, and extinctions are happening at an unprecedented rate," he told Ed Yong at the Atlantic. "If some kind of catastrophe occurs, it might be even more damaging than what we're observing right now."
Follow Mike on Twitter.