Think back to grade school, maybe even earlier, when you first heard that dinosaurs all died when an asteroid hit the earth. That’s taking things to a crazy simple level, but that idea might actually not be entirely true, according to new data published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS).

It turns out that, according to the data discovered by PNAS, dinosaurs were pretty much fading out before any such object smashed into the earth, causing widespread extinction.

“We find overwhelming support for a long-term decline across all dinosaurs and within all three dinosaurian subclades (Ornithischia, Sauropodomorpha, and Theropoda), where speciation rate slowed down through time and was ultimately exceeded by extinction rate tens of millions of years before the K-Pg boundary,” PNAS explained.

We’ll break down the science mumbo jumbo for you. The K-Pg boundary is also referred to as the Cretaceous-Paleogene boundary and is actually a strip of rock found under the surface of the earth that dates back to about 66 million years ago when scientists believe an asteroid struck the earth and ultimately killed much of the life here. That’s the stuff you’ve heard about. But this is new: PNAS is basically arguing that dinosaurs were already dying way before then. And not just croaking here and there from old age, but actually going extinct for “tens of millions of years” prior to an asteroid slammed into our home planet.

“We were not expecting this result,” University of Reading’s Dr. Manabu Sakamoto said. “While the asteroid impact is still the prime candidate for the dinosaurs’ final disappearance, it is clear that they were already past their prime in an evolutionary sense.”

“Our work is ground-breaking in that, once again, it will change our understanding of the fate of these mighty creatures. While a sudden apocalypse may have been the final nail in the coffin, something else had already been preventing dinosaurs from evolving new species as fast as old species were dying out.”

According to The Washington Post, there were some types of dinosaurs that weren’t on their way out but, thanks to the asteroid, ultimately died anyway. That includes “duck-billed dinosaurs,” which were “on the rise” when other types were giving up the ghost.

So yes, there was an asteroid, but it didn’t actually doom all dinosaurs – some of them had already packed their bags.