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Asteroid caught dinosaurs at weak moment, study finds

Bad timing can be deadly. The asteroid that wiped out the dinosaurs smashed into Earth during a period of environmental turmoil when the ancient food web was vulnerable to collapse, according to a new analysis in the journal Biological Reviews.

The findings, which combed through the fossil record, show that if the asteroid that hit the Yucatan in Mexico 66 million years ago had come just a few million years earlier or later, there might still be dinosaurs around today.

While the Chicxulub asteroid has been taken as the default reason for the dinosaurs’ elimination, there’s still some question as to what factors contributed to the demise of a whole group of species.

“Dinosaurs were remarkably successful for over 160 million years, evolving colossal size and diversifying into over 1,000 species distributed worldwide,” the study authors wrote.

The only direct descendants left alive are birds, which seemed to survive by taking flight. But there’s questions over whether the dinosaurs went out quickly with a proverbial bang or under longer-lasting environmental pressures.

To find out, an international team of researchers led by Stephen Brusatte of the University of Edinburgh in Scotland went through a rich catalog of dinosaur fossils (primarily from North America). By piecing that detailed timeline together, they were able to show that there were some significant environmental shifts happening in the few million years before the Chicxulub came calling.

“The latest Cretaceous world was volatile,” the study authors wrote. “Before the Chicxulub impact occurred, there were dramatic changes in sea level and temperature, as well as two phases of Deccan volcanism.”

Overall, dinosaur diversity seemed to be fine in the very late Cretaceous period, the last epoch before the extinction event. But the North American fossil record shows that the diversity of very large plant-eaters seemed to be falling. This kind of weakness in the food web could have made the communities that relied on these species more susceptible to collapse and extinction, the study authors wrote.

Call it Murphy’s law of ecology: The environmental upheaval at the time could not have killed the dinosaurs on its own – but it made them much easier to kill off when an asteroid hit. A few million years earlier, when the food web was stronger, or later, when new species could have evolved, some of them might have survived such an impact – and the world could have been a very different place.