Blame a brutal case of spring cleaning for wiping the dinosaurs off the face of the Earth. Well, the actual cause of death is the asteroid that catapulted towards Earth 66 million years ago. The singular incident, which struck down at the location of modern day Yucatán peninsula, effectively ended the Cretaceous Period, wiping out a baffling three-quarters of Earth’s species. Chief among them, the non-avian dinosaurs; so your Brontosaurus, Tyrannosaurus rex, and the pesky Velociraptor. But scientists studying ancient fish fossils have narrowed down the time of death to a single season. The mass extinction event occurred, more specifically, in the spring.
A team of scientists from universities in The Netherlands, Sweden, Belgium, and France published their findings in Nature. Specifically, the team studied the fossils of fish located at a site in North Dakota called Tanis. Notably, the fish died in the immediate aftermath. (We first saw this at Science.)
The paper’s lead author, Melanie During, a researcher from Uppsala University and the VU Amsterdam, explained it in a press release. She says how imperative it was to have the fish to learn more about the exact moment of impact. The team used a particle accelerator which the press release notes “produces the world’s brightest x-rays” on samples from the fossilized fish. They also did “high-resolution synchrotron X-ray tomography” as part of their research.
Dennis Voeten, researcher at Uppsala University and author on the paper, explain scientists can trace bone cell density and volumes in the fish. “They indicate, he said, “whether it was spring, summer, autumn, or winter. We saw that both cell density and volumes were on the rise but had not yet peaked during the year of death, which implies that growth abruptly stopped [in the] spring.”
During, the paper’s lead author, told Science that the incident occurring during the spring was a particularly brutal time. Similarly to animals now, the dinos would’ve hibernated through the winter and spent their spring roaming the wilds and mating. So the creatures roaming the prehistoric Tanis spot were certainly sitting ducks on that doomed spring day. The springtime-specific findings are pretty monumental on their own. But it is just the beginning of the research into why some animals survived the deadly explosion—how the Northern Hemisphere’s mass extinction fared against those in the Southern Hemisphere. Plus hibernation’s role in the whole ordeal.