It’s turning toward spring here in North America, and a few bulbs are doing their best to bud through the mud and snow enjoyed by a lot of our team. Spring: It’s a time for renewal, for birth, and, according to new research appearing in Nature, spring is a time for mass extinction.

Scientists are continuing to learn everything they can about arguably the worst day in Earth’s history – the day the dinosaurs died. And this new science result started off a little strange – that day was in the springtime. No, really. That is the result of this research, which was published last week and led by vertebrate paleontologist Melanie During.

Scientists studying sedimentary rocks and fossils at the amazing Tanis site in southwestern North Dakota analyzed the bones of paddlefish and sturgeons to try and determine what time of year the Chicxulub impact occurred. Today I learned that fishbones, like trees, contain the marks of cyclical evidence for growth patterns. Vigorous growth shows up as thick bands, while slower growth makes for thinner bands, and times of drought or famine show up as a line of arrested growth. Those lines can also designate wintertime food cycles.

And lead author During explained that the fossilized fish in this study turned out to be growing just fine at the time of their demise; however, they had not yet reached the peak of their growth cycle which tends to occur in summer. The lines of arrested growth came at regular intervals, and these fish weren’t in one of those periods based on the banding. The conclusion reached is that the fish all died in the springtime.

So how does this relate back to the Chicxulub impact and the end of the dinosaurs? The fish fossils at the Tanis site are known to have been found with tiny spherules of solidified molten rock stuck in their gills. This means the fish were still alive when the impact’s effects rained fire and molten rock on them, killing them close to the time of the impact.

And now for the why the season is important. We want to understand not just how and why the dinosaurs disappeared from the fossil record but also why smaller mammals and birds and such may have survived. If it was springtime in the Northern Hemisphere, that means many of those small creatures would have been fresh out of hibernation and out seeking food. But in the Southern Hemisphere, it would have been autumn, and the same types of creatures would have been setting up their burrows and hiding underground, possibly even protected from the literal fallout of the impact. That could have given them a better chance for survival.

Obviously, something saved the smaller birds and mammals so that they could evolve into what we have today, which is no dinosaurs. Except for the chickens.

More Information

The Age of Dinosaurs may have ended in springtime (Science News)

“The Mesozoic terminated in boreal spring,” Melanie A. D. During et a., 2022 February 23, Nature