I know what you’re thinking. A massive meteorite smashed into Earth some 66 million years ago and the resulting clouds of smoke that covered the sun and sent toxic gasses into the atmosphere subsequently caused extreme climate change, i.e. the Ice Age, and all our scaly friends died in the most cataclysmic mass extinction of all time.
I’mma let you finish, but that’s only part of how it went down… according to new research, that is.
A group of UK researchers published their findings, detailing a statistical analysis of dinosaur fossil frequency over time, in Proceedings of the National Academy of Sciences. Basically, they found that dinosaurs were dying out long before that massive meteorite rocked the Earth. Apparently, this decline in dino population started 24 million years before the impact. What’s more, the dinosaurs began going extinct faster than they were speciating, meaning that new dinosaurs species weren’t evolving fast enough to replace the ones that were going extinct.
The diagram above shows the decline of several subclades of dinosaurs well before the impact. Two of the dinosaurs were actually speciating at a faster rate than then were going extinct, but they proved to be exceptions to the rule. Extinction is a natural part of life, but there’s generally a balance between extinction and speciation.
That wasn’t the case when it came to the majority of dinosaurs. I said the majority, because the Hadrosaurs lived hands of thousands of years after the meteorite impact. It should also be noted that early mammals were starting to do their thing millions of years before the impact as well.
This new evidence suggests that impact, while not the cause, was the final straw for the dinosaurs in what’s known as the “gradual decline” scenario. The group of animals were weakened by a slowed speciation process and the meteorite just finished the job. But why did they start dying off in the first place?
For starters, Earth was undergoing a massive transformation. Earth’s two supercontinents had broken apart in some Lex Luther-status catastrophe that caused sea levels to widely fluctuate. Meanwhile, megavolcanoes were erupting in India’s Deccan traps. The combination of these events, the latter of which geoscientist Gerta Keller argues spurred the extinction, caused the tropical homes of the dinosaurs to shrink. Shrinking habitats and shrinking population went hand in hand, as did an increase in population density, which left the dinosaurs vulnerable to massive extinction via a concentrated disaster.
It’s convenient to blame mass extinction on one cataclysmic event, but history has shown that mass extinctions are never so cut and dry. Mass extinction, by definition, is when 75 percent or more of Earth’s species die out, but this process usually takes over a million years. This is because it’s pretty damn hard to wipe out so many species at once and one disaster, unless it’s something insane like Superman sipping the Earth in half, won’t be enough to do the job.