Even though the Chicxulub asteroid impact struck the final blow some 66 million years ago, the dinosaurs were experiencing an evolutionary decline tens of millions of years prior to that event, claims new research published in the Proceedings of the National Academy of Sciences.
Using an in-depth statistical analysis along with data from the fossil record, scientists at Bristol University and the University of Reading in the UK discovered that dinosaur species were going extinct at a much quicker pace than new ones were emerging from about 50 million years before the fateful meteorite hit the Earth’s surface in what is now Mexico’s Yucatan Peninsula.
The new discovery runs contrary to the previous notion that dinosaurs had been thriving right up until the moment of impact and reveals that species experienced their own pattern of decline, the study authors explained in a statement. For instance, long-necked giant sauropods underwent the fastest decline, while theropods experienced a slower, more systematic one.
“We were not expecting this result,” said lead author Dr. Manabu Sakamoto, the University of Reading paleontologist who lead the investigation. “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.”
Long the planet’s dominant species, they were already slowly fading away
According to BBC News and the Los Angeles Times, Dr. Sakamoto and his colleagues studied dinosaur fossils from the moment they emerged 231 million years ago until the time they went extinct, and found that the evolution of new species began to slow about 160 million years ago. By 120 million years ago, the slow decline in the number of species had begun.
With fewer species of dinosaurs, as well as less variation in habitat requirements, the creatures would have gradually become increasingly susceptible to environmental change, the researchers explained in their study. Even without the asteroid impact that eventually finished them off, the dinosaurs probably would have died off naturally, Dr. Sakamoto and Chris Venditti, co-author of the study and a biology professor at the university, told the Times via email.
“Our work is ground-breaking in that, once again, it will change our understanding of the fate of these mighty creatures,” Dr. Sakamoto explained in a statement. “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. This suggests that for tens of millions of years before their ultimate demise, dinosaurs were beginning to lose their edge as the dominant species on Earth.”
“All the evidence shows that the dinosaurs, which had already been around, dominating terrestrial ecosystems for 150 million years, somehow lost the ability to speciate fast enough,” added University of Bristol Professor Mike Benton, also one of the paper’s co-authors. “This was likely to have contributed to their inability to recover from the environmental crisis caused by the impact.”
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