Despite the common belief that the meteorite impact was the sole cause of the extinction of the dinosaurs 66 million years ago, a new study reveals that they were already in an evolutionary decline tens of millions of years before the asteroid apocalypse.
The team of researchers that conducted the study - composed of scientists from the University of Reading and the University of Bristol - used sophisticated statistical analyses in combination with information from the fossil record to reveal that the dinosaur species was not flourishing prior to the meteorite impact. Instead, they were going extinct at a faster pace than new ones were emerging as far back as 50 million years before their extinction.
The results show that the decline in species over time was seen across all dinosaur groups, although the patterns of species loss in each group varied. For example, the fastest decline was seen in the sauropod dinosaurs, whereas the theropods - which include the Tyrannosaurus rex - were declining more slowly.
"We were not expecting this result," said Manabu Sakamoto, the paleontologist from the University of Reading who led the study. "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."
"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," said Mike Benton of the University of Bristol and co-author of the research. "This was likely to have contributed to their inability to recover from the environmental crisis caused by the impact."
When the asteroid collided with Earth 66 million years ago, scientists believe that it blacked out the sun with the dust that it threw into the atmosphere, causing a short-term global cooling and loss of vegetation that spanning the globe. These events likely killed off the animals that relied on plants as well as the predators that relied on these animals for food.
The team hopes that its findings on dinosaurs can help scientists better understand biodiversity loss in the future.
"Our study strongly indicates that if a group of animals is experiencing a fast pace of extinction more so than they can replace, then they are prone to annihilation once a major catastrophe occurs," Sakamoto said. "This has huge implications for our current and future biodiversity, given the unprecedented speed at which species are going extinct owing to the ongoing human-caused climate change."
The findings were published in the April 18 issue of the Proceedings of the National Academy of Sciences.
