Long before the end of the dinosaurs was ushered in by a huge asteroid hitting Earth, they were already on a downward trend, according to new fossil records of dinosaur eggs from China.
It is widely believed that a wide variety of dinosaurs lived around the world during the late Cretaceous, 66 million years ago.
But scientists wonder if the dinosaurs were at the height of their dominance when the asteroid hit, or if their best days had already passed.
New research published Monday in the peer-reviewed journal Proceedings of the National Academy of Sciences seems to suggest that dinosaurs were already in decline.
Much dinosaur research focuses on fossil records found in North America, some of which have suggested dinosaurs thrived just before the asteroid hit, and some of which have suggested otherwise.
By examining the fossil record in China and comparing it to this existing data, researchers at the Institute of Palentology and Paleoanthropy of Vertebrates in China hoped to paint a more complete picture.
They examined more than 1,000 fossilized dinosaur eggs and egg fragments excavated from the Shenyang Basin in central China.
The different layers of earth in which different eggshells were found allowed them to create a timeline that spanned almost two million years to the end of the Cretaceous, to examine the patterns that dinosaurs underwent. at the time.
What they found suggests that the diversity of dinosaurs in the basin had declined by the end of the Cretaceous. Although they found evidence of some tyrannosaur and sauropod species, the majority of the eggs belonged to just three species. And of these three, two belonged to the same group of dinosaurs, a toothless species called oviraptors which, ironically, were said to be egg thieves.
This low diversity was maintained throughout the two-million-year period, and when the researchers compared it to data from North America, they found it collectively suggested that dinosaurs were already in decline. when mass extinction arrived for them.
The researchers say further study is needed to determine the causes of this decline, but they believe it could be due to global climate fluctuations and huge volcanic eruptions in what we now call India and other regions. , destabilizing global ecosystems.