Long before the end of the dinosaurs was ushered by an enormous asteroid striking the Earth, they were already on a downward trend, according to new fossil records of dinosaur eggs from China.
It’s been widely accepted that a wide variety of dinosaurs were living around the world at the end of the Cretaceous period, 66 million years ago.
But scientists question whether dinosaurs were at the peak of their dominance when the asteroid struck, or if their best days had already passed.
New research published Monday in the peer-reviewed journal the Proceedings of the National Academy of Sciences seems to suggest dinosaurs were already on the decline.
A large amount of research on dinosaurs focuses on fossil records found in North America, some of which has suggested dinosaurs were thriving right before the asteroid struck, and some of which has suggested the opposite.
By looking at fossil records in China and comparing them with this existing data, researchers with the Institute of Vertebrate Palentology and Paleoanthrophy in China hoped to make a more complete picture.
They looked at more than 1,000 fossilized dinosaur eggs and fragments of eggs excavated from the Shenyang Basin in Central China.
The distinct layers of earth that different eggshells were found in allowed them to create a timeline that spanned nearly two million years at the end of the Cretaceous period, in order to examine the patterns dinosaurs were undergoing at the time.
What they found suggests that dinosaur diversity in the basin had been declining at the end of the Cretaceous period. Although they located evidence of some tyrannosaur and sauropod species, the majority of the eggs belonged to just three species. And of those three, two were from the same group of dinosaurs, a toothless species called oviraptors which, ironically, are thought to have been egg-stealers.
This low diversity was sustained across the two-million-year time period, and when researchers compared it to data from North America, they found that it collectively suggested the dinosaurs were already declining when mass extinction came for them.
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 enormous volcanic eruptions in what we now call India and other regions, destablizing global ecosystems.
