Dinosaurs were already in decline before the large asteroid that hit Earth 66 million years ago contributed to their extinction, a new study has found.
The research, published in the journal PNAS on Monday, assessed 1,000 fossilized dinosaur eggs and eggshells from the Shanyang Basin in central China and found that the dinosaurs were not very diverse before their extinction during the latter part of the Cretaceous era, about 100 to 66 million. years ago (mya).
In the study, scientists, including those from the Chinese Academy of Sciences, created a timeline of about 2 million years to the end of the Cretaceous era – the period just before the extinction of the dinosaurs. .
They found a decline in dinosaur diversity based on data from the Shanyang Basin.
Citing one example, the researchers say that the 1,000 dinosaur egg fossils collected from the basin represent just three different dinosaur species: Macroolithus yaotunensis, Elongatoolithus elongatusand Stromatoolithus pinglingensis.
Two of the three species of dinosaur eggs belong to a group of toothless dinosaurs known as oviraptors, while the other belongs to the group of plant-eating hadrosaurids, according to the study.
Tyrannosaurs and sauropods also likely lived in the area around 66.4 to 68.2 million years ago, scientists say.
Based on the analysis, the researchers say there was low diversity of dinosaur species in central China during the last 2 million years before the mass extinction.
The findings, the scientists say, suggest that dinosaurs were in decline around the world before the Cretaceous/Paleogene extinction event that wiped them out.
“Our results demonstrate low dinosaur biodiversity during the last 2 million years of the Cretaceous, and these data indicate a decline in dinosaur biodiversity millions of years before the Cretaceous/Paleogene boundary,” the scientists wrote in the study.
Researchers believe that factors such as global climate fluctuations as well as massive volcanic eruptions such as those in India’s Deccan Traps may have already led to a long-term decline in dinosaur diversity until the end of the Cretaceous. and maintained a low number of dinosaur lineages for the past million years.
These factors, they suspect, led to ecosystem-wide instability and set surviving species for mass extinction linked to the asteroid impact.
“Late Cretaceous catastrophic events, such as the Deccan Traps and bolide impact, likely acted on an already vulnerable ecosystem and led to the extinction of non-avian dinosaurs,” the scientists noted.