Dinosaurs were on the decline when the asteroid hit, egg research says

Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific breakthroughs and more.


This is a tough paleontological debate. Did the giant asteroid that hit Earth 66 million years ago wipe out a thriving and diverse population of dinosaurs, or were they struggling to survive when that cataclysmic day dawned?

Most of the information on dinosaurs from the late Cretaceous period today comes from the United States, particularly from Hell Creek. training, which provides a picture of a relatively rich diversity of dinosaurs during the last million years of that period.

However, fossil information from that period is much thinner in other regions, and it is not known whether the pattern seen in North America is representative of global dinosaur diversity. then

To fill this gap in the fossil record, Chinese researchers have analyzed more than 1,000 fossilized dinosaur eggs from Shanyang. Central China basin. Dinosaur diversity was already declining at the end of the Cretaceous, the study was published on September 19 in the scientific journal Proceedings of the National Academy of Sciences.

Eggs and eggshell fragments represent the last 2 million years of the age of dinosaurs, with fossils representing each 100,000-year interval. The study involved obtaining accurate estimates of the age of rock layers by modeling and applying computer analysis of more than 5,500 geological samples.

Found analysis the whole eggs and eggshell pieces just three dinosaur species, suggesting low dinosaur biodiversity during that time period, the researchers said.

Macroolithus yaotunensis and Elongatoolithus elongatus belonged to a group of toothless dinosaurs known as oviraptors, while the third Stromatoolithus pinglingensis, was a plant-eating hadrosaur, or a member of the duck-billed dinosaur group.

The researchers he said that the discovery of fossilized eggs is consistent with fossilized dinosaur bones found in the same and nearby regions, although additional dinosaur bones were found in the region. tyrannosaurs and sauropods also lived in that area between 66.4 and 68.2 million years ago.

“Our results support a long-term decline in dinosaur biodiversity prior to 66 million years ago,” the study said, “which likely set the stage for the extinction of non-avian dinosaurs at the end of the Cretaceous.”

Most of the dinosaurs went extinct, though some smaller, bird-like ones survived and evolved into the birds we see today.

Opponents of the sudden asteroid death theory point to a period of global cooling that could have made life difficult for many species of dinosaurs. Their extinction has also been linked to massive volcanic eruptions in the Deccan Traps, which is now India.

Paleontologist Alfio Alessandro Chiarenza, a The post-doctoral researcher at the University of Vigo in Spain, who has worked on paleoclimate records from that time, said they are fossilized eggs. is not a reliable record of dinosaur diversity. He did not participate in the study.

In recent research, he noted that many dinosaurs probably had soft-shelled eggs that would not have fossilized. Also, no eggs have been found for many dinosaurs species, even well-known ones like Tyrannosaurus rex, Chiarenza said.

“These results also contradict what we know from egg remains and the diversity of bones, teeth and other remains found in places like Spain, (and) based on the North American record,” he said by email. “So I think these authors are misinterpreting those signals.”

He remains convinced that the asteroid strike was the real driver of the extinction of the dinosaurs.

“Dinosaurs were probably fine and varied, and if it weren’t for the late Cretaceous asteroid (they) would have dominated as we know it today.”