Analysis of Fossil Eggs in China Adds to Debate on What Might Have Caused the Dinosaurs’ Demise | CNN

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It’s a fierce paleontological debate. Did the massive asteroid that struck Earth 66 million years ago wipe out a thriving and diverse population of dinosaurs, or were they already struggling to survive when that cataclysmic day dawned?

Most information about dinosaurs in the late Cretaceous era comes from what is now the United States, especially Hell Creek Training, which provides a picture of the relatively rich diversity of dinosaurs over the last million years of this period.

However, information about fossils from this era in other regions is much thinner, and it is unclear whether the pattern seen in North America is representative of global dinosaur diversity. then.

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

The eggs and eggshell fragments represent the last 2 million years of the dinosaur era, with fossils representing each 100,000 year interval. The study involved obtaining detailed estimates of the age of rock layers by analyzing and applying computer modeling to more than 5,500 geological samples.

The analysis found together eggs and eggshell fragments only three dinosaur species, suggesting low dinosaur biodiversity during this 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 herbivorous hadrosaur or a member of the duck-billed dinosaur group.

Researchers said their discovery from fossilized eggs was consistent with fossilized dinosaur bones found in and around the same area, although they did find a few additional dinosaur bones from the area that show tyrannosaurs and sauropods also lived in the area between 66.4 and 68.2 million years ago.

“Our results support a long-term decline in global dinosaur biodiversity before 66 million years ago,” the study states, “which likely paved the way for the mass extinction of non-avian dinosaurs from the end of the Cretaceous”.

Most dinosaurs are extinct, but some smaller, birdlike ones survived and evolved into the birds we see today.

Opponents of the asteroid sudden death theory point to a period of global cooling that may have made life difficult for many dinosaur species. Their disappearance has also been linked to a series of massive volcanic eruptions in the Deccan Traps in what is now India.

Paleontologist Alfio Alessandro Chiarenza, a postdoctoral researcher at the University of Vigo in Spain who worked on paleoclimate records from this period, said the fossilized eggs are not a reliable record of dinosaur diversity. He did not participate in the study.

He pointed to recent research that many dinosaurs probably had soft-shelled eggs that were unlikely to fossilize. Also, no eggs have been found for many dinosaurs species, even well-known as Tyrannosaurus rex, Chiarenza said.

“These findings also contradict what is apparent from egg remains and the diversity of bones, teeth and other remains found in places like Spain, (and) what we know based on northern records. -Americans,” he said via email. “So I think these authors are misinterpreting these signals.”

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

“Dinosaurs were probably beautiful and diverse and if it wasn’t for the end, the Cretaceous asteroid (they) might as well dominate today as far as we know.”

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