Chinese fossil eggs show dinosaurs’ decline before extinction

Chinese fossil eggs show dinosaurs' decline before extinction

Artist’s impression of Late Cretaceous oviraptorosaurs, hadrosaurs, and tyrannosaurs living in central China. Credit: IVPP

Nearly 66 million years ago, a large asteroid struck Earth and contributed to the global extinction of dinosaurs, leaving birds as their only living descendants.

Scientists know that at the end of the Cretaceous period, just before they became extinct, a wide variety of dinosaurs lived around the world. However, scientists have debated whether dinosaurs were at their peak before their demise or already in decline. In other words, did dinosaurs go out with a bang or a whimper?

Researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences, along with their collaborators, now have an answer. They have found evidence supporting the hypothesis that dinosaurs were not very diverse before their extinction and had declined overall during the latter part of the Cretaceous.

Their results were published in PNAS on Sept 19

Most of the scientific data In the last days the dinosaurs come from North America. Although some published studies suggest that dinosaur populations had thrived there fairly long before extinction, other more detailed research suggests that dinosaurs were instead in decline, setting the stage for their eventual mass extinction.

By examining the dinosaur records in China, the Chinese researchers hoped to determine whether this declining trend extends to Asia.

Researchers examined over 1,000 fossilized dinosaur eggs and eggshells from the Shanyang Basin in central China. These fossils come from rock sequences with a total thickness of ~150 meters. Researchers obtained detailed age estimates of the rock strata by analyzing and applying computer models to over 5,500 geological samples. This allowed scientists to create one timeline of almost 2 million years at the end of the Cretaceous – with a resolution of 100,000 years – representing the time just before the extinction. This timeline allows direct comparisons with data from around the world.

Using the data from the Shanyang Basin, the scientists identified a decline in dinosaur diversity. For example, the 1,000 dinosaur egg fossils collected from the basin represent only three different species: Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis. Also, two of the three Dinosaur Eggs oospecies come from a group of toothless dinosaurs known as oviraptors, while the other comes from the herbivorous group of hadrosaurs (aka duck-billed dinosaurs).

Some additional dinosaur bones from the region show that tyrannosaurs and sauropods also inhabited the area around 66.4 to 68.2 million years ago. This low diversity of dinosaur species was maintained in central China for the last 2 million years before the mass extinction. The small number of dinosaurs in the Shanyang Basin and central China is a far cry from the world depicted in Jurassic Park.

These results—along with data from North America—suggest that dinosaurs were likely in decline worldwide before becoming extinct.

This worldwide, long-term decline in dinosaur diversity up to the end of the Cretaceous and the continued low numbers of dinosaur lineages over the last few million years may be due to known global climate variability and massive volcanic eruptions, ie the Deccan Traps in India. These factors may have led to ecosystem-wide instability, making non-avian dinosaurs vulnerable to crowds die out coinciding with the asteroid impact.

When did dinosaurs become extinct? The theories of how it happened and what survived

More information:
Low dinosaur biodiversity in central China 2 million years before Cretaceous mass extinction, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2211234119

Citation: Chinese fossil eggs show dinosaur decline before extinction (2022, September 19) Retrieved September 20, 2022 from .html

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