Chinese Fossil Eggs Show Dinosaur Decline Before Extinction

Chinese Fossil Eggs Show Dinosaur Decline Before Extinction

Artist’s depiction 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 the dinosaurs, leaving birds as the only living descendants.

Scientists know that a wide variety of dinosaurs lived around the world during the late Cretaceous just before their extinction. However, scientists have wondered if the dinosaurs were at their zenith or already in decline before their demise. In other words, did the dinosaurs come out with a bang or a groan?

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 found evidence to support the hypothesis that dinosaurs were not very diverse before their extinction and declined overall during the later part of the Cretaceous.

Their findings were published in PNAS September 19.

Most of the scientific data on the last days of the dinosaurs comes from North America. Although some published studies suggest that dinosaur populations were thriving quite well before the extinction, other more detailed research has suggested that the dinosaurs were on the decline, which set the stage for their eventual mass extinction.

By examining dinosaur records in China, Chinese researchers hoped to determine whether this downward trend also extended to Asia.

Researchers studied more than 1,000 fossilized dinosaur eggs and eggshells from the Shanyang Basin in central China. These fossils came from rock sequences with a total thickness of about 150 meters. The researchers obtained detailed estimates of the age of the rock layers by analyzing and applying computer modeling to more than 5,500 geological samples. This allowed scientists to create a timeline of almost 2 million years at the end of the Cretaceous – with a resolution of 100,000 years – representing the period just before extinction. This timeline allows for direct comparisons with data from around the world.

Scientists have identified a decline in dinosaur diversity based on data from the Shanyang Basin. For example, the 1,000 dinosaur egg fossils collected from the basin represent only three different species: Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis. Additionally, two of the three oospecies of dinosaur eggs belong to a group of toothless dinosaurs called oviraptors, while the other belongs to the group of plant-eating hadrosaurids (also called duck-billed dinosaurs).

A few additional dinosaur bones from the area show that tyrannosaurs and sauropods also lived in 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, together with data from North America, suggest that dinosaurs were likely in global decline before their extinction.

This long-term global decline in dinosaur diversity until the end of the Cretaceous and the low number of dinosaur lineages over the past few million years may be the result of known global climatic fluctuations and massive volcanic eruptions, i.e. Deccan traps in India. These factors may have led to ecosystem-wide instability, thus making non-avian dinosaurs vulnerable to mass extinction coinciding with the asteroid impact.


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

Provided by Chinese Academy of Sciences

Quote: Chinese fossil eggs show pre-extinction dinosaur decline (September 19, 2022) Retrieved September 20, 2022 from https://phys.org/news/2022-09-chinese-fossil-eggs-dinosaur-decline.html

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