The mass extinction of the dinosaurs, after an asteroid struck Earth some 66 million years ago, was a tumultuous end to the reign of these once-dominant animals. But now a new study suggests that they were already disappearing millions of years before the meteorite impact.
“Dinosaurs gradually went extinct over millions of years,” study author Qiang Wang told the South China Morning Post.
+ Asteroid or volcanoes? Scientists challenge dinosaur theory
However, the investigator hopes that these conclusions will be tested. The study builds on a long-standing debate among paleontologists over whether the dinosaurs came to an abrupt end or were already on the brink of extinction before a 10-kilometer-wide asteroid called Chicxulub sealed their fate.
New research by a team of geologists and paleontologists working in China suggests that dinosaur biodiversity was disappearing at least two million years before their extinction in the late Cretaceous, leaving birds as their only living descendants.
Their conclusions are based on a collection of egg fossils, including several complete and incomplete dinosaur eggs, preserved in 150-meter-thick layers of rock that were deposited between 68.2 and 66.4 million years ago, even before the curtain fall on the dinosaurs.
“Our results support a long-term decline in global dinosaur biodiversity before 66 million years ago”
“Our results support a long-term decline in global dinosaur biodiversity before 66 million years ago, which likely set the stage for the mass extinction of non-Asian dinosaurs,” the University of California researcher explained. China Geosciences, Fei Han and colleagues.
In their work, Han and his colleagues used a set of techniques to stratify thousands of rock samples encapsulated in fossilized eggshells, estimate the age of those samples, and build a timeline with these data at 100,000-year resolution.
Two of the three dinosaur eggs in a species category when you have only eggs identified in the mix were from a group of toothless, parrot-like dinosaurs called oviraptors, with the third group of laying dinosaurs being identified as duck-billed hadrosaurids.
The low species diversity the researchers found matches skeletal remains of ancient dinosaurs also discovered in the Shanyang Basin, and is comparable to other fossil deposits in southern and eastern China, as well as some bone beds in North America that also suggest the decline in dinosaur diversity. during the same period.
Dinosaur decline “may have resulted from global climate fluctuations and volcanic eruptions”
All “point to lower diversity and global decline among dinosaurs on a global scale,” argue Han and colleagues, suggesting that the decline may have resulted from global climate fluctuations and volcanic eruptions.
Other studies, which also suggested that dinosaurs were prone to extinction, have suggested that their diversity may have started to decline up to 10 million years before the meteorite hit Earth.
However, previous studies have found the opposite. A recent, comprehensive analysis simulating dinosaur speciation – the rate at which new species appear – found that less than 20% of dinosaurs were in terminal decline before the asteroid impact, while other species were thriving.
The only way to resolve these conflicting interpretations, conclude Han and colleagues, is to find, sample and analyze more fossils and integrate existing data from fossil sites around the world to better understand patterns of extinction.
It’s certainly not an easy task, but one that might help to finally sort out what happened in light of the decline of the dinosaurs’ reign.
“Our study in Asia of abundant and geochronologically dated fossils is an important step in this direction,” the researchers write.
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