The researchers analyzed the shells of lizard eggs.
Chinese scientists said that dinosaurs were already on on the way to extinction even before the impact of the asteroid that is believed to have led to their demise. The researchers came to these conclusions after analyzing the shells of 1,000 fossilized eggs, reports Science alert.
The reasons for the death of dinosaurs have been of interest to scientists for a long time. They are thought to have become extinct after an asteroid hit Earth, followed by massive volcanic eruptions and a change in global temperature. It happened about 66 million years ago.
Read also: Not an asteroid: scientists named the cause of the death of dinosaurs
Currently, scientists have come up with a new assumption, which, however, needs to be confirmed. The results of the scientists' study showed that the dinosaurs were extinct for two million years before the asteroid hit.
Researchers studied fossilized eggshells laid between 68.2 and 66.4 million years ago, shortly before the end of the era of dinosaurs. The Shanyang Basin, where the eggs were discovered, is also one of the largest sources of dinosaur fossils. Despite this, scientists have found eggshells of only three taxa of these animals, which indicates a reduction in their biodiversity compared to earlier eras.
Scientists believe that this change in biodiversity may have reduced the dinosaurs' collective ability to recover from the impact of the asteroid. According to them, “the decline in biodiversity set the stage for the extinction of non-avian dinosaurs at the end of the Cretaceous period.”
During the study, scientists used a set of methods to stratify thousands of rock samples that contained fossilized shells, estimate the age of these samples and construction of a time scale with a resolution of 100 thousand years.
Two of the three eggs belonged to oviraptors – toothless, parrot-like dinosaurs. A third group of dinosaurs has been identified as herbivorous “platy-nosed” hadrosaurids. This low biodiversity in egg samples also corresponds to the remains of adults found in this region. In addition, a reduction in the number of represented species is also indicated by some excavations conducted in North America.
Scientists believe that this “indicates a decrease in diversity and a general reduction in the number of dinosaurs on a global scale.” This was probably due to volcanic eruptions and global climate change.
Other studies, the results of which also suggest a slow extinction of the dinosaurs before the impact of the asteroid, say that this process could have started 10 million years before disasters.
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But other studies suggest otherwise. For example, a recent analysis of dinosaur biodiversity showed that only 20% of species were in decline before the fall, while others thrived.
