Dinosaur Population and Diversity Had Hit Rock Bottom Much Before the Extinction-Triggering Asteroid Struck Earth: Study


Artist's depiction of Late Cretaceous oviraptorosaurs, hadrosaurs, and tyrannosaurs living in central China (Credits: IVPP)

Artist’s depiction of Late Cretaceous oviraptorosaurs, hadrosaurs, and tyrannosaurs living in central China

(Credits: IVPP)

The asteroid that slammed into the Earth’s surface around 66 million years ago carries the tag of wiping 75% of Earth’s life forms, including the dinosaur species. But now, scientists have suggested that even if history (and that one fateful asteroid) had changed its course, the extinction of dinosaurs was probably inevitable.

Previously, studies have played the devil’s advocate by hypothesizing that climate change and volcanic eruption had led dinosaur numbers to reach their rock bottom around 75 million years ago — much before the space rock crash-landed on Earth.

Now, a new study conducted by researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences has further suggested that not only did the dinosaur numbers dwindle, but their species diversity was itself quite limited, which anyway got them to the brink of extinction.

To arrive at this conclusion, the scientists examined over 1,000 fossilized dinosaur eggs and eggshells found across 150-metre-thick rock layers from the Shanyang Basin in central China. These rocks were from the final 2 million years of the Cretaceous period — the phase just before the mass extinction.

Out of all the egg samples analyzed, they found only three distinctive species of dinosaurs — Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis. Two of them belonged to the class of toothless dinosaurs known as oviraptors, while the third was a herbivorous duck-billed dinosaur.

Additionally, they found a few tyrannosaur and sauropod bones — the creatures that lived somewhere between 66.4 and 68.2 million years ago. But overall, this sparse variety showed a clear plunge in biodiversity compared to older fossil records.

According to scientists, the global climate instability and the volcanic eruptions in the Deccan Traps of India shrunk the diversity and few dinosaur lineages at the end of the Mesozoic Era (252 to 66 million years ago). And since the remaining dinosaurs eventually lost the ability to adapt and recover from sudden environmental changes, they saw a global decline and became even more vulnerable to the mass extinction that took place because of the 10km-wide asteroid strike in Mexico.

“Dinosaurs went extinct gradually over millions of years, instead of coming to an abrupt end from sudden disasters,” explained lead author Wang Qiang in an interview with China’s local daily.

The results of this study provide a further scope to assess the ultimate cause of the loss of adaptability that made them vulnerable to extinction. Did modification in their genes contribute to the loss of adaptability, or was it just the environment that became too harsh for them?

This research was published in the journal PNAS on Friday, September 19, and can be accessed here


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