The most widespread and accepted theory regarding the disappearance of the dinosaurs during the Cretaceous points to an asteroid that hit Earth about 66 million years ago in Chicxulub, on the coast of Mexico. Its impact, during the spring in what is now the Yucatan Peninsula, cooled the planet, darkened the sky and killed 75% of life on Earth, including non-avian dinosaurs.
Now, a team of researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences have announced they have uncovered evidence to support the hypothesis that dinosaurs were not very diverse before their extinction, that they were indeed in decline . , and generally decreased during the Cretaceous period.
The Cretaceous period we place it approximately 145 to 66 million years ago. It is the third and last period of the Mesozoic Era, as well as the longest. It is the longest geological period of the Phanerozoic, lasting approximately 79 million years.
Could they have been extinct before the impact?
Most of the scientific data on the last days of the dinosaurs comes from North America. The researchers studied more than 1,000 fossilized dinosaur eggs and eggshells (from three different species: Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis ) from the Shanyang Basin in central China. They obtained detailed estimates of the age of rock layers by analyzing and applying computer models to more than 5,500 geological samples. This allowed scientists to create a timeline of almost 2 million years to the end of the Cretaceous, with a resolution of 100-000 years, representing the period just before the extinction.
They concluded that the animals were already in decline when the asteroid hit, possibly as a result of climate change. This would have set the stage for their subsequent mass extinction.
“Our results support a long-term decline in global dinosaur biodiversity before 66 million years ago, which likely set the stage for the end-Cretaceous non-avian dinosaur mass extinction,” the authors wrote in their published study. in the journal Proceedings of the National Academy of Sciences.
While previous studies have shown that a wide range of dinosaurs were on Earth just before the asteroid hit, until now it was unclear whether they were in their prime or already on the decline.
Scientists have several theories for this
“This long-term, worldwide decline in dinosaur diversity through the end of the Cretaceous period and sustained low numbers of dinosaur lineages over the last few million years may have been the result of known global climate fluctuations and massive volcanic eruptions, i.e. “, from the Deccan traps in India . These factors may have led to ecosystem-wide instability, making non-bird dinosaurs vulnerable to mass extinction coinciding with the asteroid impact,” the researchers conclude. .
Thus, this long-term worldwide decline in dinosaur diversity through the end of the Cretaceous period and the sustained low numbers of dinosaur lineages over the last few million years could be the consequence of global climate fluctuations and massive volcanic eruptions that poison the atmosphere. All of this together would have destabilized the ecosystem, making non-avian dinosaurs vulnerable to the mass extinction that coincided with the impact of the 10-kilometre-wide asteroid and transformed the evolution of life on Earth forever.
Referencia: Low dinosaur biodiversity in central China 2 million years prior to the end-Cretaceous mass extinction. Fei Han, Qiang Wang, Huapei Wang et al. Edited by Lisa Tauxe, University of California San Diego, La Jolla, CA; received June 30, 2022; accepted July 28, 2022 September 19, 2022 Proceedings of the National Academy of Sciences 119 (39) e2211234119 DOI: https://doi.org/10.1073/pnas.2211234119