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Life on planet Earth is a fragile thing. All you need is a wayward asteroid, and bam, here’s the most dominant group of land animals on our planet.
Had it not been for the 10-kilometer-wide meteorite that crashed to Earth some 66 million years ago, dinosaurs could have continued to dominate the earth, a new document suggests. As for mammals like us, we may never have had a chance to be resurrected.
The findings are the latest in a long and drawn-out debate on the extinction of non-avian dinosaurs.
While the asteroid Chicxulub and the aftermath of its impact – which blocked the sun’s rays and triggered the cooling of the global climate – are generally considered prime candidates for the massive Cretaceous extinction event, some recent evidence suggests that some species of dinosaurs were already in decline tens of millions of years earlier.
The authors of these findings claimed “overwhelming support for a long-term decline in all dinosaurs and within all three major dinosaur groups,” but among paleontologists, support for this idea is by no means overwhelming. . Indeed, it is extremely controversial.
In the years since this idea was first put forward, many other lines of research have disagreed with his conclusions, not necessarily with the data themselves, but with the interpretations drawn.
Gaps in dinosaur fossils and sampling errors indicate that we may be under sampling some Cretaceous dinosaurs, overstating the presence of others.
“Previous studies by others have used various methods to draw the conclusion that dinosaurs would still go extinct, as they were in decline towards the end of the Cretaceous period,” explains paleontologist Joe Bonsor of the University of Bath.
“However, we show that if you expand the dataset to include newer dinosaur family trees and a wider range of dinosaur types, the results don’t really all point to this conclusion, in fact only about half of them do. “.
Rather than simply counting the number of dinosaur species present at that time using the fossil record, the team used statistical methods to examine the speciation rate within dinosaur families.
By analyzing thousands of combinations of family trees in 12 dinosaur families, the researchers tested whether species diversification was slowing down, staying unchanged, or accelerating before the asteroid impact, an indication that could tell us how quickly extinct dinosaurs are being replaced. with new dinosaurs.
Of all 2,727 speciation models, only 518 (less than 20%) unequivocally showed a terminal decline before the asteroid impact.
Even when the authors considered those on the border between terminal decline and no decline, that’s just over half of the models that would support a more prolonged extinction.
Therefore, the team says they are skeptical of the terminal extinction theory, suggesting instead that dinosaur diversity would have remained high during the late Creataceous, even though species richness varied between branches.
“The main point of our article is that it is not as simple as looking at some trees and making a decision. The big inevitable bias in the fossil record and lack of data can often show a decline in species, but this may not be a reflection. of reality at the time, “says Bonsor.
“Our data currently do not show that they were in decline, in fact some groups such as hadrosaurs and ceratopsians were thriving and there is no evidence to suggest they would have died 66 million years ago if the extinction event had not occurred.”
The findings are supported by another recent study, which found that North American dinosaur habitats did not decline during the Late Cretaceous.
The fossil outcrops for this region are small, which means we’re probably sampling the area and underestimating its species richness.
Systemic sampling errors like this are widespread in paleontology and, to some extent, inevitable. But relying on species richness over the total number of species also comes with its limitations.
For starters, there may be no correlation between speciation rates in dinosaur evolution and extinction. It is a hypothesis that we are making in hindsight.
“We may never know the true levels of speciation and extinction of Mesozoic dinosaurs,” admit the authors of the new paper, “but greater attention to filling gaps in the fossil record will be the primary way paleontologists will continue to build a more accurate picture of the diversity of the dinosaurs of the past “.
The new paper once again underlines the many gaps and biases in our knowledge, and the authors call for ongoing research that is detailed, regionally controlled and well spaced over time to recreate the most holistic story possible.
The study was published in Royal Society Open Science.
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