The dinosaurs were in their prime, not in decline, when the fateful asteroid struck

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Paleontologists agree that a massive asteroid strike triggered the end of the dinosaurs, but a debate has persisted about the reptiles’ general condition at the time of the fateful collision.

Were non-avian dinosaurs already in decline, and the asteroid just speeded them toward extinction?

Or did they thrive in the late Cretaceous, only to be wiped out by an ill-timed space rock?

A recent study led by the University of Edinburgh provides new evidence that the dinosaurs were going strong at the time of their sudden demise. By combing through the fossil record to reconstruct food webs in the millennia before and after the asteroid’s strike, the researchers also shed new light on how some mammals and birds survived a catastrophe that ended 165 million years of dinosaur life.

“This is a very interesting study that uses an approach not often used in vertebrate paleontology,” said paleontologist Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County, who was not involved in the research. “The results are solid.”

The study, published this month in the journal The progress of sciencereviewed more than 1,600 fossil specimens from the 18 million years before the asteroid struck—the last years of the Cretaceous period—to the first 4 million years of the Paleogene period, which began the day the 7.5-mile-wide rock smashed into what is now Mexico’s Yucatan Peninsula.

The fossils represented virtually every type of animal that ate and was eaten during that time, from fish, salamanders and frogs to crocodiles, dinosaurs and mammals.

By looking at the number of remains found, the researchers concluded that the dinosaurs had a stable, robust place in the ecological web at the time of their death, with no indication in the fossil record that their food sources were in decline, said lead author Jorge García-Girón, an ecologist at both Finland’s University of Oulu and Spain’s University of León.

With far less security in the food web than their dinosaur counterparts, mammals spent the late Cretaceous trying to gain a small, furry foothold in a landscape dominated by giant reptiles. Scientists found a wide diversity of mammal species, suggesting a family adapting to their world.

“It’s kind of a trade-off,” García-Girón said. “The dinosaurs were far more stable in their ecologies. They were, of course, masters of their ecosystem. Mammals, on the other hand, diversified and began to colonize different habitats and different environments.”

When the asteroid hit, this flexibility may have been the mammals’ saving grace.

The Cretaceous-Paleogene extinction, or K/Pg event, wiped out an estimated 75% of species on the planet at the time. When the impact came, and the ensuing fires and clouds of particulate matter seared the landscape and transformed the atmosphere, most dinosaurs couldn’t burrow underground, fly to safer territory, or immerse themselves in water to ride out the worst of it, as surviving species did.

“The asteroid impact was so great that there was no place on Earth’s surface that was truly safe,” author Riley Black wrote in the book “The Last Days of the Dinosaurs: An Asteroid, Extinction, and the Beginning of Our World.” “When the air itself became mortal, there was little that could be done for earthly life.”

Dinosaurs were ideally suited to the landscape and climate of the late Cretaceous. When a singular, unexpected event eliminated that world overnight, the dinosaurs followed.

While the new research answers questions about a significant event in the planet’s past, it could also help scientists interpret the future. Understanding the five mass extinction events in prehistoric history can help us predict how plant and animal species may suffer and decline as a result of anthropogenic climate change.

Freshwater species, for example, are already disappearing rapidly, García-Girón said. “If we are able to discern what kinds of factors determined the survival of freshwater fauna in the past, we may be able to use that information to predict the consequences of freshwater biodiversity loss occurring in our time,” he said.

More information:
Jorge García-Girón, Changes in food webs and niche stability shaped survival and extinction at the end of the Cretaceous, The progress of science (2022). DOI: 10.1126/sciadv.add5040. www.science.org/doi/10.1126/sciadv.add5040

2022 Los Angeles Times.
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Citation: Dinosaurs were in their prime, not in decline, when fateful asteroid impact (2022, December 25) Retrieved December 25, 2022, from https://phys.org/news/2022-12-dinosaurs-prime-decline-fateful – asteroid. html

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