Sixty-six million years ago, an asteroid the size of San Francisco crashed into a shallow sea off the coast of present-day Mexico, plunging the world into an extinction event that wiped out 75% of life, including the dinosaurs. However, debate continues as to how the Cretaceous-Paleogene (K-Pg) extinction event affected plant life on land; This is partly because global fossil surveys show that none of the major plant families became extinct.

A new analysis of fossil data from North and South America sheds light on how plants lived during the K-Pg boundary and points to a true plant extinction, a team of scientists reports in the new journal Cambridge Prisms. extinction.

“There is a tendency in the literature to say that this event may have been bad for dinosaurs and a lot of marine life, but it was good for plants because of the survival of large groups,” said Peter Wilf, lead author and professor of earth sciences at Penn State. “Our review contradicts this idea, because everywhere we looked more than half of the species became extinct.”

Fossil plant collections are necessary to understand what happened to ancient plants during the extinction, the scientists said, and for K-Pg they were previously limited to just a few areas in the United States. New fossils from Colombia, Argentina and the United States provided a wider geographical range to examine the severity of the event, its ecosystem consequences and its legacy on plant life.

“You need a really big study to know where the rocks are where plant fossils are found,” Wilf said. “DNA differences between living plants tell you nothing about deep species extinctions. You need before and after plant fossils. You need rock layers that show extinction. And the more indicators you have, the more complete your story.”

The researchers looked at new fossil data from North Dakota, Colorado and New Mexico in the United States, as well as Colombia and Argentina. Scientists say the evidence points to a significant loss of plant species, of more than 50% in every region.

According to scientists, this loss of species means literal extinction. For example, modern conservation efforts focus on protecting species like the polar bear rather than the larger group to which it belongs (all bears or all mammals). Applying this to plants, the extinction of an entire modern plant family such as the Fagaceae would also require the extinction of all species of beech, chestnut, and oak.

“You can’t actually kill most plant families, so this claim is a bit ridiculous,” Wilf said. “By the end of the Cretaceous period, each family had so many genera, containing so many species and individuals. Plants were two hundred times more numerous than all animals combined. Dinosaurs were much less diverse and numerous than plants, and were therefore much easier to kill in almost all their major categories; only the birds survived.”

“We remind our colleagues that these extinctions of plant species are real, very serious extinctions. Everywhere we look, wherever records survive, we see a massive loss of plant species, followed by a series of astonishing evolutionary events that shaped our modern world into what it is today.”

The extinction of K-Pg ushered in the rise and true dominance of flowering plants and helped form the planet’s rainforests, which contain much of the biodiversity, Wilf said.

“Mass extinctions are not just taxonomic losses,” said Monica R. Carvalho, an associate professor at the University of Michigan and co-author of the study. “There is a transformative impact on ecosystems; what they are made of, how they work. “Fossils show that after the extinction of tropical forests, they were radically different from their predecessors in composition, structure and ecology.”

According to scientists, the extinction in all regions studied had a transformative effect on plant life and terrestrial ecosystems.

“The goal was to let everyone know that we have these different areas and compare them,” Wilf said. “This allows us to address this question of heterogeneity – whether everything is a monolith – whether the extinction of plants at the end of the Cretaceous period was the same everywhere. This paper shows that this was not actually the case, that very different things were happening in different places.”

Factors such as distance from the impact site, Chicxulub Crater off the coast of the Yucatan Peninsula in Mexico, and how sensitive local plant life would be after the impact to freezing conditions caused by global darkness likely influenced these differences.

“These extinctions were partly a result of the planet freezing and may have been particularly severe in the tropics,” Wilf said. “This is a region that doesn’t like freezing very much, and it’s also very diverse. It was a warm world without a lot of frost. After the first tsunamis, shock waves and similar events, the best place to go was closer to the coast to buffer the sea temperature.”

According to scientists, the K-Pg extinction is considered similar to the current biodiversity crisis; because both involve large-scale environmental changes over a geologically instantaneous period of time. Global conservation assessments show that a comparable number of plant species (about 40 percent) are now at risk of extinction, and their loss could lead to ecological consequences comparable to K-Pg extinction, Wilf said.

“Although the worst outcomes are still avoidable, the sixth mass extinction could mirror the K-Pg event, wiping out a comparable number of plant species in a geological instant, causing great damage to biodiversity, ecosystems and civilizations,” Wilf said. said. “This could then alter terrestrial ecosystems and have small impacts on global plant family diversity.” Source