Dinosaurs and fossil lovers are familiar with the meteorite attack that drove Tyrannosaurus rex and all non-natural dinosaurs to extinction about 66 million years ago. But it is often overlooked that the impact also wiped out entire ecosystems. A new study has shown how those victims in turn led to a particularly profound evolutionary outcome: the rise of South America’s Amazon rainforest, the most spectacular environment on the planet. Yet the Amazon’s abundance of tropical species and habitats faces their own existential threat due to unprecedented destruction by human activities, including land clearance for agriculture.
The new study, published in Science on Thursday, analyzed tens of thousands of plant fossils and “a fundamental advance in knowledge,” said Peter Wilf, a geoscientist at Pennsylvania State University who was not involved in the research. “The authors show that the extinction of dinosaurs was also a giant event for neotropic ecosystems, which brought their evolution to a whole new path that leads directly to the extraordinary, diverse, spectacular and severely endangered rainforests in the region. “
These insights, Wilf adds, “provide new impetus for the conservation of the living evolutionary heritage in the tropics that support human life, along with millions of living species.”
Carlos Jaramillo, a paleobiologist at the Smithsonian Tropical Research Institute in Panama and co-author of the study, agrees that the meteorite’s evolutionary and ecological effects have implications for the rapid, human destruction of the Amazon rainforest and other important habitats. across the planet. “We can connect it now,” he says, “because we are also transforming landscapes and it lasts forever – or at least for a very long time.”
Analysis of about 50,000 pollen grains and 6,000 fossil leaves shows that the meteorite that wiped out non-natural dinosaurs also created the Amazon rainforest.
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Contemporary rainforests are an integral part of life on earth. The Amazon plays a particularly important role in regulating the planet’s freshwater cycle and climate. Yet Western European and North American paleontologists paid little attention to tropical forests, but instead focused on moderate latitudes. Many academic and amateur fossil hunters also tended to write off hot, wet areas as a lost cause for finds because they assumed conditions there would prevent organic materials from being stored long enough to fossilize. ‘It is this combination of factors that has led us to the absence of much data in the tropics,’ says Bonnie Jacobs, a paleobiologist at Southern Methodist University, who co-authored a contextualizing essay working with the new study in Science has been published.
Scientists already knew that the effects of the meteorite collision and its effects – at least in temperate zones – vary with local conditions and distance from the Chicxulub impact crater in the Yucatán Peninsula in Mexico. New Zealand forests, for example, have escaped relatively unscathed. But researchers had no idea how the tropical rainforests of Africa or until now those of South America had changed.
Along with most of his co-authors, Jaramillo is from Colombia and he specifically wanted to explore the origins of his tropical forests from his homeland. The new study, which he conceptualized as an undergraduate student, represents nearly 12 years of effort. “It took us a long time,” he says, “because we had to start from scratch.”
Whole trees are virtually never preserved in the fossil record, and Jaramillo and his colleagues turned to petrified pollen and leaves for insight. Pollen preserves well over time and is widespread in the fossil record. Like leaves, it differs morphologically between species, which helps researchers determine what species of plants lived in an ancient habitat.
Jaramillo and his colleagues searched 53 sites across Colombia for rocks that formed during the Late Cretaceous, just before the meteorite attack, and others that formed during the next ten years in the Paleogene period. From these rocks, the team collected and analyzed about 50,000 fossil pollen grains and 6,000 fossil leaves to characterize the species of plants that made them. Recent separate findings indicate that plant leaves that receive more light have a higher density of veins, as well as a higher ratio of a natural isotope called carbon 13. The researchers studied the characteristics of the collected fossils to determine the structure of the region’s to merge past. woude.
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Their findings paint a picture of a sudden, catastrophic destruction of life after the impact – but also of a phoenix-like rebirth in the millions of years that followed. Before the meteorite, the authors determined, the forests in South America had many conifers and a brightly lit canopy with lush bottom ferns. Dinosaurs probably played a key role in the maintenance of these Chalk Forests by, among other things, cutting down trees and eradicating vegetation. Within moments of the impact of the Chicxulub meteorite, however, this ecosystem was irrevocably changed. Fires, which probably burned for several years, engulfed South America’s southern forests. Along with many of the animals they support, a total of 45 percent of the continent’s tropical plant species have disappeared, according to the authors’ calculations.
It took six million years before the forests returned to the level of diversity they had before the meteorite, and the species that were slowly growing back were completely different from what had come before. Legumes – plants that form symbiotic relationships with bacteria that enable them to dissolve nitrogen from the air – first appeared, and this enriched the soil that was previously nutrient-poor. This supply of nitrogen, together with phosphorus from the ash of the meteorite, enabled other flowering plants to thrive along the legumes and displace conifers. As flower species competed for light, they formed dense foliage of leaves and created the low Amazon rainforest we know today, characterized by a blanket of productivity at the top and a dark undergrowth at the bottom.
Regan Dunn, a paleo-ecologist at the La Brea Tar Pits and Museum in Los Angeles who was not involved in the new study, agrees that its findings are not only the key to revealing the past, but also to put the current anthropogenic threats into perspective. She notes in particular the authors ‘calculation that 45 percent of the plant species became extinct as a result of the meteorite collision, because’ current estimates indicate that at least as many plant species worldwide will be threatened in the Amazon basin in the next 30 years. ”
“The question remains: how will the human impact change the composition and function of Amazon forests forever?” Say Dunn.
The new findings show how extensive mass extinction events can ‘change the course of everything’, says Jacobs. Today we are in the midst of another such event, she adds, but this is driven by a single species – and there is no place far from the metaphorical impact crater “because humans are ubiquitous.”
But unlike past events from mass extinction, Jacobs says, “we are not powerless to stop it.”