The fall of an asteroid on the Yucatan Peninsula 66 million years ago is only part of the history associated with the extinction of then 75% of known life forms, indicates a famous popularizer of science in America. The distinction between survivors and those who died as a result of that disaster resembles a pattern that has been validated for millions of years, both before and after the fall of the asteroid.
The reason why our planet has lost these terrible and ancient lizards may seem obvious. About 66 million years ago, an asteroid fell from heaven to earth with a wild roar, and the place of its fall was the current Yucatan Peninsula in Mexico. The devastating consequences were unprecedented - a tsunami, an overheated atmosphere, a darkened sky, a terrible sudden cold snap, as well as other apocalyptic environmental events, as a result of which an estimated 75% of known life forms on our planet were destroyed.
Paleontologists call this disaster the Cretaceous-Paleogene extinction (K / Pg extinction), as it signifies the transition from the Cretaceous to the Paleogene in the history of the Earth. Although the event is under constant study, its details are still a mystery to scientists. This case was not closed after the discovery in the 1990s of the crater formed after the fall of the asteroid, as well as the establishment of exactly how the destruction of existing life forms took place (and what distinguished the surviving forms from the dead). All this continues to inspire paleontologists and makes them deeply study this cataclysm of the Cretaceous period.
To better understand this whole story as a whole, researchers are moving away from the moment the asteroid fell and studying an expanded number of life samples of that time. Dinosaurs did not live in a stable and abundant Mesozoic utopia, and they were not the only living organisms at the time - far from it. The world around them then changed, as it always happened. As the Cretaceous period drew to a close, sea levels dropped, the climate grew colder, and a part of prehistoric India called the Trapps of the Deccan Plateau was a highly volcanic site. It is not easy to understand how these changes affected life on Earth, especially after a catastrophic meteorite impact changed the structure of rocks. Nevertheless,paleontologists scrutinize the sediment samples at the time to understand what happened.
“To understand what happened after this asteroid hit Earth, we need accurate baseline data on the background extinction before the Cretaceous-Paleogene catastrophe,” said Paul Barrett, paleontologist at the Natural History Museum. The moment of catastrophe makes sense only in the framework of a broader context, testifying to the existing life forms before and after it. "And then it will be possible to talk about whether the Chicxulub event was the main cause of the extinction, or it was just the final blow that ended the ecosystem, the stability of which was gradually decreasing."
Although the Cretaceous-Paleogene extinction was a global crisis, its processes in various places on our planet remain unexplored. The amount of information on any particular site depends on how well the fossil layers are preserved and how accessible they are to researchers. Some locations with the best accessibility are in western North America, where there is a continuous sequence of sedimentary strata data from the late Cretaceous and early Paleogene. These rocks contain both pre-extinction and post-extinction material, and it was this data that became available that allowed Royal Saskatchewan Museum paleontologist Emily Bamforth to study what happened over the 300,000 years before the explosive completion. Cretaceous period.
Looking at the geologic deposits in southwestern Saskatchewan, Bamforth said local conditions, including the number of wildfires and the characteristics of specific habitats, were as important as what happened globally in identifying samples of ancient biodiversity. … “In my opinion, this is an important message to bear in mind when analyzing the causes of the disappearance,” says Bamforth. “Each individual ecosystem may have its own smaller biodiversity incentives that were in place prior to extinction, and these can be considered part of larger, global drivers.” What was good for turtles, amphibians, plants, dinosaurs and other organisms in one place may not be so good in another place.and therefore we cannot properly understand global shifts without considering the foundations of local diversity. “Ecosystems are complex and I think it makes sense to keep that in mind when discussing the causes and duration of mass extinction,” notes Bamforth.
For Saskatchewan, the pre-extinction ecological community was like a Jenga game. “The top remains intact, but factors such as climate change are gradually chipping away at it, weakening the system and making it vulnerable,” says Bamforth. The ever-shifting ecological stability makes major problems especially catastrophic - like an asteroid that falls in the wrong place at the wrong time.
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The picture of the shifting ecosystem redirects the focus of the Cretaceous-Paleogene catastrophe. While the reasons for the extinction of non-avian dinosaurs and other organisms are grabbing our attention, scientists have a harder time answering the question of why surviving species were able to make it through the next chapter of life history.
Those species that were able to survive the consequences of the disaster that occurred were, as a rule, small in size, half aquatic and, in addition, were able to consume a variety of foods, however, there are some key contradictions in this respect. There were also small non-avian dinosaurs that had similar advantages, but nevertheless became extinct, as did numerous reptiles, birds and mammals, despite their belonging to broader extant groups. So, for example, the didelfodons, a mammal the size of a badger, could not survive, just as the ancient Avizaurus birds could not do this.
“There is one thing I’m trying to explain,” Barrett says. In general, small dinosaurs and other animals should have had a better chance of survival than their larger relatives, but this was not always the case.
Pat Holroyd of the University of California Museum of Paleontology compares such research to what happens after an airplane crash. “Rescuers go there and collect all the data, and then experts try to understand what happened. "Why did the people in the tail section survive, and those passengers who were in other places died?" Holroyd asks. While these events may be special and their causes are unique, it is nevertheless possible to look at numerous incidents of this nature, define patterns, and provide information on what we think about a particular event.
As for the Cretaceous-Paleogene extinction, such patterns are still emerging. According to Holroyd, a significant amount of data, drawn from meaningful research on the species that survived the disaster, has only been published or sent to the Paleobiology Database in the past decade. This new information allows Holroyd and her colleagues to study patterns of change - how long certain species were able to survive on land and in nearby freshwater bodies - long before the asteroid hit, as well as after the disaster itself. The team's findings were presented earlier this fall at the Society of Vertebrate Paleontology annual conference in Albuquerque, New Mexico.
Some of the models were already known. Fish, turtles, amphibians and representatives of the order of crocodiles - all of them, as a rule, have more abilities than strictly terrestrial organisms. “Experts have been observing these patterns since at least the 1950s, and possibly even earlier,” Holroyd notes. However, the resilience of amphibian species has never been determined in detail, and new research suggests that the solution to the riddle of the extinction model was right in front of us from the very beginning.
To Holroyd's surprise, the distinction between survivors and those killed by the Cretaceous-Paleogene catastrophe actually resembles the pattern that has been validated for millions of years both before and after the asteroid's impact. Terrestrial species of living things, especially large ones, do not have the same ability to survive as those that live in freshwater environments. Terrestrial species often go extinct at a faster rate than those found in aquatic environments, even without the impact of a major disaster. The species that lived in and around freshwater bodies appeared to last longer, and when extinction at the end of the Cretaceous period peaked, these organisms had an advantage over their purely terrestrial neighbors.
But even in this kind of relatively safe aquatic environment, things were not so rosy for the animals that lived in the water. According to Holroyd, Cretaceous turtles, for example, have lost 50% of their diversity globally, although losses were only 20% in more localized areas in western North America, further highlighting the importance of understanding local versus global patterns. Even those groups that can be considered “survivable” may suffer losses and not return to their previous glorious development. For example, marsupial mammals were able to survive the consequences of the disaster as a group, but their diversity was significantly affected, and the number was significantly reduced.
The question of how local ecosystems have been affected by these changes is the next step towards understanding how species extinction has affected the world. Holroyd cites Triceratops as an example. They were widespread throughout much of western North America during the late Cretaceous and were certainly an important part of the ecosystem. Bison were such animals at one time, and given how these herbivores change their habitat through grazing and migration, the extinction of Triceratops, that is, three-horned dinosaurs, undoubtedly led to significant consequences for the ecosystem that was in the process of restoration after the Cretaceous disaster. Plants that were likely dependent on Triceratops to spread their seeds were affected, while other plants,which were previously trampled by dinosaurs, now have the opportunity to develop more freely. How the constituent parts of an ecological system are formed, and what they mean for recovery from a disaster - these questions should now be fully in the focus of our attention.
“The western interior of North America is the only window for us to get an idea of what happened to living organisms on earth as a result of the Cretaceous-Paleogene catastrophe, but it is completely unclear if this is typical,” said Barrett. “We have no idea how intense the extinction process was in various parts of the world,” especially in those places that were at a considerable distance from the asteroid's fall. “It seems unlikely that there is a one-size-fits-all model” that would determine the fate of such distinct organisms as edmontosaurs on land and shell ammonites in the sea, as well as numerous other species that perished in the Cretaceous disaster. Research in Europe,South America is just beginning to form the basis of a much needed global picture of the most famous extinction process in history.
“It’s like a giant jigsaw puzzle that we started putting in more and more pieces,” notes Bamforth. Over time, a complete picture of this critical moment in Earth's history will be recreated.
Brian Switek