- Martha Henrik
- （Martha Henriques）
September 4, 2022 at 11:02 am
image source,NASA
Asteroid hit Earth and wiped out dinosaurs
The asteroid hit the Earth to wipe out the dinosaurs and most of the species on Earth, but mammals survived the catastrophe.
It’s the worst day for life in Earth’s history, as a furry critter scurries through a hellish world of darkness, volcanic ash and deadly heat, scouring the scorched earth for sustenance and catching an insect After that, he immediately fled back to his underground shelter. The critters are surrounded by the gigantic bodies of dead or dying dinosaurs that have threatened the poor mammals for generations.
It was a hell scene in the first weeks and months after an asteroid 10 kilometers in diameter with the power of more than a billion nuclear bombs slammed into what is today the coast of Mexico. This violent impact of landslides and fissures ended the Cretaceous era of the earth and announced the beginning of the Paleocene era. At this time, the world’s forests were in flames, huge tsunamis hit the coast, high temperature gasified rocks, volcanic ash And dust washed up miles into the atmosphere.
But life still survives in this destroyed world. Among the survivors is the earliest known primate, the Purgatorius, a mammal that looks like a cross between a shrew and a squirrel. After this global mass extinction catastrophe, the Pulgartori monkey population will definitely decrease, but the species is fortunately preserved and can be passed on from generation to generation.
This is how early mammals lived after an asteroid hit the Earth and wiped out three-quarters of all species on Earth at the time. In terms of the extinction of life, in the entire history of the earth, only the Permian-Triassic extinction event 252 million years ago (The Great Dying) surpassed the asteroid hitting the earth. . The mass extinction event caused the death of 95% of marine life and 70% of terrestrial life, but the extinction process was extremely slow, and lasted for 60,000 years, unlike the disaster of an asteroid hitting the earth suddenly from the sky.
So how did these tiny and fragile creatures, including our mammalian ancestors, survive this apocalypse?
The asteroid that hit Earth ended the Cretaceous period also ended well-known dinosaurs like Tyrannosaurus and Triceratops, and the lesser-known but rather bizarre Anzu, known as the “chicken from hell.” In addition, hadrosaurs, giraffes, and dinosaurs covered in armor were also extinct. All the above dinosaurs are all dead.
In the geological age of the Late Cretaceous, under the shadow of these giants that looked down on the earth, small mammals such as the Purgatori monkey, in terms of ecological ranking, many lived as humble and humble as rodents such as mice today. low. But these seemingly fragile creatures, including our human ancestors, miraculously survived this apocalypse. How did this happen?
image source,Science Photo Library
The earliest known primate, the Purgatori monkey, was one of the survivors of the asteroid mass extinction (Credit: Science Photo Library)
That question is precisely what Steve Brusatte, author of The Rise and Reign of the Mammals, and his colleagues at the University of Edinburgh asks. topics we have been researching.
Brusatte stressed that the day the asteroid hit Earth would be an existential catastrophe for any life on Earth, including mammals, birds (i.e., bird dinosaurs) and reptiles. “This is not an ordinary asteroid,” Brusatte said. “This is the largest asteroid to hit Earth in at least the last 500 million years. Mammals are close to extinction like the dinosaurs.”
However, many species of mammals did disappear in this unprecedented natural disaster. Sarah Shelley, a postdoctoral fellow in mammal paleontology in Edinburgh, said the diversity of mammals was already astonishingly rich in the late Cretaceous. “Many mammals are small animals that live in trees or in burrows and eat insects,” she said.
However, not all mammals are insectivores. At that time, there was also a mysterious multi-tumor tooth named after the special nodular nodules on its teeth. Shelley said, “The teeth of this mammal are lumpy, with a lot of little bumps on them, and the front is a blade-like tooth that looks like a saw. They eat fruit, nuts and seeds.”
There were also carnivorous mammals at the time, and one of the largest, Didelphodon, was a marsupial, weighing about 5 kilograms, about the size of today’s domestic cats. Shelley said, “From the anatomy of the skull and the teeth, the rat-toothed dragon had a very strong bite force and was able to crush bones, so it must be a carnivore.”
Brusatte said that after the asteroid hit the earth, many species of mammals in the late Cretaceous were mostly lost, and about 90% of mammals were extinct, but this brought unprecedented changes to the surviving animals that escaped the disaster. Chance.
Brusatte said, “You can imagine that one of our tiny ancestors, the size of a mouse, a timid little creature hiding in the shadows, but you survived this moment in Earth’s history. When a catastrophe In the past, you popped up and all of a sudden the big, scary T-Rex and long-necked dinosaurs were gone, and the whole world opened up for you.”
This mass extinction created the conditions for a multitude of new and diverse species, eventually bringing blue whales, cheetahs, dormouse, platypus and, of course, us humans.
image source,Getty Images
Dinosaurs went extinct after asteroid hit Earth (Credit: Getty Images)
First of all, here is a reminder: After the impact, the world’s forests were devoured by wildfires, the sky was filled with smoke and dust, the sky was obscured, no sunlight was visible, and plants were unable to photosynthesize. As Brusatte puts it, Earth’s ecosystems collapsed “like a house of cards.” The surface temperature of the earth was hotter than an oven due to the vicious heat pulses that fluctuated like a roller coaster, but then the earth entered a cold nuclear winter, and the temperature dropped by an average of 20 degrees Celsius for more than 30 years. While many of mammals’ most dangerous predators have disappeared, the planet’s environment has become unimaginably hostile for life.
How can mammals adapt to such a harsh environment and continue their species?
keep on being animals
Before the asteroid extinction disaster, mammals had always been small in size due to the strong competition and predation of dinosaurs, but this size has become a favorable asset for “post-disaster animal refugees”.
“These mammals look and act like mice, big and small,” Brusatte said. “Usually they lived quietly in dark corners, but after the disaster, in this new world, mammals proliferated because Its size is perfect for the terrifying environment of an asteroid hitting Earth.”
Small size may help speed up animal reproduction to increase numbers. In the modern animal world, “the bigger you are, the longer the pregnancy,” said Ornella Bertrand, a postdoctoral fellow in mammalian paleontology at the University of Edinburgh. For example, the gestation period of African elephants is 22 months, while the gestation period of mice is only about 20 days. Therefore, in the event of an apocalypse, the smaller mice have a greater chance of maintaining population growth.
In addition to longer gestation periods, larger animals also took significantly longer to reach sexual maturity, especially giant dinosaurs. That’s another reason why dinosaurs couldn’t survive apocalypse. “Dinosaurs took quite a while to mature,” Brusatte said. “An animal like Tyrannosaurus rex took about 20 years. That’s not to say dinosaurs didn’t grow fast, it’s just that many dinosaurs were too big. Huge, it takes a long time to grow from a very small pup to an adult behemoth.”
Hide underground and escape
Another clue to solving the mystery of mammals surviving after the asteroid hit Earth is that mammal fossils found in Paleocene and earlier strata have “very strange” body shapes. Mammalian ankle bones found in early Paleocene strata are small, tough, dense and well-preserved. Shelley analyzed the ankle bones to see how similar these mammals were to those that live on Earth today.
“We found that Paleocene mammals were strange and different from modern mammals,” she said. “What they had in common was that they were small but strong.”
image source,PA Medium
Small size may help speed up animal reproduction
Shelley said these mammals, with their strong muscles and huge bones, were most similar to those of today’s animals that burrowed in the ground. “The resulting hypothesis is that animals that survived the mass extinction had a survival advantage in that they burrowed and roosted and thus survived the first wave of catastrophe following a direct impact, and subsequent ground fires and In nuclear winter, they just need to lurk a little underground and wait for the disaster to pass.”
Let me put it this way, because the survivors of these extinctions survived, so their descendants also inherited this sturdy size. Shelley said, “You can see this mammal for 10 million years in the Paleocene period, and it was still very bulky even in trees.”
If the surviving mammals do live underground, either by burrowing themselves or in the underground burrows of other animals, Bertrand conjectures that this may also be reflected in the agility of these mammals, or in other words Lack of agility. “We know that the forest has been destroyed, so all the tree-dwelling animals have lost their habitat,” she said. “So one hypothesis is that the surviving animals are rarely as nimble as the arboreal animals.”
Bertrand intends to study the inner ear skeletons of mammals from this era to see if his findings support the hypothesis that the mammals survived by hiding in the ground after the asteroid impact. The inner ear plays a major role in the balance of the animal’s limbs, and if the animal needs to have dexterous and agile movements, their skeleton will have a corresponding fine structure. But if the animal needs only the physical strength to dig holes, the agility is superfluous. “It could give us more clues,” she said. That said, Bertrand also noted that over-reliance on skeletons to infer animal motor behavior is also flawed, as she watched the recent Commonwealth Games. Impressed.
Bertrand said with a laugh, “I see gymnasts doing crazy things and I thought, it’s funny, we have the same bone structure, and I just can’t do it. I think, it’s really funny because maybe having This ability helps you survive, but you don’t know from the bones whether you have it or not.”
Omnivore gives survival advantage
Asteroids destroyed most of the living plants on Earth, and plants are the lowest link in the many food chains on Earth’s land. Omnivorous mammals can eat any food, and are better adapted to the environment than animals that only eat certain special foods, so they have a better chance of survival.
Shelley said, “The animals that survived this mass extinction basically didn’t have a very specific diet.” For example, Didelphodon, a close relative of a cat-sized carnivorous marsupial, preyed only on certain species, but the animals it preyed on became very rare after the mass extinction. Shelley said, “Sraurodon’s food was too monotonous, so it lost its way of survival. But if it was a small animal, it could change its diet and lifestyle more quickly to adapt to the environment. It survived the mass extinction. good idea.”
In addition to the survival of animals that can eat everything, Brussat said, there are very few animals with special diets who will have an advantage, especially those who eat plant seeds are lucky. “Seeds are a food bank that doesn’t run out,” he said. “Any animal that was already feeding on seeds could get them in the event of a mass extinction. So if an animal like a Tyrannosaurus rex was out of luck, evolution didn’t give The ability of these animals to digest seeds. But for birds with beaks and some mammals that specialize in eating plant seeds, wow, is this just about time?”
In addition to keeping stricken animals alive, plant seeds also help rebuild forests and vegetation after the nuclear winter has disappeared. “The seeds survived the mass extinction in the soil, and when the sun came down again, those seeds started to sprout and grow,” Brusatte said.
Long body but not brain
As the Paleocene passed, ecosystems recovered, and the earth was full of life again, mammals began to fill the void left by non-avian dinosaurs and became the strongest species of life on earth. “Immediately after the extinction of the dinosaurs, mammals began to diversify, and in every respect,” Bertrand said.
First, mammals’ bodies grew rapidly. But the Edinburgh team found that changes in brain size in mammals have not kept pace with body size.
“I think it’s very important because we thought it might be the development of intelligence that allowed mammals to survive and eventually rule the planet,” Bertrand said. “But, from the data, it’s not the growth of brains that allowed animals to live on asteroids.” survive the impact.”
image source,Science Photo Library
Mammals need the entire body to become larger and stronger to adapt to the environment
In fact, in the early Paleocene, mammalian brains, if too large relative to their bodies, may not have been conducive to survival. Bertrand asked, “The question is why do you need a big brain? Actually, getting a big brain is pretty expensive. If you have a big brain, you need to eat a lot to maintain it, and if you don’t have enough If you don’t have food, you will become extinct.”
Instead, mammals need their entire bodies to become larger and stronger in order to adapt to their environment. In the hundreds of thousands of years after its extinction, the herbivore Ectoconus reached a weight of about 100 kilograms. Ectoplasts belong to the family Periptychidae, which may be related to extant hoofed mammals. Hundreds of thousands of years are in the blink of an eye. Shelley said, “It’s amazing how exocones can grow so big so quickly, and become herbivorous so quickly. You see, once there are large herbivores, there are also large carnivores, mammals. It started to evolve rapidly.”
There are also many other mysterious mammals with rapidly expanding bodies. Shelley said, “animals like the toothed beast grow very fast and grow very large.” The complete skeleton of the toothed beast has not yet been found, but a fossil skull has been found. Its skull is about a large The size of the butternut squash, the toothed tooth appears to be one of those species that only grew strong enough to burrow in the aftermath of the mass extinction. Shelley said, “It has a small eye position, small eyes, but huge teeth in front of it. It’s a bit like a rodent, but that’s all. It’s a very mysterious animal.”
Shelley said that these mammal species, which evolved rapidly from post-mortem fauna, had long been ignored by the scientific community. The scientific community, she said, “thought they were ancient, primitive, and unremarkable, but that’s not the case, they are really unique. Their ancestors survived the second mass extinction in the history of life on Earth, and it was by no means slow. Ordinary stupid animals that gobble their lives. They survive and reproduce wonderfully.”
In many ways, these mammals filled the ecological space left by the tragic extinction of the dinosaurs. The living habits are highly individualized, and the giant dinosaurs were well adapted to the ecological environment of the late Cretaceous period, but lacked the ability to survive in the cataclysmic world after the asteroid impact.
Brusatte said, “The most shocking thing is that we once had animals like dinosaurs on our earth, they lived for 100 million to tens of millions of years, and created such a great and glorious history, such as evolving themselves into airplane-sized animals. Behemoths, and carnivores as big as buses, etc., but when the earth suddenly suffered a huge change, these behemoths were completely wiped out in an instant. Dinosaurs could not cope with the new world and could not adapt to survive.”
image source,NASA
The dinosaur-killing asteroid burst through the atmosphere and hit Earth faster than a bullet (Credit: Nasa/JPL-Caltech)
The randomness of the asteroid impact event seems to be particularly impressive to a team of researchers at the University of Edinburgh, who study how mammals took refuge in the aftermath of the mass extinction.
Bertrand said, “We humans came to this world today mainly by luck. The asteroid that hit the earth could pass by the earth, or it could fall into the ocean in another part of the earth, no matter where it is. This possibility will make the selection and evolution of life species in the future have different results. Whenever I think about the contingency of this whole thing, I think it is incredible.”
Brusatte felt the same way. He said, “The asteroid may just whizz past the Earth, it may only stir the upper layers of the atmosphere, or it may have disintegrated as it approached the Earth. There were all kinds of possibilities for this asteroid, but it was really bad luck. It hit the earth straight.”
But for mammals living on Earth today, this catastrophe may be a godsend.