How the "Great Worlds" mammals survived the apocalyptic world after the extinction of the dinosaurs

The impact of an asteroid on Earth led to the extinction of the dinosaurs

The impact of the asteroid on Earth exterminated the dinosaurs and destroyed most species on Earth, but mammals survived the apocalypse.

It was one of the most painful days of life in earth's history, when a furry little animal scurried in terror through the darkness, volcanic ash, and deadly heat of hell, searching for food on the charred earth, catching an insect, and immediately fleeing back to its underground shelter. The small animals are surrounded by the huge bodies of dead or dying dinosaurs, behemoths that have threatened the survival of poor mammals for generations.

It was a hellish scene in the first weeks or months after an asteroid with a diameter of 10 kilometers and more than 1 billion nuclear bombs hit the coast of today's Mexico. The violent impact of this landslide crack ended The Cretaceous era and heralded the beginning of the Paleocene era, a time when the world's forests were on fire, huge tsunamis hit the coast, and hot gasified rocks, ash and dust washed up miles into the atmosphere.

But there is still life alive in this destroyed world. Among the survivors are the earliest known primate, the Purgatorius, a mammal that looks like a hybrid of shrews and squirrels. After this global mass extinction disaster, the number of Purgatori monkeys will certainly decrease, but fortunately the species has been preserved and can be passed on from generation to generation.

This is what happened to early mammals after the asteroid struck The Earth and exterminated three-quarters of the species on Earth at the time. In terms of the intensity of life extinction, in the entire history of the earth, only the Permian-Triassic extinction event 252 million years ago, that is, The Great Dying event, surpassed this asteroid collision with the earth. Mass death extinction events caused 95 percent of marine life and 70 percent of terrestrial life to die, but the extinction process was extremely slow and long, up to 60,000 years, unlike the asteroid hitting Earth disaster that suddenly came from the sky.

So how did these tiny and fragile creatures, including our mammalian ancestors, survive this end of the world? Hitting Earth ended the Cretaceous asteroids and also ended famous dinosaurs such as Tyrannosaurus and Triceratops, as well as the lesser-known but rather bizarre Anzu, known as the "Chicken from Hell." In addition, there are platypus, long-necked dinosaurs, and dinosaurs with armor all over their bodies. All of the above dinosaurs were dead.

In the geological age of the Late Cretaceous, in the shadow of these earth-auror giants, small mammals such as the Pulgatori monkey, many of them lived as humble and inferior in ecological ranking as rodents such as rats today. But how did these seemingly fragile creatures, including our ancestors, miraculously survive the end of the world?

The Purgatori monkey, the earliest known primate known to man, was one of the survivors of the mass extinction of an asteroid impact on Earth (Credit: Science Photo Library)

This question is exactly what Steve Brusatte, author of The Rise and Reign of the Mammals, and his colleagues at the University of Edinburgh have been working on.

Brussart stressed that the day the asteroid hits Earth is an existential catastrophe for any life on Earth, including mammals, birds (i.e., avian dinosaurs) and reptiles. "This is not an ordinary asteroid, it's the largest asteroid that has hit Earth in at least the last half a billion years," Brusart said. Mammals were almost extinct like dinosaurs. ”

However, many species of mammals did disappear in this unprecedented natural disaster. Sarah Shelley, a postdoctoral fellow in mammal paleontology in Edinburgh, said mammalian diversity was already surprisingly rich during the late Cretaceous period. "A lot of mammals are small animals that live in trees or burrows and eat insects," she said. ”

However, not all mammals are carnivores. At that time, there was also a mysterious polynoodontic beast, named because of the special nodules on the teeth. Shelley said, "The mammalian teeth are lumpy, with a lot of small pimples on them, and the front is a blade-like tooth that looks like a saw." They eat fruits, nuts and seeds. ”

There were also carnivorous mammals at the time, and one of the largest, the Didelphodon, was a marsupial that weighed about 5 kilograms and was about the size of today's domestic cats. Shelley said, "Judging from the anatomy of the skull and teeth, the bite force of the rat mole is very strong, and it can bite the bones, so it must be a carnivore." ”

Brusart said that after the asteroid hit Earth, many species of mammals in the late Cretaceous period mostly disappeared, and about 90 percent of mammals were extinct, but this gave an unprecedented opportunity for survivors who escaped the disaster.

Brusart said, "You can imagine that one of our tiny ancestors, the size of a mouse, a little thing hiding in the shadows, cowardly, but you survived this moment in the history of the earth." When the disaster passes, you emerge and suddenly find that the terrible big guys of the Tyrannosaurus Rex and the giraffe dinosaur have disappeared and the whole world is open for you. ”

This mass extinction set the stage for a large variety of new species, eventually bringing blue whales, cheetahs, sleeping mice, platypus and, of course, us humans.

After the asteroid hit the Earth, the dinosaurs went extinct

First of all, here is a reminder: after the impact, the world's forests were engulfed by wildfires, the sky was filled with smoke, the sky was covered, the sun was invisible, and plants could not photosynthesis. As Brussart puts it, earth's ecosystems collapsed "like houses of cards." The Earth's surface temperatures became hotter than ovens by a vicious heat pulse that fluctuated like a roller coaster, but then the Earth entered a cold nuclear winter, with temperatures dropping by an average of 20 degrees Celsius for more than 30 years. While many of mammals' most dangerous predators have disappeared, earth's environment has become unimaginably harsh for life.

How can mammals adapt to such harsh environments and continue their species?

Keep making small animals

Before the asteroid extinction catastrophe, mammals had been small due to strong competition and predatory restrictions from dinosaurs, but this size became a favorable asset for "post-disaster animal refugees" for the rest of their lives.

Brussart said, "These mammals look and behave like rats large and small. Usually surviving quietly in the dark corners, but after the disaster, in this new world, mammals thrive because their size is perfect for the terrible environment after the asteroid hits the Earth. ”

Small size may help accelerate animal reproduction and increase numbers. Ornella Bertrand, a postdoctoral fellow in mammal paleontology at the University of Edinburgh, said that in the modern animal world, "the bigger you are, the longer you are pregnant". For example, African elephants have a gestation period of 22 months, while mice have a gestation period of only about 20 days. So in the event of an apocalyptic catastrophe, small rats are more likely to keep their populations growing.

In addition to the long gestation period, larger animals also take much longer to reach sexual maturity, especially the behemoth dinosaurs. This is another reason why dinosaurs could not survive apocalyptic apocalypse. Brusart said, "It took quite a long time for dinosaurs to grow and mature. Animals like rex tyrannosaurs take about 20 years. This is not to say that dinosaurs did not grow fast, but many kinds of dinosaurs were too large, and it took a long time to grow from very small cubs to adult behemoths. ”

Hide underground and escape

Another clue to the mystery of the survival of mammals after an asteroid hit Earth is that mammal fossils found in Paleocene and earlier strata have "very strange" body sizes. Mammals found in the Early Paleocene formation have small, tough ankle bones, high density and well-preserved. Shelley analyzed these ankle bones to see how similar these mammals were to the mammals that live on Earth today.

"We found Paleocene mammals strange, unlike modern mammals," she said. What they have in common is that they are short but strong. ”

Small size may help accelerate animal reproduction and increase numbers

Shelley said the mammals had strong muscles and massive skeletons, most similar to the species of animals today that live by digging burrows in the ground. "The resulting hypothesis is that the animals that survived the mass extinction have a survival advantage in that they dig holes and therefore survive the first wave of catastrophe after a direct impact, as well as the subsequent ground fires and nuclear winters, and they only need to lurk slightly 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 strong body shape. Shelley said, "You can see this mammal for 10 million years in the Paleocene period, and even living in trees is still bulky." ”

If surviving mammals did live underground, either by digging their own burrows or living in the underground burrows of other animals, Bertrand conjectures that this may also be reflected in the mammals' agility, or in other words lack of agility. "We know that the forest has been destroyed, so all the animals that live in the trees have lost their habitat," she said. Thus, one hypothesis is that surviving animals are rarely as agile as arboreal animals. ”

Bertrand intended to study the inner ear skeletons of mammals of this era to determine whether its findings confirmed the hypothesis that these mammals survived by hiding underground after an asteroid impact. The inner ear plays a large role in the balance of the animal's limbs, and if the animal needs to have dexterous and agile movements, their bones will have corresponding fine structures. But if the animal only needs to have a strong body to dig a hole, the agility ability is superfluous. "This can give us more clues," she said. That being said, Bertrand also points out that there is also a flaw in relying too much on bones to infer the movement behavior of animals, which is the impression she left when she watched the recent Commonwealth Games.

Bertrand laughed and said, "I've seen gymnasts do crazy things, and I think, it's funny, we have the same skeletal structure, and I can't do it." I think it's really interesting because maybe having that ability can help you survive, but from the bone you won't know if you have it or not. ”

Omnivorous foods bring survival advantages

Asteroids destroy most of the living plants on Earth, which are the lowest link in many food chains on Earth's land. Omnivorous mammals can eat any food and are more adaptable to the environment than animals that only eat certain special foods on a regular basis, so they have a better chance of survival.

Shelley said, "The animals that survived this mass extinction are basically not very special in their diet. "For example, Didelphodon, a close relative of a cat-sized carnivorous marsupial, preyed only on certain animals, but after the mass extinction it was intended to prey on became very rare. Shelley said, "The rat-toothed dragon's food was too simple, so it lost its own way of survival. However, if it is a small animal, it can change its diet and lifestyle more quickly to adapt to the environment. This is a great way to survive the mass extinction. ”

Brusart said that in addition to those animals that can eat anything can survive, there are a few animals with special eaters who also have an advantage, especially those that eat plant seeds are lucky. "Seeds are a food bank that doesn't dry up, and any animal that already feeds on seeds can also get seeds at the time of the mass extinction," he said. So, if an animal like a Tyrannosaurus rex is not so lucky, evolution does not have the ability to digest seeds for such animals. But for birds with beaks and some mammals that specialize in eating plant seeds, wow, is this the time to run? ”

In addition to maintaining the survival of the affected animals, plant seeds also help rebuild forests and vegetation after the nuclear winter disappears. Brussart said, "Seeds survive in the soil during the mass extinction, and when the sun comes again, these seeds will start to sprout and grow." ”

Long body does not grow brain

As the Paleocene passed, ecosystems recovered, and the earth was once again full of life, at which point mammals began to fill the void left by non-avian dinosaurs and became the strongest living species on Earth. Bertrand said, "Immediately after the extinction of the dinosaurs, mammals began to diversify their evolution, and there was a diversified development in either aspect." ”

First, the mammalian body rapidly enlarges. But the Edinburgh team found that changes in brain size in mammals can't keep up with how fast their bodies are getting bigger.

Bertrand said, "I think it's very important because we thought it might be intellectual development that allowed mammals to survive and eventually be able to rule the planet." But, from the data, it's not the brains that grow up to allow animals to survive asteroid impacts. ”

Mammals need their entire bodies to become larger and stronger in order to adapt to their environment

In fact, in the early Paleocene, mammalian brains, if too large, relative to the body, could be detrimental to survival. Bertrand asked, "The question is why do you need to grow a big brain?" In fact, too much brain size is quite expensive. If you have a large brain, you need to eat a lot to maintain it, and if you don't have enough food to do it, you will become extinct. ”

Instead, mammals need their entire bodies to become larger and stronger to adapt to their environment. In the hundreds of thousands of years after extinction, the herbivores of Ectoconus weighed about 100 kilograms. Pistodontariae are periptychidae animals that may be related to extant ungulate mammals. Hundreds of thousands of years in the geological epoch, just a blink of an eye. Shelley said, "It's really powerful for the outer cone beast to grow so big so quickly and develop a herbivorous habit so quickly." You see, once there are large herbivores, there are also large carnivores, and mammals begin to evolve rapidly. ”

There are many other mysterious mammalian bodies that also swell rapidly. Shelley said, "Animals like toothed beasts grow very fast and grow very large. "The complete skeleton of the toothed beast has not yet been found, but skull fossils have found that its skull is about the size of a large cream pumpkin, and the toothed beast seems to be one of the species that only became strong after the mass extinction to adapt to digging holes in the earth." Shelley said, "Its eye position is very small, the eye is also very small, but it has huge teeth in front, which is a bit like a rodent, but that's it." It's a very mysterious animal. ”

Shelley said these mammalian species, which evolved rapidly from the aftermath of the disaster, have long been ignored by the scientific community. The scientific community, she said, "thought they were ancient, primitive, and ordinary, but they weren't, they really had their own characteristics." Their ancestors survived the second mass extinction in the history of life on Earth, and they are by no means stupid animals that eat slowly. They survive and reproduce wonderfully. ”

These mammals in many ways filled the ecological space left by the tragic extinction of the dinosaurs. Highly personalized, giant dinosaurs were well adapted to the late Cretaceous environment, but lacked the ability to survive the catastrophe world after asteroid impacts.

"The most shocking thing is that we once had animals like dinosaurs on our earth, which survived for hundreds of millions of years and created such a great and glorious history, such as evolving themselves into behemoths the size of airplanes, and carnivores as big as buses, etc., but when the earth suddenly underwent great changes, these behemoths were completely extinct in an instant." Dinosaurs can't cope with new worlds, can't adapt to survival. ”

Asteroids that exterminated dinosaurs burst through the atmosphere faster than a bullet when they hit Earth (Credit: Nasa/JPL-Caltech)

The occurrence of asteroid impacts on Earth is highly random, which seems to have particularly impressed the university of Edinburgh research team that studies how mammals strove to survive after the mass extinction.

Bertrand said, "We humans are able to come into this world today mainly by luck. The asteroid that hits The Earth may pass by the Earth or fall into the oceans of another region of the Earth, either way, which will lead to different outcomes in the selection and evolution of future species of life. Whenever I think about the contingency of this whole thing, I think it's incredible. ”

Brusart felt the same way. "It's possible that an asteroid is only roaring away from Earth, that it may only churn up the upper layers of the atmosphere, or that it may disintegrate as it approaches Earth," he said. The asteroid had all sorts of possibilities, but it was a bad luck that it crashed straight into Earth. ”

But for the mammals living on Earth today, this catastrophe may be a godsend.