2024-04-21 13:27:29
The explosion burned forests to the roots, caused huge tsunamis and sent millions of tons of soot and dust into the atmosphere several kilometers high.
The meteorite destroyed the dominant animals of the planet – the dinosaurs (not all and not at once – but their population never recovered after this impact), and with them three quarters of all other species of flora and fauna that lived on the planet.
However, at the same time, the meteorite “spoiled” some small, inconspicuous mammals, which until then had mostly remained in the shadows – they could not compete with the dinosaurs and had not yet had time to grow fangs and claws.
Among the survivors was one very distant relative of ours, believed to be one of the first primates – the so-called purgatory (lat. Purgatory).
It could be said that it was something in between a small squirrel and a chipmunk – so it is very likely that it lived in caves, feeding on insects and whatever it could find, it was undemanding, inconspicuous and, by today’s standards, occupied the ecological niche of rodents.
“A rat will survive anywhere” – this is roughly the idea expressed by Steve Brusatti, the author of the book “The Rise and Reign of Mammals”, and his colleagues paleontologists from the University of Edinburgh, who decided to find out how early mammals were able to adapt so quickly and successfully to drastically changed living conditions .
Of course, the day of the apocalypse was terrible for all life forms, not just dinosaurs, but also other reptiles, fish, birds and mammals.
“It was not an ordinary asteroid, but the largest in the last half a billion years,” emphasizes S. Brusatti, “and mammals almost followed the dinosaurs.”
Sarah Shelley, a paleontologist at the University of Edinburgh, says mammals were surprisingly abundant at the end of the Cretaceous period. There were insectivorous mammals that lived in trees or caves – and strange creatures with sharp front teeth for eating fruit and nuts.
There were also small, cat-sized predators with fairly strong jaws designed to gnaw bones.
In the immediate aftermath of the meteorite impact, most of this diversity—nine out of ten mammal species—was lost. But the survivors faced unprecedented prospects.
“Imagine that you are one of our distant ancestors, a mouse-sized, small, timid animal, snooping around in corners,” says Brusatti. “And then comes a historic moment: all the tyrannosaurs and other giant lizards suddenly disappear, and the whole world opens up before you!”
But there was one “small problem”: together with the terrible dinosaurs, all the forests disappeared in a huge fire, the sky was black with soot, no light penetrated, photosynthesis stopped – in short, a real nuclear winter began. Ecosystems collapsed like houses of cards, the world suddenly became very unfriendly and even hostile.
What was the most important thing that mammals did then? The correct answer is that they didn’t get as big as the dinosaurs.
Less is better
At first, the small size of such mammals meant that they had to compete with dinosaurs – and they lost this competition in many ways – but suddenly it became clear that the lack of “emergency fauna”, as they were called, was actually a big – even vital – advantage.
“These mammals looked and behaved like mice or rats and would have remained invisible, but in the ‘brave new world’ they thrived because they were well adapted to the gruesome post-apocalyptic conditions,” says Brusatti.
Smaller animals found it easier to reproduce. As Ornella Bertrand, another paleontologist at the University of Edinburgh, points out, the larger modern animals are, the longer it takes them to bear fruit. For example, a female African elephant gives birth to a calf in 22 months – while a mouse’s pregnancy lasts only 20 days. Not surprisingly, mouse-sized animals have a much better chance of repopulating after a disaster.
Also, large animals take longer to reach sexual maturity, which is another reason why the dinosaurs, especially the large ones, became extinct.
“They took a long time to become adults: a tyrannosaurus took 20 years,” Brusatti explains. “And it’s not that they grew slowly, it’s just that many of them were huge, and it takes a long time to grow from a small baby to an adult dinosaur.”
Underground, but alive
Another key to the survival of mammals after the catastrophe may lie in the very strange structure of their bodies, from the Paleocene to somewhat later times.
According to S. Shelley, who compared the tibia bones of Paleocene and modern mammals (these small and very dense bones tend to preserve better than others), the bones of ancient mammals are very different, much more massive and stronger than those of today.
Post-apocalyptic animals had powerful muscles and strong bones that most closely resembled the bones of modern rodents.
“From this,” says S. Shelley, “the hypothesis arose that animals that were able to burrow underground successfully survived the catastrophe.” They survived the moment of the impact itself and the fires that broke out after it, then survived the nuclear winter and generally hid underground for a long time.”
The survivors were strong, and their offspring inherited these beneficial traits.
However, if these animals have indeed adapted to live underground in burrows dug by themselves or taken from others, O. Bertrand says that this could not have affected their mobility – and not for the better. Indeed, why does a caveman need the agility of a squirrel?
“We know that the forests disappeared overnight and all the animals living in the trees suddenly lost their habitat,” she emphasizes. “So one theory is that agility and flexibility have become redundant.”
Eating everything that moves and doesn’t move
The impact of the asteroid destroyed almost all land vegetation, which is the starting link of many food chains. Therefore, priority went to those mammals that were less picky about food: picky mammals simply died of starvation.
For example, Didelphodon, a cat-sized marsupial animal large enough to hunt smaller mammals of the time, did not change its diet after the disaster, lost its ecological niche, and became extinct.
“The animals that managed to survive the cataclysm did so mainly because they were not too attached to one food item,” says S. Shelley. “If you’re a small animal, it’s easier and faster to change your diet and lifestyle, which is a great survival strategy.”
But as S. Brusatti points out, sometimes narrow specialization also faced problems. For example, suddenly animals that had adapted to eating seeds were in huge trouble.
“Seeds were food reserves that any animal could feed on,” explains the scientist. “For example, if you were a tyrannosaurus, that’s where your luck ended – because evolution didn’t give you the ability to feed on seeds.” But if you were lucky enough to be born a bird with a sharp beak for reaching that food, or a mammal that specialized for that food, then Fortune smiled on you.”
And if at first the seeds helped the fauna to survive, then after the nuclear winter ended and the sun came out, new forests and all other vegetation grew from the seeds scattered by these animals. Thus the Earth was filled with new vegetation.
Less brain
The more time passed since the catastrophe, the more active the ecosystems became, and mammals began to occupy the niches previously occupied by dinosaurs.
“Mammal diversity began right after the dinosaurs went extinct, and it was diversity in every way,” says Bertrand. First of all, they began to grow, but scientists noticed one interesting feature: the brains of these mammals did not lag behind the growth of their bodies.
“This is very important to understand,” emphasizes O. Bertrand. – Because at first glance, one might think that it was the mind that helped us survive and later become the masters of the planet. But the evidence suggests that it wasn’t the brain that helped us survive the asteroid impact.”
In addition, early Paleocene mammals may have had large (relative to their body size) brains. “Why would you need a big brain, it’s too expensive to maintain,” explains O. Bertrand. “Someone with a big brain needs a lot of food – and if it’s not enough, the whole species just goes extinct.”
To adapt, mammals began to grow muscles instead of brains. Thus, the herbivorous ectocone, the likely distant ancestor of today’s ungulates, gained a solid 100 kg in just a few hundred thousand years (geologically, in an instant). Then the other herbivores started to gain weight, and so did the predators.
According to Shelley, scientists have for too long ignored this sudden increase in mammals that occurred immediately after the disaster. “They were called archaic, primitive, but really they were just different,” she says. “Their ancestors survived the second largest mass extinction in Earth’s history, and they weren’t idiots wandering the planet aimlessly!” No, they survived, they thrived – and they did it brilliantly.”
These mammals successfully filled many of the ecological niches left forever by the majestic, highly specialized dinosaurs, perfectly adapted to the late Cretaceous period – but completely unprepared for life in a post-apocalyptic world.
“It’s hard to imagine how dinosaurs, which lived for tens of millions of years, became giants the size of airplanes or predators the size of buses, were crushed at the same moment when the Earth changed dramatically,” says S. Brusatti. “They were underprepared for the new realities of life and were unable to adapt.”
All the more fantastic, according to Edinburgh scientists, is the scenario of further events. “We ended up on this planet by accident,” concludes O. Bertrand. “The asteroid could have passed by and landed in the ocean on another part of the planet, and then the selection of surviving animals would have been different.” When you think about it, you can go crazy.”
“It could have flown by, it could have hit only the upper layers of the atmosphere, it could have disintegrated on the way to Earth,” S. Brusatti says to her. “Anything could have happened to him, but it was only by chance that he flew straight to Earth.”
So, all the mammals living on our planet today can thank this asteroid a lot, according to the BBC.
2024-04-21 13:27:29