In the darkness, the ash cloud, and the deadly heat, the tiny furry animal makes its way through the inferno left after the worst day for living things in the history of planet Earth.
She picks through the rubble, catches an insect to feed herself, and quickly returns to the shelter.
All around her are the dead or dying bodies of dinosaurs that terrorized mammals for generations.
It was the early weeks and months after a 10-kilometer-wide asteroid slammed into the coast of present-day Mexico with a force stronger than billions of nuclear bombs, spectacularly ending the Cretaceous period.
At the dawn of the next era, the Paleocene, forests burned, tsunamis shook the coasts, and huge amounts of vaporized rock, ash, and dust rose kilometers into the atmosphere.
But this world was not completely devoid of life.
Among the survivors were the earliest known primates, the purgatorius, which looked like a cross between a shrew and a tiny chipmunk.
Their numbers have certainly declined in the midst of this global catastrophe, but the species has survived.
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Such was life for early mammals shortly after an asteroid struck and wiped out three-quarters of all living species on Earth.
Only the Great Dying, 252 million years ago, was more deadly (though less sudden), killing 95 percent of life in the oceans and 70 percent on land.
The asteroid that ended the Cretaceous period took with it famous dinosaurs such as tyrannosaurus and triceratops, as well as lesser-known but bizarre creatures such as the anzu, or "chicken from hell".
There were duck-billed dinosaurs, long-necked dinosaurs, armored dinosaurs all over their bodies - and, very soon, they were all dead.
In the shadow of these late Cretaceous kings and queens, mammals like Purgatorius were small and nimble, many of them filling the kind of ecological niches occupied by rodents today.
How did it happen that this diverse group of seemingly vulnerable creatures, including our ancestors, survived the end of the world?
That is the question that Steve Brusate, the author of the book, is working hard to answer The rise and reign of mammals, and his colleagues from the University of Edinburgh.
One thing Brusate keeps pointing out is that the day the asteroid hit was a very bad day to be alive as anything, including mammals, birds (avian dinosaurs) and reptiles.
"It was not a normal asteroid, it was the largest asteroid to hit the Earth in at least half a billion years," says Brusate.
"Mammals almost passed away like the dinosaurs."
A lot could have been lost.
The Late Cretaceous was already surprisingly diverse in mammals, says Sarah Shelley, a postdoctoral researcher in mammalian palaeontology in Edinburgh.
"Many of them were tiny insects that eat insects high up in trees or underground," says Shelley.
But not all of them were insectivores.
There were also the mysterious multituberculates, so named because of the unusual growths on their teeth.
"They had blocky teeth with many bumps on them, and the front tooth was like a blade. He looked almost like a saw," says Shelly.
"They ate fruits, nuts and seeds."
There were also carnivores - one of the largest of that time was the didelphodon, a relative of marsupials weighing about five kilograms, about the size of a domestic cat.
"Based on the head and the dental anatomy to conclude that it had a powerful bite, so it was definitely a carnivore - it probably could have broken bones," says Shelley.
Most of this diversity was lost when the asteroid hit—nine out of ten mammal species were wiped out, according to Brusate, providing an unprecedented opportunity for those who survived.
"Just imagine that you are one of our tiny ancestors, the size of small mice - a small, meek creature that hides in the shadows - and live through this moment in Earth's history," says Brusate.
"You get out of all that and suddenly there are no T-rexes, no long-necked dinosaurs, the world is full of possibilities."
This mass extinction set the stage for a major diversification boom that eventually brought blue whales, cheetahs, puffins, platypuses and, of course, us.
First, however, there was one small obstacle: the world's forests had disappeared in a massive fire and the sky was full of ash, blocking sunlight and preventing plants from photosynthesizing.
Ecosystems were collapsing "like a house of cards," says Brusate.
The surface of the Earth became hotter than an oven with severe heat waves, and this was followed by a nuclear winter in which average temperatures dropped by 20 degrees Celsius for more than 30 years.
Many of the most dangerous predators of mammals have disappeared, but the world itself has become unimaginably hostile to life in general.
So what did the mammals do?
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Stay small
The modest body size of mammals - previously limited by the competition and predation of dinosaurs - became an advantage for the "disaster fauna", as all those who survived the asteroid impact were known.
"These mammals were probably creatures that looked like mice or rats and behaved like that," says Brusate.
"They used to be pretty anonymous, but now, in this brave new world, they've started to reproduce because they've adapted so well to those really nightmarish conditions right after the impact."
Being small could have helped these animals rebuild their populations.
In modern animals, "the larger the animal, the longer the gestation period," says Ornella Bertrand, a postdoctoral researcher in mammalian palaeontology at the University of Edinburgh.
For example, an African elephant is pregnant for 22 months, while a mouse's pregnancy lasts about 20 days.
Faced with the apocalypse, the mouse has a better chance of increasing its population.
In addition to gestation, a larger body usually takes longer to reach sexual maturity - another reason why dinosaurs did not survive, especially the larger ones.
"It took them quite a while to grow up. Someone like the t-rex took 20 years," says Brusate.
"It's not that they didn't grow fast, it's just that there were a lot of them that were big so it took them a long time to hatch from the egg and grow into an adult."
Crawl underground
Another hint of how mammals survived the effects of an asteroid impact comes from the "highly twisted" body forms that can be found in the Paleocene and later.
Shelley analyzed ankle bones (small, hard, dense bones that are usually well preserved) to see how similar early Paleocene mammals were to each other and to mammals living today.
"We discovered that Paleocene mammals are really strange. They are different from modern mammals," says Shelley.
"And what they have in common is the fact that they have a very stocky, robust morphology."
"These mammals have large muscles and generally substantial bones, and are the most similar of living animals to subterranean or burrowing species," says Shelley.
"So the hypothesis that arose from this is that the animals that survived the extinction survived because they were able to burrow and crawl underground, survive the immediate post-impact period and the fires, the nuclear winter, and settle down for a while."
Because the surviving animals were - there's no other way to put it - leaner, and their offspring inherited their robust physiques.
"You can see that beautifully during that 10-million-year period in the Paleocene," Shelley says.
"Even if they're tree-dwelling animals, they're pretty stocky."
If the mammals really transitioned to life underground, by burrowing into it or using other people's underground shelters, Betran thinks that this could also be reflected in their mobility, or lack of it.
"We know that the forests were destroyed so that all those animals that lived in the trees no longer had a habitat," she says.
"And so, one hypothesis would be that fewer animals could engage in agile behavior."
Bertrand plans to examine the inner ear bones of mammals from this period to see if they support the idea of moving underground after an asteroid impact.
The inner ear is crucial for balance, so if the animal has adapted to harmonious, nimble movement, this is sometimes reflected in the structure of those delicate bones.
However, if they were stocky diggers, they wouldn't need such agility.
"That could give us more useful clues," she says.
However, she points out the downsides of relying too much on bones to find out how an animal moved, which became apparent to her while watching the recent Commonwealth Games.
"I was watching gymnasts achieve crazy things and I thought, look at that - we have the same skeleton, and I can't do any of that," laughs Bertrand.
"I thought, that's really interesting, because that ability might help you survive, but based on the bones, you wouldn't know."
Eat everything
The asteroid destroyed most living plants, the first link in many food chains on land.
Generalist mammals that had the ability to switch to anything else fared better than those with pickier diets.
"The animals that survived extinction survived basically because they weren't too specialized," says Shelley.
For example, didelphodon (a carnivorous relative of cat-sized marsupials) fed on animals that were absent after the mass extinction.
"It has become too specialized and lost its niche," says Shelley.
"Whereas, if you're a small animal, you can adjust your diet and lifestyle more quickly. It's a good way to survive extinction."
As well as those that could generalize, there were also a few specialized species that probably did well, says Brusate.
The seed eaters were especially lucky.
"Seeds were a food bank that was available to any animal that already had the ability to eat them," he says.
“So if you were like a t-rex, you were out of luck, evolution didn't gift you with the ability to eat seeds. But birds with beaks and some mammals that were specialized seed eaters, fate smiled on them."
In addition to keeping the "disaster fauna" alive, the seeds helped regrow forests and other vegetation once the nuclear winter subsided.
"That seed survived in the soil and then, when the sun shone again, it started to grow again," says Brusate.
Don't overthink it
As the Paleocene wore on, ecosystems recovered and mammals began to fill the holes left behind by non-avian dinosaurs.
"Mammals started to diversify immediately after the dinosaurs died out and they started to be very diverse in every possible way," says Bertrand.
First of all, their bodies got bigger very quickly.
But for a while, the Edinburgh team found, the size of the mammal's brain didn't keep pace with the growth of the rest.
"I think it's very important, because we tend to think that intelligence is what helps us survive and dominate the planet," says Bertrand.
"But based on our data, it wasn't the big brain that helped animals survive the asteroid impact."
Moreover, in the early Paleocene mammals with large brains in relation to their body size may even have been left behind.
"The question is, why would you grow a big brain in the first place?" Bertrand asks.
“A big brain is usually expensive to maintain.
"If you have a big brain, you have to feed it to maintain it, and if you can't because there isn't enough food, you die out."
Instead, being big and muscular was a more desirable adaptation.
The herbivorous ectoconus (a member of the periptychids, which could be related to today's ungulates) reached about 100 kilograms within a few hundred thousand years after the mass extinction.
In geological terms, it's the blink of an eye.
"It's crazy that they got so big so fast and specialized so quickly," says Shelley.
"And, you see, once you get the bigger herbivores, you get the bigger carnivores, and they start showing up pretty quickly."
There are many other mysterious mammals that also grew rapidly.
"Creatures like the teniodonts — they got big quickly, pretty big," says Shelley.
There are no complete teniodont skeletons, but the skull was the size of a nutmeg and they seem like one of those species that became bulky and adapted for digging.
"It has tiny places for little round eyes and massive teeth in the front, which kind of resemble rodents, but that's about it," says Shelley.
"They are a real enigma."
This rapid menagerie of mammalian life that resulted from the "faunal catastrophe" has been neglected for too long, says Shelley.
"They call them archaic and primitive and generalized - when really they're just different," she says.
"Their ancestors survived the second largest mass extinction in the history of life. They weren't just generalized morons stumbling through life.
"They were surviving and evolving and doing it very well."
In many ways, these mammals filled the ecological voids left by the majestic, hyper-specialized dinosaurs so well adapted to the late Cretaceous but so fundamentally ill-equipped to cope with an asteroid-stricken world.
"It's amazing to think that you had a group like the dinosaurs, that was around for tens of millions of years, that achieved such magnificent things as growing into giants the size of airplanes, and carnivores the size of buses, and all these kinds of creatures - and then everything just collapsed in a second when the Earth changed overnight," says Brusate.
"They were ill-equipped for that new reality and couldn't adapt."
The arbitrariness of this event is something that particularly impresses the team from Edinburgh.
"We are here by chance," says Bertrand.
"An asteroid could have missed Earth, it could have hit an ocean in another area of the planet and that would have made a difference in terms of which species were selected to survive."
"When I think about it all - it's crazy."
Brusate agrees.
“It could have brushed past us, it could have just skimmed the upper atmosphere, it could have disintegrated as it got closer to Earth.
“He could have done any of those things, but by sheer chance he made his way straight to Earth.
For mammals alive today, it may be a good thing he did.
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