Last suffered, too, of course. But, younger, she had more strength to spend. Purga was aware of a growing distance between them. It was not a question of disloyalty. This was the logic of survival. Purga sensed, deep down, that the day would come when her daughter would see her not as a foraging companion, not even as a hindrance, but as a resource. After all she had survived, maybe Purga’s final memories would be of her own daughter’s teeth at her throat.

But now they smelled meat. And they saw more survivors, more ratlike mammals, scurrying across the beach. There was something to be had. Purga and Last struggled to follow.

At last, her awareness flickering like a failing lightbulb, the great euoplo stumbled to the shore of the ocean.

She looked down, uncomprehending. Water lapped at her feet, dappled by heavy raindrops. The sand was flecked with the black of soot and volcanic dust, and littered with the bones of tiny creatures. She made out the silvery bodies of fish, lifeless, their eyes pecked out by opportunistic birds. But the euoplo knew only her own weariness, hunger, thirst, loneliness, pain.

She raised her head. The sun, setting to the southwest, was a disk, bloodred, not far above a horizon that was charcoal against charcoal.

The euoplo stood motionless at the edge of the water. She was one of the last large dinosaurs left alive anywhere on Earth, and she stood now like a statue to her vanishing kind. Her head and tail felt very heavy, weighed down by all that armor. She let them droop. She was dying without ever having produced a single viable young. An abject misery clamored within the euoplo’s small consciousness.

There was a sharp nip at the pad on the base of her foot.

It was a therian mammal. It was no more prepossessing than Purga, and yet equipped with teeth that scissored — just as, one day, a lion’s would. It had run forward and bit her, with absurd boldness. The euoplo hooted her indignation. With a vast effort, she raised one immense foot. But when she slammed it down into the water she made only a splash; the scurrying mammal escaped.

But, all around her, more survivors gathered.

None of these animals were large. Purga and Last were here, and other mammals, little ratlike creatures that had kept themselves alive in their underground burrows, warmed through this long winter by their constant body heat. There were birds, protected by their hot blood and small size from an event which their more spectacular relatives could not endure. Here, too, were insects, snails, frogs, salamanders, snakes, creatures who had endured in burrows and riverbanks or deep holes. These small, scurrying creatures had been used to feeding off scraps and hiding in the corners anyhow; to them, the comet impact hardly made things worse.

Now they moved closer to this giant, the last of the monsters who had dominated their world for a hundred million years. In the long empty months since the impact, as they spread out through a world like a charnel house, many of them had learned to exploit a new food source: dinosaur flesh.

Times had changed.

Extinction was a terminus more drastic than death.

At least with death there was the consolation that your descendants would go on after you, that something of your kind would linger on. Extinction took away even that comfort. Extinction was the end of your life — and of your children, and all your potential grandchildren, or any of your kind, on to the end of time; life would go on, but it would not be your kind of life.

Dread though they were, extinctions had always been commonplace. Nature was packed thick with species, each connected to all the others through competition or cooperation, all endlessly struggling for survival. Though nobody could get permanently ahead, it was possible to fail — through bad luck, or disaster, or invasion by a better-equipped competitor — and the price of failure had always been extinction.

But the comet impact had now triggered a mass extinction, one of the worst in this battered planet’s long history. Dying was occurring in every biological realm, on land, in the sea, and in the air. Whole families of species, whole kingdoms, were falling into the darkness. It was a huge biotic crisis.

At such a time it didn’t matter how well adapted you were, how well you evaded the predators or competed with your neighbors, for the most basic ground rules were changing. During a mass extinction, it paid to be small, numerous, geographically widespread, to have somewhere to hide.

And, crucially, to be able to eat other survivors in the aftermath.

Even then survival depended as much on good fortune as good genes: not evolution, but luck. For all their smallness and ability to hide, more than half the mammals had gone extinct with the dinosaurs.

But the mammals owned the future.

The euoplo was not aware of her legs collapsing. But there was suddenly a damp cold under her belly, a gritty saltiness in her mouth where her head dangled into the water.

She closed her eyes. The heavy armor made the lids opaque. She rumbled deeply — a sound that another of her kind could have heard kilometers away, had there been any to hear — and tried to spit the brine out of her mouth. She retreated into her bony armor, like a turtle inside its shell. Soon it was as if she could no longer hear the hiss of rain on the sand and water, the scuffling of the ugly little creatures who surrounded her.

Even to the last she knew no peace, only a huge reptilian loss. But she felt little pain, when the small teeth went to work.

This last great dinosaur was a storehouse of meat and blood that fed the squabbling horde of animals for a week.

At the end of that time, as the acid rain began to leach the huge gnawed plates of the euoplo’s back gleaming white, Purga and Last encountered another group of primates. There were several of them, mostly about Last’s age or younger — so they had probably been born after the impact, and had known nothing, all their lives, but this straitened world. They looked lean, hungry. Determined. Two of them were male.

They smelled strange. They were not even distantly related to Purga’s family. But they were undoubtedly Purgatorius. The males had no interest in Purga; her subtle scent told them she was too old to bear any more litters.

Last gave her mother a final glance. And then she scampered over to the others, where the males, whiskers quivering, began to sniff her and to nuzzle her with bloodied snouts.

After that day Purga never saw her daughter again.

A month later Purga, wandering alone, came upon the carpet of ferns.

Entranced, Purga hobbled forward as fast as she could. These were only lowly groundcover growths, but their fronds made a dim green shade. On the underside she could see little spore sacs, brown dots.

Green, in a world of soot and ash gray.

Ferns were robust survivors. Their spores were tough enough to withstand fire, small enough to be carried great distances on the wind. In some cases the new growths sprouted directly from surviving root systems, black, creeping roots that were far more indestructible than the roots of trees. In times like this, as the light slowly recovered and photosynthesis became possible, the ferns faced little competition. Amid the muddied ash and clay, the world was taking on a look it had not had since the Devonian age some four hundred million years before, when the first land plants of all — primitive ferns among them — had made their tentative colonies.

She climbed. The tallest of these ground huggers gave her a platform just a few centimeters off the ground, but she clambered onto the fronds gratefully. It was enough to release in her a flood of inchoate memories of how she had scurried along the branches of the great, vanished Cretaceous forests.