The night after that the male found her again, having tracked her scent. He still stank of her dead babies, of the lost part of her. She fought him off savagely.

It took her two more nights before she accepted his courtship. Soon her body would begin to incubate his young.

It was hard.

It was life.

It would have been of no consolation to Purga to know that this brutal landscape, which had swallowed up two of her broods, would soon be overwhelmed by a wave of suffering and death to dwarf anything she had endured.

Earth was now inside the comet’s swelling coma, the loose cloud of gases that swathed the nucleus itself.

All over the night side of Earth the tail could be seen stretching away from the sun. It was as if the planet had drifted into a sparkling tunnel. The sky glittered with meteors, tiny bits of comet falling harmlessly into the high atmosphere, creating a light show glimpsed by uncaring dinosaurs.

But the comet’s nucleus was bigger than any meteor. It moved at twenty kilometers per second, at interplanetary speeds. It had already crossed the orbit of the Moon.

From where it would take just five more hours to reach Earth.

All night long, the birds and pterosaurs sang their confusion; during the day, they slumped with exhaustion. There was no room in their neural programming for a new light in the sky, and they were disturbed at a deep cellular level. In the shallow seas, too, the unending light had disturbed the plankton and larger creatures like crab and shrimp; the cynical hunters of the reef fed well.

Only the great dinosaurs were unperturbed. The comet light made no difference to the air temperature, and when true night had fallen they slipped into their usual torpor. On the last night of a reign that had lasted nearly two hundred million years, the rulers of the Earth slept untroubled.

If not for the tyrannosaur eggs, the young giganotosaur would have spotted the disturbed troodon earlier. In the lee of the mountains, he stalked silently through the green shadows. His name meant Giant.

The forest here was sparse, spindly araucaria and tree ferns, scattered over a ground littered with sharp-edged volcanic rocks. Nothing moved. Anything that could hide had already hidden; anything else lay still, hoping for the shadow of death to pass by.

He came to a pile of moss and lichen. Superficially it looked like a heap of debris piled up at random by wind or the passage of animals. But Giant recognized the characteristic scrapings, the lingering smell of meat eater.

It was a nest.

With a rumble of anticipation, he fell on the nest and began to dismantle it with his stubby forearms. When he had exposed the eggs, Giant dug his clawed thumb, with a surgical precision, into the top of the largest. He pulled out the embryo head first. As the mucus and yolk drained from it, lurid colors bright, Giant saw the chick squirm feebly, even saw its tiny heart beat.

Just as the embryos of chimps, gorillas, humans would all be disturbingly similar, so dinosaur fetuses all looked alike. There was no way to know that this chick would have been a female tyrannosaur. Blind, deaf, immature, the embryo struggled to open her mouth, dimly imagining the hulking shape of a mother who would feed her. Giant flicked the embryo into his mouth and swallowed it without chewing. The chick’s life ended in crushing, acidic darkness.

It didn’t matter. Even if no predator had come this way, her egg would have been destroyed before she could have hatched by a monster even more terrible than a giganotosaur.

Giant was descended from South American stock that had crossed a temporary land bridge into this continent a thousand years earlier.

In a world of slowly separating island continents, the dinosaur fauna had become diverse. In Africa there were archaic-looking long-necked giant herbivores and creatures like hippos with fat, low-slung bodies and powerfully clawed thumbs. In Asia there were small, fast-running horned dinosaurs with noses like parrots’ beaks. And in South America large sauropods were hunted by giant pack-hunting predators; there it was like a throwback to earlier times, to Pangaea. The giganotosaurs had cut their evolutionary teeth hunting the great South American titanosaurs.

Giant was an immature male, and yet he already outmassed all but the very largest carnivores of the era. Giant’s head, in proportion to his body, was larger than a tyrannosaur’s — and yet his brain was smaller. The giganotosaurs were less agile, less fast, less bright; they had more in common with the ancient allosaurs, equipped to kill with teeth and hands, whereas the tyrannosaurs, all their evolutionary energy funneled into their huge heads, specialized in immense, sharklike bites. Where the tyrannosaurs were solitary ambush hunters, the giganotosaurs were pack animals. To bring down a sauropod fifty meters long and weighing a hundred tons, you didn’t need brains as much as raw strength, rudimentary teamwork — and a kind of reckless frenzy.

But, coming across that land bridge into a new country, the giganotosaurs had been forced to confront an established order of predators. The invaders had quickly learned that their takeover of a region could not succeed unless they first mounted a bloody coup against the ruling carnivore.

Which was why this young male giganotosaur was munching slippery tyrannosaur embryos. Resolutely Giant cracked one egg after another. The carefully constructed nest turned into a mess of shattered eggs, scattered moss, and chunks of dismembered chick. Giant was feeding well — and issuing a challenge.

It would be a transfer of power. The tyrannosaur had been the top predator, mistress of the land for a hundred kilometers around, as if the whole elaborate ecosystem was a vast farm run for her benefit. The prey species had come to terms with the formidable presence that lived amongst them: with their armor or weapons or evasive strategies, each of the hunted had reached a point where their losses to predators were not a threat to the endurance of the herd.

Given time, all that would have changed. The impact of the invaders’ hunger would have rippled down the food chain, disturbing creatures large and small, before a new equilibrium could be established. It would have taken longer still for the prey species to learn new behaviors, or even evolve new coping systems or armor to deal with the giganotosaurs.

But none of that would happen. There would not be time for the giganotosaur clan to exploit their triumph. Not in the few hours left.

The nest destroyed, Giant wandered away. He was still hungry, as always.

He could smell putrefaction in the still, misty air. Something huge had died: easy meat, perhaps. He pushed through a bank of tree ferns and emerged into another small clearing. Beyond, through a screen of greenery, he could dimly see the black flank of a young volcanic mountain.

And there, in the middle of the clearing, was a dinosaur — a troodon — standing quite still above a scraping of earth.

Giant froze. The troodon had not seen him. And she was alone; there were none of the watchful companions he associated with the packs of this particular agile little dinosaur.

There was something wrong with the way she was behaving. And that, so the grim predatory calculus of his mind prompted him, gave him an opportunity.

Wounding Tooth should have been able to overcome the loss of a clutch of eggs.

This was a savage time, after all. Infant mortality rates were high; and at any time of life, sudden death was the way of things. This was the world the troodon had been evolved to cope with.

But she could not cope, not anymore.

She had always been the weakest of her brood. She would not even have survived the first days after her hatching if not for the chance decimation of her siblings by a roaming marsupial predator. She had grown to overcome her physical weakness, and had become an effective hunter. But in a dark part of her mind she had always remained the weakest, robbed of food by her siblings, even eyed as a cannibalistic snack.