Evolution Read online

  The moth quickly died, its sparklike awareness incapable of recording much pain.

  The moth consumed, Purga moved on. There was no grass cover here — the grasses had yet to dominate the land — but there was a green covering of low ferns, mosses, ground pine, horsetails, and conifer seedlings, even a few gaudy purple flowers. Through this tangle, scuttling between scraps of cover, she was able to progress almost silently. In the dark, solitary foraging was the best strategy. Predators worked by ambush, exploiting the shadows of the night; no group could have been as invisible as a lone prowler. And so Purga worked alone.

  To Purga the world was a plain picked out in black, white, and blue, lit up by the uneasy light of the comet, which shone behind high scattered clouds. Her huge eyes were not as sensitive to color as the best dinosaur designs — some raptors could make out colors beyond anything that would be visible to humans, somber infrareds and sparkling ultraviolets — but Purga’s vision worked well in the low light of night. And besides she had her whiskers, which fanned out before her like a tactile radar sweep.

  Purga looked more rodentlike than primate, with whiskers, a pointed snout, and small folded-back ears. She was about the size of a small bush baby. On the ground she walked on all fours, and she carried her long bushy tail behind her, like a squirrel. To human eyes she would have seemed strange, almost reptilian in her stillness and watchfulness, perhaps incomplete.

  But, as Joan Useb would one day learn, she was indeed a primate, a progenitor of that great class of animals. Through her brief life flowed a molecular river with its source in the deepest past, its destination the sea of the furthest future. And from that river of genes, widening and modifying as thousands of millennia passed, would one day emerge all of humanity: Every human ever born would be descended from the children of Purga.

  She knew none of this. She didn’t give herself a name. She was not conscious like a human — or even like a chimp or monkey; her mind was more like a rat’s or a pigeon’s. Her behavior was made up of fixed patterns, controlled by innate drives that constantly shifted in balance and priority, reaching a new sum each moment. She was like a tiny robot. She had no sense of self.

  And yet she was aware. She knew pleasure — the pleasure of a full belly, the safety of her burrow, the snouts of her pups as they nuzzled her belly for milk — and, in this dangerous world, she knew fear very well.

  She crept among the feet of dreaming ankylosaurs. As she moved beneath the immense bellies Purga could hear the huge rumble of the dinosaurs’ endless digestion, and the air was thick with their noxious farts. With their crude teeth, all the work of processing and digesting their coarse food had to be done in the dinosaurs’ vast guts, which labored even as the ankylosaurs slept.

  The ankylosaurs were herbivorous dinosaurs. But this was a time of huge, ferocious predators. So these animals, larger than African elephants, were covered with armor, a fusion of bones, ribs, and vertebrae. Great yellow-black spines were embedded in their backs. Their skulls were so heavily reinforced there was little room left for brain. Their tails ended in heavy clubs that could smash legs or skulls.

  The dinosaurs were too huge for Purga to comprehend. Hers was a small world, where a fallen log or a puddle was a major obstacle, where a scorpion could be a significant predator, where a fat millipede was a rare treat. To her, the dozing ankylosaur herd was a forest of immense stumpy legs and drooping tails that had no connection to each other.

  But for Purga there was a rich prize here: dinosaur dung, immense heaps of it scattered in the muddy, trampled ground. Here, in fibrous mountains of roughly digested vegetation, she might find insects, even dung beetles, laboring to destroy the tremendous turds. She burrowed into the steaming stuff eagerly.

  Thus had been the role of the ancestors of humanity, all through the long dinosaur summer: relegated to the fringe of the reptiles’ great society, emerging from their burrows only at night, foraging for a living from dung, insects, and the small pickings of the forest.

  But tonight the rewards were meager, the droppings watery and foul-smelling. The volcano-damaged vegetation had provided poor fodder for the ankylosaurs, and what came out the other end was of little value to Purga.

  She moved across the clearing and into the forest. Here conifers towered grandly, rising to spreading mats of leaves far overhead. Among them were smaller trees a little like palms, and a few low bushes bearing pale yellow flowers.

  Purga scrambled briskly into the angular branches of a ginkgo tree. As she climbed she used the scent glands in her crotch to mark the tree. In her world of night, scent and sound were more important than sight, and if others of her kind found this mark, any time within the next week, it would be a sign like a neon light, telling them she had been here, even how long ago she had passed.

  It was pleasing to climb, to feel her muscles work smoothly as they hauled her high above the dangerous ground, to use the delicate balance afforded by her long tail — and, most of all, to jump, to fly briefly from one branch to another, using all her body’s equipment, her balance, her agility, her grasping hands, her fine eyes. She was forced to shelter in burrows on the ground. But everything about her had been shaped by an existence in the complex three-dimensional environment of the trees, where almost all primate species, throughout the family’s long history, would find refuge.

  But the acid rain of recent months had withered the trees and undergrowth; the bark was sour, and there were few insects to be found.

  Purga was perpetually hungry. She needed to consume her body weight every day: It was the price of her warm blood, and the milk she must produce for her two pups, safe in their burrow deeper in the forest. She clambered reluctantly back down the trunk of the ginkgo. Fear and hunger warring in her mind, she tried one or two more trees, but with no better luck.

  But now she lifted her head, whiskers twitching, bright eyes wide, to peer into the green dark of the forest. She could smell meat: the alluring stench of broken flesh. And she heard a forlorn, helpless piping, like that of baby birds.

  She scuttled away, following the scent.

  In a small clearing at the base of a huge, gnarly araucaria there was a heap of roughly piled moss. At its edge, a small patch of debris-littered silt began to move. Soon the patch rose like a lid, and a small, scrawny neck poked out of the ground and through the layer of mud and debris. A beaklike mouth opened wide.

  Its little head quivering, tiny scales and feathers still moist with yolk, the infant dinosaur took its first breath. It looked like an oversized baby bird.

  It was the moment the didelphodon had been waiting for. This mammal, the size of a domestic cat, was one of the largest of its day. It was low slung, with a black-and-silver coat. Now it lunged forward and grabbed the chick by its thin neck, hauling it from its shell and flinging it into the air.

  The chick’s life was a handful of brief, vivid impressions: the cold air beyond its cracked shell, the blurred glow of the comet, a sense of flying. But now a hot cavern opened beneath it. Its skin still smeared with yolk, the chick died instantly.

  Meanwhile more chicks were pushing out of the ground, hatching all at the same time. It was as if the ground were suddenly swarming with baby dinosaurs. The didelphodon, and more predatory mammals, closed in to feed.

  An ancient survival strategy had been operating. Dinosaurs were reptiles who laid their eggs on the ground. Though some parents stayed with their brood, there was no way all the vulnerable eggs and chicks could be protected. So dinosaurs laid many eggs, and their hatchings were synchronized. There should have been dozens of broods hatching right now, scattered through this area of forest: hundreds of chicks. The idea was that suddenly the forest floor would be overwhelmed with baby dinosaurs, far too many for even the hungriest of predators. Most of the chicks would die, but that didn’t matter. It was enough that some would survive.

  But here, tonight, the strategy had gone wrong — horribly so for the dinosaur chicks. The mother of these chicks was a hu
nter isolated from her pack. Confused, hungry, scared of predation herself, she had laid her eggs in the old, familiar place — this rookery was millennia old — and covered them with rotting vegetation for warmth. She had done just what she should have done, save that it was the wrong time, and the eggs had been forced to hatch without the cover of hundreds of others.

  The air was filled with the stink of blood, the low growls of the predators, and the sad peeping of the doomed chicks. There were many species of mammals represented here at this grisly banquet. The largest was the big didelphodon. There was a pair of deltatheridiums, ratlike omnivores, neither marsupial nor placental, a unique line that would not outlive the dinosaurs. Many of the creatures here had potential far beyond their present standing; one unprepossessing little creature was an ancestor of the line that would lead to the elephants.

  But for now, all that concerned them was their empty bellies. Dissatisfied with the slow emergence of the struggling hatchlings, the mammals had already started to dig into the loose silt, seeking unbroken eggs, scattering the cover of moss laid over the nest by the mother dinosaur.

  By the time Purga arrived the rookery had become a killing pit, a squirming mass of feeding mammalian bodies. Purga, late to the fray, burrowed eagerly into the dirt. Soon tiny bones crunched in her mouth. And, so deeply did she immerse her head in search of the deep-buried goodies, she was the last to sense the return of the mother dinosaur.

  She heard an angry bellow, felt the ground shudder.

  Her snout sticky with yolk, Purga pulled her head out of the dirt. The other mammals were already vanishing into the forest’s welcoming green black. For one instant Purga saw the whole creature, an unlikely feathered monster suspended in the air, limbs splayed, mouth gaping. Then a vast clawed hand flashed out of the sky.

  Purga hissed and rolled. Too late she learned that this was the nest of a troodon: an agile, fast-moving killer — and a specialist hunter of mammals.

  The troodon’s name meant “Wounding Tooth.”

  Wounding Tooth, the size of a dog, was not the largest of dinosaurs, but she was intelligent and agile. Her brain compared in size to that of the flightless birds of later eras she somewhat resembled. Her eyes were as large and as well night-adapted as Purga’s, and they could see forward, giving her binocular vision, the better to triangulate on her small, fast-moving targets. She had legs that enabled her to spring like a kangaroo, a long sicklelike claw on the second toe of each foot, and hands like spades evolved specifically to dig out and crush scuttling mammals.

  She was coated in small sleek feathers, an elaborate development of scales. The feathers weren’t meant for flying, but for warmth during the night’s chill. In the equable climate that swathed the Earth in these times, you didn’t need a hot-blooded metabolic engine to keep warm: If you were big enough, your cold-blooded body would retain its heat right through the night, even if you lived at Earth’s extremes, at the poles. But smaller dinosaurs, like the troodon, needed a little extra insulation.

  Small or not, she had one of the largest brains of all dinosaurs. All in all, she was a well-equipped hunter. But Wounding Tooth had problems of her own.

  She could not know it, but they had been caused by the widening of the Atlantic, the huge geological event that had dominated the whole of this Cretaceous period. As the Americas were pushed west, North America’s huge inland seaway had shallowed and drained, and close to the western coast — just a few hundred kilometers from the troodon’s hatching site — that line of new volcanoes had erupted like an angry wound. The volcanism had disturbed the complex web of life in many ways. The young volcanoes were almost continually active, belching out smoke and ash ladened with sulfur that, mixing with the rain, turned to acid. Many species of plants had vanished, and trees on the higher ground had been reduced to bare trunks. Elsewhere the destruction had been more direct, with vast fingers of cold lava reaching deep into the forest.

  The troodon’s mammalian food, relatively close to the base of the food chain, had been less disturbed than most of the larger species of predatory dinosaurs. In fact, with their tiny bodies, deep burrows, and fast reproductive rate, the mammals were better equipped to live through such times of stress than the land’s grander overlords.

  But troodons were pack hunters. And this female had, some days ago, become isolated from her pack by a spectacular venting of hot steam from a fissure. Even though she was alone, Wounding Tooth was carrying eggs from her last fertilization. So she had come to the herd’s ancient roosting site. A deep part of her had hoped to find others of her kind here. But there was no other here, only herself.

  Wounding Tooth was growing older. At fifty, she found many of her much-stressed joints were racked with the pain of arthritis. And, because of her age and loss of strength and flexibility, she herself was under threat: This was, after all, a time of predators powerful enough to justify armor plating on creatures bigger than elephants. She had to reproduce; every instinct demanded it.

  She had laid her eggs, as she had before. What else could she do?

  The nest itself was a circular pit scraped out of the dirt, and she had arranged the eggs with an odd, almost surgical precision. She made sure the twenty eggs were not too close together, and that the top of each elongated egg pointed to the center so the emerging chicks would have a good chance of digging their way out. Then she had covered over the eggs with dirt and moss. She had returned several times to the nest, probing with her claws to tap the shells. The eggs had developed well; she could see it. But now the eggs had hatched — her young had emerged — but nothing was left of them except scattered bits of red flesh and gnawed bone. And here, in the center of the smashed nest, was a mammal, her face stained by blood and yolk and dirt.

  Which was why Wounding Tooth leapt.

  Purga helplessly squirted urine and musk, leaving a scent warning: Beware! Mammal hunter about! Then she ran out of the forest, back to the clearing of the ankylosaurs.

  But on the edge of the clearing Purga hesitated. She had a choice to make, a choice of dangers. She had to get away from the pursuing troodon. She was heading back toward her burrow, where her pups waited. But by crossing the clearing again she was leaving the safety of the trees. The unconscious calculus rapidly produced a result. She took the gamble; she raced across the clearing.

  A sleepy infant giant raised one bony eyelid.

  The light seemed brighter than ever now, exposing Purga clearly. But there was no dawn; it was only the comet, its nucleus huge, blurred, and bright, the gas jets that erupted from it clearly visible, even through the haze of air. It was an eerie, extraordinary sight that sparked a dim curiosity in her agile mind, even as she ran.

  A shadow fled at the corner of her vision.

  Instinctively she darted sideways — just as a dinosaur hand slammed into the ground where she had stood. She ran back into the ankylosaur herd, darting this way and that, seeking cover in the shadow of the lethargic dinosaurs.

  The troodon chased her around immense legs. But even the enraged mammal hunter was reluctant to disturb these huge armored beasts. Their clubbed tails could have crushed her in a second. Purga even slithered perilously under one ankylosaur’s huge raised foot, which hovered like a falling moon above her, while Wounding Tooth, frustrated, hissed and scraped at the ground.

  At last Purga reached the far side of the clearing. Her scent and instinct guiding her unerringly, she raced into the undergrowth.

  Her burrow was pitch dark, too dark even for her huge eyes to make out anything. It was like entering a mouth set in the warm earth. But the burrow was full of the consanguineous smell of her family, and she could hear the snuffle of her two young as they squirmed blindly out of the dark. Soon their warm, tiny mouths were nipping at her belly, seeking her nipples. Her mate was not here; he was out foraging himself in this clear Cretaceous night.

  But Wounding Tooth must be close; the scent of warm flesh, fur, and milk that had helped bring Purga home would draw the hu
nter here too.

  The imperatives in her head shifted again. She tucked her infants behind her and pushed her way to the back of the burrow, away from its entrance. Purga, unlike the troodon, was young — just a few months old, in fact — and this was her first brood. And unlike the prolific dinosaurs, Purga’s kind bore few young. She could not afford to lose her brood. And now she prepared to fight for them.

  There was a crash behind her.

  The roof of packed earth imploded, showering Purga and the pups with dirt. Comet light flooded in, startlingly bright after the few seconds of darkness. It was as if a bomb had fallen. A huge grasping hand reached out of the sky into the burrow. The pups squirmed and squealed, but one of them was impaled on a bloody claw. In an instant its life was over. It was lifted up and out of the burrow, a naked, lifeless scrap, and out of Purga’s life.

  Purga hissed her distress. She ran toward the burrow entrance, away from the claw. She could sense the remaining infant, naked and stumbling, hurrying after her. But the wily troodon had foreseen this. That claw now pushed into the entrance, breaking open its earthen walls. Reptile fingers closed, and the second pup’s life was squeezed out, its skull and tiny bones crushed, its organs pulped.

  Purga, her world broken apart in a few heartbeats, scrabbled away from the debris of the entrance, away from the broken roof, back to the deepest recesses of the burrow. But again and again that machinelike clawed paw slammed through the roof, breaking it down and admitting more milky comet light.

  Purga’s body urged her to flee, to find darkness, a new burrow, shelter — to be anywhere but here. She was even hungry; for such a fast-metabolizing creature as Purga, it had been a long time since she had supped the yolk of Wounding Tooth’s eggs.

  But suddenly the strength drained out of her.