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incomprehensible activities in the world of day above. The ground would shake as if in an earthquake, and bits of the burrow walls crumbled and fell around the dozing family. It was as if the world was full of walking skyscrapers.
    But there was nothing to be done about any of that. To Purga the dinosaurs were a force of nature, as beyond her control as the weather. In this huge, dangerous world, the burrow was home. The thick earth protected the primates from the heat of the day, and sheltered the still-naked pups from the night’s chill: The earth itself was Purga’s shelter against dinosaur weather.
    And yet, at the back of her small mind, there was a tiny chapel of memory, a reminder that this was not her first home, not her first family— a lingering warning that she could lose all this, too, in another instant of light and flashing claws and teeth.

    • • •
    When the Earth turned and the air cooled and the dinosaurs settled into their nightly torpor, at their feet the dirt stirred. The creatures of the night emerged: insects, amphibians— and many, many burrowing mammals, rising like a tide of miniature life around the dinosaurs’ pillarlike legs.
    This night Purga and her new mate traveled together. Purga, a little older and more experienced, led the way. A few centimeters apart, proceeding in cautious fits and starts, they made their way down the shallow slope toward the lake.
    They did not usually forage together. But the weather had been dry, and the priority for both of them was to get a drink.
    This part of America had endured a long, epochal drying. Here the relic of the ancient inland sea was a great stretch of swampy land, drowned by new sediment from the Rockies to the west, young mountains eroding almost as quickly as they were born. And in this time of relative drought, any standing water was a focus for animals large and small.
    And so the lakeshore was crowded with dinosaurs.
    Here was a herd of triceratops, three-horned giants with huge bony frills that covered their shoulder regions. They were like heavily armed rhinos, dozing in their loose circles, the adults’ ferocious horns pointing outward to deter any hungry, night-prowling aggressor.
    There were many duck-billed hadrosaurs. Herds had gathered around this shallow lake, a bewildering, brightly colored array of them, and Purga and Second had to creep past forests of their great, immobile legs, like refugees in an immense sculpture park. Even now, as the duckbills slumbered, their unconscious snoring was a cacophony of deep and mournful hoots, honks, and cries; they sounded like fogbound ships.
    At last Purga and Second reached the edge of the lake. The water had receded, and they had to cross a stretch of stony, half-dried pond-bottom mud, slick with mucus and sheets of green vegetation. In the eerie, still light, Purga drank quickly, her eyes wide and whiskers twitching.
    Their thirst sated, the primates split up. Second began to track over the shallow beach, looking for the little piles of coiled sand that marked the presence of a worm.
    Purga moved up the beach to the fringe of the scrub, following a more intriguing smell.
    She soon found the source of the stink: a fish. It was lying in a heap of rusty fern fronds, its carcass shriveled within its silvery skin. Somehow stranded far from the water, it had been dead many hours. When Purga poked the fish’s skin it burst, releasing a voluminous, noxious stench— and a squirming mass of ghost-pale maggots. Purga plunged her paws into the carcass. Soon she was pushing maggots into her mouth; the salty goodies burst between her teeth, releasing delicious body juices.
    But now another fish came flying over her head, to land deeper into the scrub. Startled, she flattened herself, whiskers twitching.
    A dinosaur was standing stock-still in the shallow water. She was tall and upright, some nine meters tall, with a jaw like a crocodile’s and a great purple-red sail on her back. Her teeth were