Five rocks fit together into one giant hunter.
They had weathered out of a dry hillside in Namibia, and rolled down the slope one by one.
Fitted back together, they hold a skull and a backbone. Only the hips and tail are missing. Whole, this animal was longer than a person.
Its name is Gaiasia, and it lived about two hundred and eighty million years ago.
Its head was broad and flat. At the front, huge fangs in the upper and lower jaws locked together.
It probably lay still near the bottom of the water. Then it opened that mouth wide, and sucked in fish that swam too close.
But this water lay far to the south, closer to the South Pole than to the equator. An ice age was ending.
Its closest known relatives lived in the warm tropics, millions of years earlier.
Scientists thought old animals like these had all been replaced long before.
Yet in the cold south, their line lived on, grew huge, and became the top hunter there.
So the old picture, with these animals only in the tropics, has to be rethought.
Five rocks on a dry hillside, and an old line of hunters turned up where almost nobody had looked.
