You are in the oceans of North America, 75 million years ago.

The water was only waist-deep, a warm, bright turquoise that allowed the sun to paint dancing caustic patterns on the fine, sandy bottom of the Cretaceous sea. In your diving suit, you were scanning the shallow floor, looking for a break in the monotony of algae, when you saw them—not one, but a dozen or more, huddled together like a lost collection of walking sticks.

They were Baculites, the straight-shelled cousins of the coiled ammonites, standing almost vertically in the water column, their shells—white with delicate, dusky brown markings—anchored just barely above the seabed.

As you moved closer, a few of them tilted slightly, perhaps disturbed by the displacement of water. They weren't moving quickly; in fact, they seemed remarkably passive, suspended in a "shale" of their own making, perhaps feeding on the microscopic plankton drifting in the tranquil water. Their long, straight, tubular shells, some perhaps a foot or more in length, shimmered with a faint, faint hint of iridescence, almost like mother-of-pearl, in the sunlight.