About 70 million years ago, the Earth's continents and oceans began to resemble the shapes we are familiar with today. The Atlantic Ocean separated the Americas from Europe, Asia and Africa.

About 70 million years ago, during the Late Cretaceous Period, sea levels were higher than they have been since. Much of North America was covered by water, and the animals seen here lived in a sea that covered present-day Tennessee. At left, the animal with a spiral shell and tentacles is an ammonite, an extinct relative of the squid. The corkscrew-shaped animal in the foreground is also an ammonite.

A close living relative of the ammonite, the chambered nautilus (Nautilus pompilius) lives at great depths and is an active swimmer.

Ammonites are spiral- and straight-shelled mollusks that were once abundant and widespread in shallow marine seas. These animals became extinct at the end of the Cretaceous Period, 65 million years ago, at around the same time as the dinosaurs. Despite their large shells, ammonites were capable of swimming, although they probably hovered just above the sea floor.