The footprint, the shell shape, the leaf print, the bone and the trilobite all came from living things long ago.

Each one has lasted until today.

Some are a part of the living thing: the bone, the trilobite's shell.

Some are a mark it made: the footprint, the shell shape, the leaf print.

Such a part or mark, from a living thing long ago, that has lasted until today, is called a fossil.

Fossils: parts of a living thing, and marks a living thing made.

A fossil is not only a dinosaur bone.

A footprint is a fossil. A leaf print is a fossil.

A shell is a fossil, and so is a tooth.

And a fossil is not the living thing itself.

The soft body rotted away long ago. The hard part, or the mark, is what lasted.