Evolution What the Fossils Say and Why it Matters

FIGURE 3.1. The process of fossilization destroys 99 percent of the bones and shells of most organisms, so less than
1 percent of all the species that have ever lived are preserved as fossils—and then have the great luck to have been
spotted in the last 200 years when a paleontologist happens to be out collecting.

Footprints are left

in the mud The dinosaur

collapses and dies

Flesh rots away;

bones remain

Time

The water level rises;

sediment buries the bones

and footprints

A thick sequence of

sediments accumulates

over the bones; gradually

the bones fossilize

This bed contains the

dinosaur bones

Erosion exposes the

layer of strata containing

the bones and footprints