Paleontological resources, or fossils, are any evidence of past life preserved in geologic context. They are a tangible connection to life, landscapes, and climates of the past. They show us how life, landscapes, and climate have changed over time and how living things responded to those changes. Those lessons are particularly important as modern climate continues to change.
All fossils are irreplaceable! The National Park Service calls these type of resources "non-renewable." If you find a fossil in a National Park Service area, take a photograph of it, mark its spot on a map, leave it where you found it, and tell a ranger.
Evidence of Life
There are two main types of fossils: body fossils and trace fossils.
Body fossils are any "parts" of the actual living thing: bones, teeth, insect bodies, shells, feathers, leaves, fruits, flowers, nuts, etc.
Trace fossils are "prints and poop"—evidence of a living thing's interaction with its environment, without any part of the actual organism. Footprints, trackways, swim traces, burrows or dens, root traces, and even coprolites (fossil feces) are examples of trace fossils.
As pieces of once living things, body fossils are evidence of what was living where and when. Trace fossils are valuable because they "animate" the ancient animals or plants by recording a moment of an organism's life when it was still alive.