FIELD GUIDE

How to identify a fossil

By the Fossil Identifier team · Updated October 1, 2026 · How we prepare our guides

Start with a group, not a species name. A useful first identification might be “shell fossil,” “tooth,” or “crinoid stem.” Shape, repeated structure, and the place it was found are stronger evidence together than any single unusual mark.

A trilobite fossil: look for the repeated segments and central body axis. Photo: National Park Service, Grand Canyon. This is a reference specimen, not an app result.

Features to compare

A visual checklist, not a species diagnosis
Feature	What to look for	What it cannot prove
Coiled shape	Ammonite or another coiled shell	Look for chambers; a spiral alone is not diagnostic.
Repeated plates	Trilobite or another segmented fossil	Check whether segments continue around a central axis.
Small discs or stacked rings	Crinoid stem fragments	Examine the center opening and connected segments.
Pointed crown and broader root	Possible tooth	Photograph both sides and the edge.

Record the find before changing it

Photograph the whole object, both faces, its side profile, and a close-up of the strongest pattern. Place a ruler beside it. Record the nearest locality and whether it was loose or embedded in rock. These notes let you revisit an identification without guessing later.

Compare a feature, not just a silhouette

Ask which visible detail supports the match. If an app suggests a shell, can you see growth lines or shell symmetry? If it suggests a tooth, can you distinguish a crown from a root? Write down details that do not fit as well as details that do.

Know when the evidence runs out

A worn fragment may support only a broad group. Ask a museum or local geology club about unusual material; clear photos, scale, and locality are useful starting information. Leave finds in place where collection is prohibited.

Questions collectors ask

Can I identify a fossil from a photo?

A clear photo can narrow the possibilities. Some specimens need locality information, several views, or examination by a specialist.

Should I wash a fossil first?

Photograph it as found. Avoid chemicals, hard scraping, and breaking it open to reveal detail. Ask for preparation advice if the surface is fragile.

References & further reading

Prepared with AI assistance and linked public educational references. No specialist review is claimed.