Shark TeethMohs 3-5
Distinctive crown and root with serrated or smooth blade. Cenozoic phosphate deposits and beach gravels are the productive contexts.
Photo: Momotarou2012 · wikimedia
Fossil Identifier
Fossils preserve organisms across nearly two billion years of Earth history, but the ones you'll actually find while walking a creek, quarry, or roadcut come from a much shorter list. This identifier reads the photo for diagnostic features — sutures, segmentation, growth rings, tooth root and crown — then returns three ranked candidates with geological age, typical host rock, and a similar fossil to rule out.
- Ammonites, trilobites, teeth, plants, bones, coral
- Geological age estimate per match
- Host rock and depositional environment
- Flags modern shells and non-fossil material automatically
Reviewed by RockHoundR Field Team · Field identification & geology editors · Last verified
Quick answer
Photograph a single fossil specimen showing its diagnostic feature — sutures, segmentation, tooth crown, growth rings. The identifier returns three ranked matches with geological age, typical host rock, and a similar fossil to rule out.
Most fossils that turn up in casual collecting come from a few groups: marine invertebrates (ammonites, trilobites, brachiopods, crinoids), plant material (petrified wood, leaf impressions), vertebrate teeth (shark teeth, mammal teeth), and assorted shells and bones. Each group has a small set of diagnostic features that separate it from the others — and from non-fossil lookalikes like modern beach shells.
Geological context narrows the answer fast. A coiled, ribbed shell with suture lines in a Cretaceous chalk is almost certainly an ammonite; the same shape in a Paleozoic limestone is more likely a nautiloid. The identifier accepts an optional host-rock or formation note and uses it to weight regionally and stratigraphically common identifications without inventing locality details.
Photo identification is solid for distinctive groups (ammonites, trilobites, shark teeth, petrified wood) and weaker for incomplete or eroded material. The result is a starting point — confirm with reference fossils in a local museum collection or a state geological survey publication before committing to a species-level call.
Visual identification guide for fossils
Reference specimens for the most-found fossil groups. Each card shows the diagnostic feature that separates it from a modern lookalike.
Petrified WoodMohs 6.5-7
Preserves growth rings and cell structure. Mohs 7 — the silica replacement is as hard as quartz. Found across the American West.
Photo: Mauro Cateb · wikimedia
Bivalve-like shells with bilateral symmetry running through the hinge axis. Most diverse in Paleozoic marine limestones.
Photo: Wikipedia contributors · wikipedia
BelemniteMohs 3-4
Bullet-shaped cephalopod guards. Smooth, often calcite-replaced. Mesozoic marine deposits.
Photo: Tommy from Arad · wikimedia
Megalodon ToothMohs 3-5
Massive serrated crown, distinct chevron above the root. Miocene to Pliocene phosphate units in the southeastern U.S.
Photo: Brocken Inaglory · wikimedia
TektitesMohs 5.5-6.5
Impact-glass — not strictly a fossil, but commonly found alongside them. Dark glassy spheres or splash forms.
Photo: ficusdesk · wikimedia
Fossil identification by host rock
Host rock and depositional environment narrow the candidate list before you even look at the specimen. The table shows where each fossil group typically occurs.
| Specimen | Age | Typical host rock | Field tell |
|---|---|---|---|
| Shark Teeth | Devonian to Recent | Phosphate, marine sandstone, beach gravels | Crown + root + serrated or smooth blade. Modern teeth are white; fossils are darkened. |
| Petrified Wood | Devonian to Pliocene | Continental sandstones and ash deposits | Growth rings visible. Mohs 7 (silica replacement). |
| Brachiopod | Cambrian to Recent (peak Paleozoic) | Marine limestone and shale | Symmetry axis runs through the hinge, not between the valves. |
| Belemnite | Carboniferous to Cretaceous | Marine shale and limestone | Bullet-shaped calcite guard. |
| Megalodon Tooth | Miocene to Pliocene (~23–3.6 Ma) | Phosphate, marine sand | Chevron at the root–crown junction; size (up to 18 cm). |
| Tektites | Variable (impact event) | Strewn fields from meteorite impacts | Glassy black, often splash forms (teardrops, dumbbells). |
Common fossils we identify
Ammonites
Coiled, ribbed cephalopod shells with suture lines visible on weathered surfaces.
Trilobites
Three-lobed Paleozoic arthropods with segmented bodies. Best preserved in shale.
Shark teeth
Serrated or smooth crowns with a clear root. Common in Cenozoic phosphate.
Crinoid stems
Stacked disk segments from ancient sea lilies. Limestone and shale.
Brachiopods
Bivalve-like shells with bilateral symmetry through the hinge — not through the valves like a clam.
Petrified wood
Mineralized wood preserving growth rings and cell structure. Mohs 7 — feels like quartz.
Identify by host rock
The rock around a fossil narrows the candidate list before you even look at the specimen.
- Marine limestone (Paleozoic)
- Brachiopods, crinoids, corals (rugose, tabulate), bryozoans, trilobites.
- Marine shale (Paleozoic)
- Trilobites, graptolites, ammonoids (early forms), conodonts (microscopic).
- Marine limestone / chalk (Mesozoic)
- Ammonites, belemnites, bivalves, gastropods, foraminifera.
- Marine phosphate (Cenozoic)
- Shark teeth, marine mammal bones, fish fossils.
- Continental sandstone / ash (Mesozoic+)
- Petrified wood, dinosaur bone, leaf impressions, freshwater bivalves.
- Lake sediments (Cenozoic)
- Fish, frog, plant impressions (the Green River Formation is the iconic example).
Identify by visible feature
The feature that survived preservation is often the strongest taxonomic cue.
- Suture lines on a coiled shell
- Ammonite (Mesozoic — complex suture) or nautiloid (Paleozoic — simple suture).
- Segmented body in three lobes
- Trilobite. Lobes run head-to-tail and side-to-side.
- Stacked disk segments
- Crinoid stem. Sometimes a whole calyx survives at the top.
- Growth rings in stone
- Petrified wood. Silica replacement preserves cell structure.
- Serrated crown with a clear root
- Shark tooth. Genus and age narrowed by serration pattern and crown shape.
- Bilateral symmetry through the hinge
- Brachiopod (not a clam — clams are symmetric between the valves).
How the fossil identifier works
- Step 1
Upload a clear photo
Show diagnostic features — sutures, segmentation, growth rings, tooth root. JPG, PNG, or WebP up to 6MB.
- Step 2
Add host rock or formation (optional)
Devonian shale, Eocene phosphate, Cretaceous chalk — formation context narrows likely organisms quickly.
- Step 3
Get likely matches with age
Each result includes geological age, typical host rock, diagnostic clues, and a similar fossil to rule out.
Take a photo that identifies well
- Show diagnostic features — sutures, segmentation, growth rings, tooth root.
- Include both sides if the fossil is asymmetric (e.g. shark tooth root vs blade).
- Add a scale (coin, hand) — fossil size often disambiguates species.
- Natural daylight beats flash for reading texture.
What to avoid
- Photos of just matrix with no fossil visible.
- Heavily eroded specimens — wait until you find a better one.
- Through-glass display-case shots.
- Cropping out the diagnostic feature (tooth tip, suture line).
How accurate is this fossil identifier?
Distinctive groups identify well from a photo. Eroded or incomplete material drops accuracy fast — show both sides and a scale when possible.
Strong on
- Distinctive groups: ammonites, trilobites, shark teeth, crinoid stems, petrified wood.
- Telling modern shells from fossils — preservation features differ.
- Naming the host rock and depositional environment for each candidate.
Less reliable on
- Isolated bone fragments — vertebrate paleontology often needs species-specific anatomy that erodes off.
- Partial trilobites without the cephalon (head) — pygidium-only fragments are tough.
- Burrows, traces, and trace fossils — these often need outcrop context the photo can't show.
- Genus-level identification of ammonites — many species share gross morphology.
Want unlimited IDs in the field?
The RockHoundR app works offline, saves every find to your map, and overlays them onto 250,000+ rockhounding spots with geology and land-access data.
Fossil Identifier FAQ
Is this fossil identifier free?
Yes. Upload a fossil photo and get identification results in the browser at no cost. Three free identifications per day per device, no signup, no install. The RockHoundR app removes the daily limit and adds offline use and saved finds.
What kinds of fossils can I identify?
Common groups rockhounders and amateur paleontologists find: ammonites, trilobites, brachiopods, crinoids, shark teeth, petrified wood, fossil bone, plant impressions, corals, bryozoans, and a long tail of bivalves and gastropods. Rare or specialist fossils may identify only to group level.
How accurate is photo-based fossil identification?
Photo ID works well for distinctive groups (ammonites, trilobites, shark teeth, petrified wood). Less complete material — bone fragments, isolated impressions, eroded specimens — benefits from showing both sides and a scale. The tool returns three ranked candidates with a similar fossil to rule out for each.
Why does it ask about the host rock or formation?
Geological context narrows possibilities fast. A coiled shell in Cretaceous chalk is almost certainly an ammonite; the same shape in a Paleozoic limestone might be a nautiloid. The host-rock field is optional and never invented — it only weights stratigraphically common candidates.
Can it tell modern shells from fossils?
Yes. The identifier flags non-fossil material so you don't get a misleading ID on a beach-worn modern shell or recent bone. Preservation features — calcite replacement, host-rock cementation, mineral infilling — differ from anything you'd find on living material.
Will it estimate value?
No. This tool focuses on identification and field context, not appraisal. Many fossils have legal collection rules — always check before keeping material from public land. Federal lands (BLM, USFS) typically allow casual invertebrate and plant collection but restrict vertebrate fossils.
References & sources
Property data and reference imagery used on this page are cross-checked against the following sources.
- Paleobiology Database
Open database of fossil occurrences worldwide — reference for age and host rock data.
- Smithsonian Paleobiology
Reference imagery and group-level taxonomy for the visual identification guide.
- USGS Paleontology Resources
Federal guidance on host rock formations and stratigraphy.