Geological periods
Fossil Sites by Geological Period
The age of the rock decides what you can find in it. A Devonian limestone will never hold a dinosaur, and a Miocene beach cliff will never hold a trilobite. Work out which period is exposed near you, and the list of possible finds narrows immediately.
How to read the sequence
Geologists divide the last 4.6 billion years into named intervals. The boundaries are not arbitrary. Most of them mark a real change in what lived on Earth, and several mark extinctions severe enough to reset the fossil record entirely.
The dates below are in millions of years before the present, written as Ma. They follow the International Commission on Stratigraphy. The counts show how many documented sites on this website expose rock of that age, which is a measure of our coverage rather than of the rock itself.
One caution when you use these pages. A site is filed under the period of its principal fossil-bearing unit, but many locations expose more than one. Death Valley is filed as Neogene for its Pliocene trackways, and it also exposes Precambrian stromatolites and Cambrian trilobites in the surrounding mountains.
Precambrian
Nearly 4 billion years, and almost no hard parts. What survives is mostly stromatolites, the layered mounds built by microbial mats, plus the soft-bodied Ediacaran organisms near the end of the interval.
Paleozoic
Shelly life appears, diversifies, and is repeatedly cut back. This era gives collectors the classic invertebrate faunas: trilobites, brachiopods, crinoids, corals, and graptolites. It closes with the largest extinction in the record.
- Cambrian538.8 – 485.4 Matrilobites (Paradoxides, Olenellus, Elrathia), brachiopods, sponges, archaeocyathids, and rare soft-bodied Burgess Shale-style biotas. 6 sites
- Ordovician485.4 – 443.8 Matrilobites, brachiopods, graptolites, nautiloids, early corals, crinoids. 21 sites
- Silurian443.8 – 419.2 Matrilobites (Calymene, Dalmanites), brachiopods, eurypterids (sea scorpions), graptolites, early jawed fish. 9 sites
- Devonian419.2 – 358.9 Maplacoderms, early sharks, ammonoids (goniatites), trilobites (Phacops, Drotops), brachiopods, corals, Devonian reef fossils. 30 sites
- Carboniferous358.9 – 298.9 Macrinoids, brachiopods, corals, plant fossils, primitive shark teeth, Tully Monster, giant arthropods. 18 sites
- Permian298.9 – 251.9 Masynapsid reptiles, brachiopods, ammonoids, fusulinid foraminifera, plant fossils. 4 sites
Mesozoic
The age of ammonites, marine reptiles, and dinosaurs. Marine mudstones and limestones from this era produce most of the fossils people picture when they think of fossil hunting, and most of the sites on this website.
- Triassic251.9 – 201.4 Maearly dinosaurs, ichthyosaurs, ammonites, Tasmanian fossil cliffs at Maria Island, Triassic conodonts. 11 sites
- Jurassic201.4 – 145.0 Maammonites, belemnites, ichthyosaurs, plesiosaurs, dinosaurs, Solnhofen Archaeopteryx, Posidonia Shale ichthyosaurs. 53 sites
- Cretaceous145.0 – 66.0 Madinosaurs, ammonites, mosasaurs, shark teeth, flowering plant fossils, K-Pg boundary clay. 79 sites
Cenozoic
Mammals expand, and the shark teeth and shells that dominate beach collecting are laid down. The youngest deposits hold Ice Age megafauna, which are often still bone rather than mineralized stone.
- Paleogene66.0 – 23.03 Maearly mammals, sharks, fish, plant fossils, insect fossils, Florissant biota, London Clay. 46 sites
- Neogene23.03 – 2.58 Mashark teeth (including Megalodon), whale teeth, marine mammal bones, Pliocene megafauna, hominid fossils. 48 sites
- Quaternary2.58 Ma – presentmammoths, mastodons, ground sloths, sabre-toothed cats, dire wolves, La Brea biota, cave-bear remains. 23 sites
Other ways to browse
Period is one route into the catalogue. Browse by fossil type if you know what you want to find, by US state or by country if you know where you are going, and the regional guides if you want a ranked shortlist for one area.