Ammonite fossils are found on every continent, in sedimentary rocks that formed in ancient seas between 417 million and 66 million years ago. Because these marine animals were widespread and abundant for over 350 million years, their fossils turn up in limestone, shale, and chalk deposits across dozens of countries. Some locations, though, are far richer than others.
Why Ammonites Are So Widespread
Ammonites were free-swimming and drifting marine animals related to modern squid, octopuses, and nautilus. Some lived near the ocean floor while others floated through the water column carried by currents. This lifestyle, combined with the fact that ancient seas covered vast portions of what is now dry land, means their shells settled into seafloor sediments across nearly every region of the globe. During the Jurassic period alone, researchers have identified roughly 20 distinct biogeographical provinces where different ammonite species thrived, spanning from Arctic waters to tropical seas near the equator and into the Southern Hemisphere.
Ammonites first appeared about 417 million years ago during the Devonian period and survived multiple mass extinctions before finally dying out 66 million years ago when the Chicxulub asteroid impact ended the Cretaceous period. That enormous time range means ammonite fossils appear in rock layers spanning hundreds of millions of years, from Devonian-age formations all the way up to the boundary between the Cretaceous and Paleogene periods. Some evidence even suggests a few species may have lingered for several tens of thousands of years after the impact.
England’s Jurassic Coast
The Jurassic Coast of southern England, particularly around Lyme Regis in Dorset, is one of the most famous ammonite-hunting destinations in the world. Coastal erosion constantly exposes fresh fossils in the cliff faces and deposits them on the beaches, making Lyme Regis one of the best places in the UK for finding ammonites. The rocks here date to the Jurassic period, and ammonites range from thumbnail-sized specimens to dinner-plate-sized coils. The area’s fossil heritage stretches back to the early 1800s, when fossil collector Mary Anning made groundbreaking discoveries along these same shores.
The Western Interior of North America
A massive band of Cretaceous-age shale stretches across the western United States and into Canada, deposited when a shallow sea split North America in two. The Pierre Shale is the most prolific ammonite-bearing formation in this region, with outcrops running from the Black Hills of South Dakota through Wyoming, Montana, Colorado, Nebraska, North Dakota, and northwestern Kansas, extending north into Saskatchewan, Canada.
In Kansas, ammonites are fairly common in Cretaceous outcrops across the central and western parts of the state. One frequently found genus, Baculites, is unusual because its shell is straight rather than coiled. Older ammonite relatives also appear in Pennsylvanian and Permian-age rocks in eastern Kansas, though they’re less common there. These older specimens, found in shale and limestone layers, represent earlier branches of the ammonite family tree from roughly 300 million years ago.
South Dakota’s badlands and the plains of Montana are particularly productive. Fossil collectors regularly find ammonites weathering out of exposed shale hillsides across these states.
Morocco’s Atlas Mountains
The region around Rich and Erfoud in Morocco’s Central High Atlas is one of the world’s largest commercial sources of ammonite fossils. Jurassic and Cretaceous limestone beds here contain enormous concentrations of ammonites, and the fossils are often beautifully preserved. Moroccan ammonites are the ones you’re most likely to see polished and sold in rock shops and online, sometimes sliced in half to reveal the internal chamber structure. The area around Rich has been studied extensively, with rock sections yielding ammonites from multiple distinct time zones within the Jurassic, separated by erosional gaps that represent millions of missing years.
Other Notable Locations
Madagascar produces large, often iridescent ammonite fossils from Cretaceous-age deposits, some exceeding two feet in diameter. Germany’s Solnhofen limestone and Posidonia shale (the same formations known for Archaeopteryx) yield exceptionally well-preserved Jurassic ammonites. In France, Jurassic and Cretaceous exposures across several regions produce abundant specimens. India, Japan, and Antarctica all have significant ammonite-bearing formations as well, reflecting just how thoroughly these animals colonized the world’s oceans.
Alberta’s Iridescent Ammolite
In southern Alberta, Canada, a specific type of ammonite fossil has been transformed into a gemstone called ammolite. The shell material, originally made of the mineral aragonite, developed a vivid rainbow iridescence during fossilization. This gem-quality material comes exclusively from the Bearpaw Formation, a Late Cretaceous deposit roughly 70 to 75 million years old. Only two ammonite species, both in the genus Placenticeras, produce the effect. Ammolite is mined commercially and was designated an official gemstone by the World Jewellery Confederation in 1981.
What Rocks to Look For
Ammonites are preserved almost exclusively in sedimentary rocks that formed in marine environments. The most common host rocks are shale (compressed mud from ancient sea floors), limestone (formed from accumulated shell and coral debris), and chalk (a soft limestone made from microscopic marine organisms). If you’re looking at igneous or metamorphic rock, you won’t find ammonites. The key is identifying areas where ancient seabeds are now exposed at the surface, which happens through uplift, erosion, and road cuts through hillsides.
Cretaceous and Jurassic formations are the most productive, but ammonites also appear in older Devonian, Carboniferous, and Permian rocks. Geological survey maps for your area, often available free online through national geological surveys, will show you the age and type of surface rock near you.
Rules for Collecting
If you’re in the United States, the Bureau of Land Management allows casual collection of common invertebrate fossils, including ammonites, on BLM-managed public land without a permit. You can collect up to 25 pounds per day per person using non-powered hand tools, with only surface collection or minimal digging allowed. The fossils must be for personal use and cannot be sold or bartered. Power tools and heavy equipment are prohibited.
Vertebrate fossils (bones, teeth, trackways) and uncommon invertebrate fossils are a different story and require a research permit to collect. When in doubt about whether a fossil qualifies, leave it in place. Rules differ on state land, national park land, and private property. In the UK, collecting from beaches is generally permitted, but cliff digging may require landowner permission. Morocco has its own export regulations for commercially mined fossils. Always check local rules before you head out with a rock hammer.