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Fossil Hunting for Trilobites

Introduction to Trilobite Fossils - Trilobite Fossil Facts and Information

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What is a Trilobite Fossil?

The term Trilobite literally means "Three Lobes." The name references the animal's body plan. All Trilobites have three lobes, a left pleural lobe, Axial lobe, and a right pleural lobe. See the image above.

Although they all have three segments, a Cephalon (head), Thorax (body), and Pygydium (tail), the "Three Lobes" do not refer to this.

Trilobites are Arthropods. They look like little hard shelled insects, and are often nicknamed "bugs" by fossil collectors, but they are not related to insects. Trilobites are an extinct clade of Arthropods (like crustaceans). Nothing like them exists today. They are, however, distantly related to the chelicerates clade. Chelicerates include horseshoe crabs and spiders. Think of them as little crab like critters.

Trilobites are diverse! They belong to the class called Trilobita. This class contains over 20,000 species of trilobites!

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Trilobite Size

Since there are so many types of trilobites, they came in a wide array of sizes. Some, such as the Perenopsis trilobites, that grew to only a few millimeters in size, and look like flakes of pepper on a rock. The largest, Isotelus rex, from the Upper Ordovician of Manitoba, Canada grew over two feet in length. The worlds largest trilobite specimen of Isotelus rex is recorded at 720 mm, over 2.3 feet in length.

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Exoskeleton and Trilobite Enrollment

Trilobites have a hard calcite shell protecting them, similar to a crab. These exoskeletons are usually the only part of a trilobite that survives fossilization. Their soft parts such as antennae and legs rarely fossilize. A rare example of soft tissue trilobite preservation is shown in the image above.

When a trilobite grew, it molted, i.e. removed its exoskeleton, again, similar to what a crab does. Molted exoskeletons are by far the most commonly found trilobite fossils, they are usually missing segments, such as the cephalon or pygidium.

One interesting characteristic of trilobites is that many could enroll themselves. This enrollment was probably for defensive purposes, as an enrolled trilobite would have all of it's soft body parts protected.

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Trilobite Origins and Extinction

Trilobites probably arose from a soft bodied ancestor in the Pre-Cambrian. The first actual trilobites fossils found are from the Cambrian. Based on the variety of Early Cambrian fossils and the wide distribution, trilobites probably evolved sometime in the Pre-Cambrian.

Once Trilobites made their appearance, they dominated the Paleozoic seas, many new orders and families quickly appeared. They were actually the most diverse class of life on the planet, containing 10 orders, thousands of genera, and over 20,000 species.

However, mass extinctions took their toll on Trilobites. The End Ordovician extinction event took out a few orders of trilobites. Then the End Devonian extinction event removed all but one order of trilobite. When the Great Permian extinction even occurred, which marks the end of the Paleozoic, the last trilobites became extinct. Exactly why one of Earth's most successful and prolific creature could not survive the mass extinctions is still a mystery, and often debated. Fortunately, their hard exoskeletons enabled them to become readily preserved as fossils, and we can enjoy them today.

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Where to Find Fossil Trilobites

Trilobite fossils are incredibly abundant in many Paleozoic outcrops across the planet. Unfortunately, almost all of them come in the form of bits and pieces. Some formations, though, were formed in just the right conditions to leave an occasional whole trilobite.

Some of the more famous locations in the United States where whole trilobites can be found include: Oklahoma, Utah, New York, and Ohio.

Oklahoma
Oklahoma has the world famous Devonian Haragan and Bois d' Arc Formations. These formations have a similar trilobite fauna as the Morocco Devonian trilobites, however the preservation is similar to the famous St. Petersburg Russian trilobites.
-Oklahoma Trilobite Hunting Trip Report here-

Utah
Utah has the famous Cambrian Wheeler and Marjum Formations exposures which have a plethora of beautiful trilobites. Americas famous little trilobite, Elraithi Kingii, is found here en masse.
-Utah Trilobite Hunting Trip Report here-

New York
New york has famous exposures all over the state that contain beautifully preserved trilobites. These exposures also extend through many time periods, including the Devonian and the Ordovician.
-Western New York Trilobite Fossil Site-

Ohio
Ohio has a world famous Devonian exposure called the Silica Shale. It contains Eldredgeops (Phacops) rana trilobites that tend to be a little larger than other collecting locations.
-Silica Shale of Ohio Trilobite Fossil Site-

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Recommended Trilobite and Fossil Hunting Books:

Trilobites for Sale:

Trilobites from Fossil Era
Trilobite fossils are some of the most beautiful and collectible fossils in the world! There are countless species of trilobites. They make beautiful display and conversation pieces. Common ones make very affordable for gifts to fossil and paleontology enthusiasts. Fossil Era has a huge selection of top quality trilobites from many states and many countries. It's fun just to browse through the inventory and look at all the different types!

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Trilobite Fossil Gallery

Browse through the different types of trilobites and learn about each trilobite fossil. Each type of Trilobite is linked to facts, collecting sites, trips, images, and additional information. The fossil trilobites are sorted by geologic time period.

Click on any of the images below to go to the specific trilobite page.