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Facts, Information, Types of Trilobites


Facts and Information

Trilobite Facts

Fossil Hunting for Trilobites

Fast Facts about Trilobites

Three Cryptolithus trilobites from Swatara Gap in Central Pennsylvania

Name: Trilobite (pronunciation: "TRY-loh-bite") - The name means "Three Lobes"

Taxonomy: Phylum: Arthropod - Class: Trilobita
Trilobites are arthropods, think of them as crab like animals, not bugs!
They are a very diverse Class of animal. There are 10 orders in the class:
Agnostida, Asaphida, Corynexochida, Harpetida, Lichida, Odontopleurida, Phacopida, Proetida, Ptychopariida, and Redlichiida
There is a bewildering amount of Trilobite species. Best estimates put this number to over 20,000 species.

Age: Pre-Cambrian to Permian
Trilobites are one of the most successful animals to live on Earth.
They were already here before the Cambrian explosion, survived numerous mass extinctions and lived until the end Permian extinction event, the end of the Paleozoic age.
This clade lived for around 300 million years!

Discovery: Trilobites, a common fossil, were known to people throughout history.
The first "scientifically" described trilobite comes from Wan Shizen of China. In 1689 he described trylobite pygidia (tails) as batstones.
The first scientific drawing of a trilobite comes from Rev. Edward Lhwyd. He has a sketch of a trilobite in the 1698 volume of "The Philosophical Transactions of the Royal Society". The trilobite, which we know as Ogygiocarella debuchii, is called a "flatfish".

Distribution: Global:
Trilobites lived in the seas and oceans all over Earth. Thier fossils are found on every continent.

Body Size: 1 mm to 72 cm in size!
The smallest trilobite is currently Acanthopleurella stipulae at around 1 mm, that's the size of a fleck of pepper.
The largest trilobite is currently Isotelus rex which has been found to reach 72 cm. That's over 2 feet!

Trilobite diets reflect their diversity. Some were filter feeders, some were scavangers, others were predators. They probably ate anything smaller than themselves, including other trilobites.

Physical Appearance:
They all have the same basic design, three lobes: a left pleural lobe, a middle axial lobe, and a right pleural lobe.
They are also divided into a Cephalon (Head), Thorax (Middle), and Pygydium (Tail).
Trilobites had a thick exoskeleton for protection.
Some have beautiful spines, some have no eyes, some have long tials... the diversity is amazing.

Some Could Enroll:
Some trilobites could enroll them selves into a ball for protection, similar to what little pill bugs do.

Trilobites Molted:
Like crabs and lobsters, trilobites had to molt when growing. Just after molting, or shedding their exoskeleton, they were soft and vunerable. Most trilbite fossils are actually molted exoskeletons.

First Compound Eyes:
Trilobites appear to be the first form of life to have complex eyes. Many species have eyes that contain numerous lenses made of crystals!

Yes They Have Legs:
Most fossil trilobites are simply their exoskeletons. However, rare fossils preserve their soft body parts. These include legs, gills, antenna, and other appendages.

This is a pyritized Triarthrus eatoni trilobites with soft appendages preserved. These amazing pyritized fossils come from New York.
By James St. John [CC-BY-2.0] - Image has been rotated.

Introduction to Trilobite Fossils - Trilobite Fossil Facts and Information

This image shows the three lobes of a trilobite (what they are named after), and also the 3 segments of a trilobite. The specimens pictured here are Elrathia kingii trilobites from Utah.

What is a Trilobite Fossil?

Various types of Trilobites

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!

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.

Exoskeleton and Trilobite Enrollment

This shows pyritized Triarthrus trilobites with their soft appendages preserved. These amazing fossils come from Beecher's Trilobite Bed in NY.
By Didier Descouens (Own work) CC-BY-SA-3.0-2.5-2.0-1.0]

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.

Diagram of enrolled trilobites. All of these trilobites were found in various places in Ohio. They include Gravicalymene, Flexicalymene, and Phacops

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.

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.

Looking for Trilobites in Utah. Here is a nice orange Ausphiscus wheeleri that will prep out beautifully!

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 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 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-

Recommended Trilobite Books and Fossils

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!

Recommended Books

The Trilobite Book: A Visual Journey
by Dr. Riccardo Levi-Setti, 2014

This is an updated (2014) hardcover (kindle available) of his famous 1994 book. It now has color images instead of black and white ones. The images are of prefectly prepared trilobites from all over the world. this book is geared toward the beginner and does not get overly technical. However, it's wonderful just to see the pictures, and a must for any trilobite enthusiast.

Trilobite: Eyewitness to Evolution
by Dr. Richard Fortey, 2001

Dr. Fortey is a famous natural history writer from the British Museum of Natural History. He brings trilbites to life in this well crafted and enjoyable narrative. He merges science and history together to show us the big picture about trilobites. It's a nice read for anyone interested in Trilobits.

Trilobites: Common Trilobites of North America (A NatureGuide Book)
by Jasper Burns, 2000

I love Jasper Burns. His Fossil Collecting in the Mid-Atlantic book is still one of my favorite fossil books. His drawings are spectacular and the books are well laid out. This book serves as a field guide and identification guide to North American trilobites. If you fossil hunt for trilobites in North America, you should have this book!

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.

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