How to Identify Trilobites

Trilobites are fossil arthropods, relatives of spiders and horseshoe crabs. They are some of the most attractive and highly sought after fossils. There are many kinds of trilobite fossils, and most have features that they all share. Here are some easy steps to help you identify trilobites.

Difficulty: Moderate

Instructions

1. Learn about the age of the rock where you locate your fossil. You'll only find trilobites in rocks from the Paleozoic Era. If your rock is more recent than this, the fossil is not a trilobite, but may be some other kind of arthropod.

2. Look for trilobites only in marine rocks, such as shale and limestone.

3. Take note of the body of a trilobite. Like all arthropods, trilobites have jointed bodies that are broken into three parts. They have a head (cephalon) that is shaped like a half-circle, a central part (thorax) composed of many segments and a rear part (pygidium) shaped like a half-circle.

4. Notice the trilobite fossil's shiny appearance with patterns of ridges, honeycombs and bumps. These patterns may help differentiate trilobites from one another.

5. Use a detailed fossil guidebook to help you identify your particular trilobite fossil. Different trilobites have varying specific characteristics and a fossil guidebook can help you wade through these detailed features.

Tips & Warnings

• The cephalon and pygidium often resemble each other. The cephalon is the part with the eyes of the trilobite on it.
• Some trilobites have a very small pygidium. The trilobite fossil that you have found may not have a large pygidium.
• Trilobites often broke apart before being fossilized. You may find any piece of a trilobite by itself as opposed to being part of a whole trilobite.

Resources

• Information on trilobites