A trilobite was a small ocean animal that lived hundreds of millions of years ago and is now extinct. These creatures had hard, segmented shells that protected their soft bodies, similar to how a pill bug has armor today. The name comes from their three-lobed body structure: if you looked at a trilobite from above, you'd see it divided into three lengthwise sections.

Trilobites thrived in Earth's ancient seas for nearly 300 million years, which is an incredibly long time. They came in many sizes, from smaller than your fingernail to as long as your arm. Most crawled along the ocean floor eating whatever they could find, though some could swim and others burrowed in the mud.

Scientists know so much about trilobites because their hard shells fossilized (turned to stone over millions of years) extremely well. Finding a trilobite fossil is exciting because these animals lived long before dinosaurs even existed. In fact, by the time the first dinosaurs appeared, trilobites had already been extinct for millions of years. Today, paleontologists study trilobite fossils to understand what Earth's ancient oceans were like and how life evolved over time.