Trilobites are extinct, hard-shelled animals that lived in the seas millions of years ago. They evolved at the beginning of the Paleozoic Era (over 500 million years ago) and went extinct during the late Permian period (248 million years ago). The Cambrian Period is known as "The Age of Trilobites."
Trilobites were very common and very diverse; over 15,000 species of trilobites are known. Some trilobites crawled along the sea floor, some swam, and others drifted with ocean currents. The different trilobite species probably had different diets; some were herbivores (eating plants), some were detrivores (eating decayed material) and some were scavengers (eating carrion).
Anatomy: Trilobites were marine invertebrates that had hard, three-lobed shells (the axial lobe and two pleural lobes), hence the name "trilobite". The body is divided into three parts, the cephalon (head), the segmented thorax, and the pygidium (tail piece). These arthropods had jointed legs, compound eyes, and antennae. They ranged in size from less than 1/4 inch (0.6 cm) to over 2 feet (0.6 m) long.
Protection: Many trilobites had protective spines. Some could roll up into a ball, and some could burrow into the sea floor.