Trilobites are hard-shelled, segmented creatures that lived hundreds of millions of years ago in the Earth's ancient seas. They are considered to be one of our planet's earliest complex life-forms and are one of the key signature creatures of the Paleozoic Era. Trilobites went extinct before dinosaurs even existed.
Trilobites were the first creatures with a skeleton (Exoskeleton) so they were easily fossilized. Their shell is divided lengthwise into three lobes (hence, the name TRILOBITE meaning "three-lobed"): a central axial lobe, and two symmetrical pleural lobes that flank the axis.
Morphologically, the trilobite body is divided into three major sections:
1. a cephalon (or head) with eyes, mouthparts and sensory organs such as antennae
2. a middle region called the thorax, made up of a number of overlapping segments (anywhere from 2 to 61)
3. a pygidium (or tail section) in which the segments were fused.