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. 

Next to dinosaur fossils, trilobites command a dedicated and passionate following amongst both scientists and fossil collectors, alike.  In a relatively short time-frame (scientifically speaking, of course), we have the emergence and subsequent extinction of these fascinating creatures.  Still most baffling is the incredible diversity of sizes and features that made up the trilobite group.  Many bizarre species co-existed with highly specialized body parts that defy the theories of evolution in their "sudden" emergence and diversity during the Early Cambrian Period in what is known as the 'Cambrian Explosion'.