Trilobites were remarkable, hard-shelled, segmented creatures that existed over 520 million years ago in the Earth's ancient seas! Although all extinct now, (they went extinct before dinosaurs even came into existence!) they represent among the first explosions of biological diversity that this amazing planet of ours has generated over time.  Two Skies source Elrathia Trilobites from Utah, USA (flatter, black fossils)  and Phacopida Trilobites from Morocco (amazing three dimensional fossils).