Dinosaurs lived millions of years ago in various shapes and sizes, from the largest over 30 meters long to the smallest about the size of a chicken. They were reptiles that hatched from eggs and included both herbivores that ate plants and carnivores that ate meat. Fossils provide evidence of these extinct creatures, including their bones, claws, eggs, and even plants and insects from the period when dinosaurs inhabited the Earth, though the exact causes of their mass extinction remain unknown.