Dinosaurs first appeared during the Middle to Late Triassic period, around 230 million years ago, as relatively small and unassuming creatures. Early species like Eoraptor and Herrerasaurus were bipedal predators no larger than a dog. But following the end-Triassic extinction event, which wiped out many of their competitors, dinosaurs rapidly diversified and rose to ecological dominance -- a reign that would last over 160 million years.
The diversity of dinosaurs was staggering. Sauropods like Argentinosaurus grew to lengths exceeding 30 meters and weights of 70 tonnes, making them the largest land animals ever to exist. Theropods ranged from the terrifying Tyrannosaurus rex, with its bone-crushing bite force, to small feathered forms that would eventually give rise to birds. Ceratopsians sported elaborate horns and frills, while ankylosaurs armored themselves like living tanks.
Dinosaurs weren't just large reptiles -- they were highly sophisticated animals. Many theropods were covered in feathers, used for insulation, display, and eventually flight. Evidence of parental care, herding behavior, and complex social structures has been found across multiple lineages. Some species may have been warm-blooded or at least had metabolic rates far higher than modern reptiles, enabling active lifestyles in a variety of climates.
The age of dinosaurs came to a catastrophic end 66 million years ago when a massive asteroid struck what is now the Yucatan Peninsula in Mexico. The impact triggered global wildfires, a "nuclear winter" of dust and debris, and acid rain that devastated ecosystems worldwide. Around 75% of all species went extinct, including all non-avian dinosaurs. But their legacy lives on: modern birds are living dinosaurs, the direct descendants of small feathered theropods that survived the apocalypse.