Dinosaurs, which roamed the Earth for about 165 million years, became extinct around 66 million years ago, likely due to a combination of catastrophic events, including a massive asteroid impact and volcanic activity. While non-avian dinosaurs are no longer present, their descendants, the birds, are considered modern-day dinosaurs. Fossils and remains of dinosaurs can be found in various locations around the world, providing valuable insight into their existence and evolution.