When were dinosaurs last existed?

Dinosaurs first appeared during the Triassic period, about 230 million years ago, and they became the dominant terrestrial vertebrates during the Jurassic and Cretaceous periods. They went extinct around 66 million years ago at the end of the Cretaceous period, likely due to a combination of factors including a massive asteroid impact and volcanic activity that led to significant environmental changes. This extinction event is known as the Cretaceous-Paleogene (K-Pg) extinction event. While non-avian dinosaurs are extinct, it's important to note that birds are considered the modern descendants of some theropod dinosaurs, meaning that in a sense, dinosaurs are still present today through their avian relatives.