The fossil record shows that dinosaurs first appeared during the Triassic period around 230 million years ago, evolving from earlier archosaur ancestors. Over the next 165 million years, they diversified into two main groups—Saurischia and Ornithischia—and adapted to roles as herbivores, carnivores, and omnivores. Their reign ended abruptly around 66 million years ago in a mass extinction event (the K–Pg boundary) likely triggered by a massive asteroid impact and volcanic activity that led to dramatic climate changes. While non-avian dinosaurs vanished, some theropods survived and evolved into modern birds.
- Dinosaurs evolved from archosaur ancestors in the Triassic (~230 Ma).
- They diversified into Saurischia (lizard-hipped) and Ornithischia (bird-hipped).
- The Mesozoic Era is known as the “Age of Dinosaurs” (~252-66 Ma).
- A mass extinction at the end of the Cretaceous (~66 Ma) wiped out non-avian dinosaurs.
- Birds are the living descendants of theropod dinosaurs.
Dinosaurs first appeared during the Triassic period, around 230 million years ago.
The two main groups of dinosaurs are Saurischia and Ornithischia.
Source Material
Author: American Museum of Natural History
Document: Evolution of Dinosaurs: From Origins to Dominance
Date Published: 2023