Dinosaurs were a diverse group of reptiles that lived during the Mesozoic Era, which spanned roughly 180 million years, from about 252 million years ago to about 66 million years ago. This era is divided into three periods: the Triassic, Jurassic, and Cretaceous.
### Key Characteristics:
1. **Bipedal and Quadrupedal**: Dinosaurs came in various forms, with some being bipedal (walking on two legs) and others quadrupedal (walking on four legs).