Dinosaurs

Definition

Dinosaurs are a diverse group of reptiles that dominated terrestrial ecosystems during the Mesozoic Era. They are characterized by unique anatomical features such as upright limbs and diverse adaptations for different modes of life.

5 Must Know Facts For Your Next Test

1. Dinosaurs first appeared approximately 230 million years ago during the Triassic period.
2. The Mesozoic Era, often called the Age of Dinosaurs, includes three periods: Triassic, Jurassic, and Cretaceous.
3. There were two major groups of dinosaurs based on hip structure: Saurischia (lizard-hipped) and Ornithischia (bird-hipped).
4. Modern birds are considered descendants of a group of theropod dinosaurs.
5. The mass extinction event at the end of the Cretaceous period, around 66 million years ago, led to the extinction of most dinosaur species.

Review Questions

• During which geological era did dinosaurs dominate terrestrial ecosystems?
• What are the two major groups of dinosaurs based on hip structure?
• Which modern animals are considered descendants of theropod dinosaurs?

Related terms

Saurischia: Dinosaurs with lizard-like hips, including theropods and sauropodomorphs.

Ornithischia: Dinosaurs with bird-like hips that include herbivorous species like Stegosaurus and Triceratops.

Theropods: A subgroup of saurischian dinosaurs that includes bipedal carnivores like T-Rex and ancestral birds.