Major Dinosaur Groups

Major Dinosaur Groups

Dinosaurs are traditionally divided into two main hip‑based groups, with many subgroups.

1. Saurischia ("lizard‑hipped" dinosaurs)

Includes:

• Theropods – mostly bipedal carnivores, later including feathered forms and birds.
  • Examples: Tyrannosaurus rex, Velociraptor, Allosaurus.
• Sauropodomorphs – long‑necked herbivores and their early relatives.
  • Examples: Diplodocus, Brachiosaurus, Apatosaurus, titanosaurs.

Key features:

• Hip structure similar in some ways to modern lizards.
• Includes the lineage that leads to birds (small feathered theropods).

2. Ornithischia ("bird‑hipped" dinosaurs)

Almost all herbivores, with a hip structure superficially similar to birds (but birds actually evolved from saurischian theropods).

Major ornithischian groups:

• Ceratopsians – horned dinosaurs (e.g., Triceratops).
• Hadrosaurs – duck‑billed dinosaurs, often in herds.
• Stegosaurs – plated dinosaurs (e.g., Stegosaurus).
• Ankylosaurs – heavily armored, low‑slung herbivores with tail clubs.
• Pachycephalosaurs – dome‑headed dinosaurs, possibly used for display or head‑butting.

These groups occupied many ecological roles: large grazers, browsers, specialized plant‑eaters, and more.