Dinosaurs
The dominant land vertebrates for 165 million years — from feathered theropods to horned giants and long-necked titans.
Overview
Dinosaurs are archosaurian reptiles defined by an upright, parasagittal limb posture that made them the dominant large land animals of the Mesozoic. They include the smallest feathered theropods, colossal long-necked sauropods, and armoured and horned ornithischians — and, as living birds, dinosaurs are still with us today.
Quick Facts
Key Characteristics
- •Upright hind limbs held directly beneath the body
- •Reinforced pelvis with an elongated sacrum; perforated acetabulum
- •Skull with openings that lightened the head
- •Theropods: three-toed feet, serrated teeth, feathers in many lineages
- •Sauropodomorphs: columnar limbs, long necks and small heads
- •Ornithischians: bird-like pelvis, often beaks, horns or body armour
Fossil Record
Dinosaur bones, teeth, tracks and eggs are known from Mesozoic rocks on every continent. Exceptional units include the Morrison Formation (USA), Hell Creek Formation, Jehol Biota and Gobi Desert beds (China/Mongolia), Isle of Wight and Lyme Regis (UK), and Patagonian formations in South America. Feathered Chinese specimens have transformed our understanding of their biology.
Global Distribution
Worldwide — every continent including Antarctica has yielded dinosaur remains.
Evolutionary & Scientific Importance
Dinosaurs are central to studies of extinction (K-Pg), the origin of birds and flight, growth rates and gigantism, and ancient continental reconstruction. Their fossil record anchors the vertebrate history of the entire Mesozoic Era.
Classification
The classic two-order split is still widely used, but some recent analyses place theropods with ornithischians — higher-level dinosaur relationships remain actively debated.