Dino Detectives: How Fossils Tell Us About Dinosaurs

No person has ever seen a living dinosaur — the last ones died out 66 million years ago. So how do we know dinosaurs had sharp teeth, or that some were as tall as a building? Scientists called paleontologists act like detectives, using clues left in rocks called fossils to solve the mystery.

- Say what a fossil is and how it forms - Name three different dinosaurs and one fact about each - Explain how scientists use fossils as clues - Match a dinosaur to a clue about how it lived

A fossil is what's left of a plant or animal that lived a very long time ago, usually turned to stone. When a dinosaur died millions of years ago, sometimes its bones got covered by mud or sand very quickly. Over a huge amount of time, minerals slowly replaced the bone material, turning it to rock while keeping the same shape. That rock-hard copy of the bone is the fossil we dig up today.

Tyrannosaurus rex, or T. rex, had teeth up to 8 inches long — as long as a banana — which tells scientists it hunted and ate meat. Triceratops had three horns on its face and a bony frill, which likely protected it from predators like T. rex. Brachiosaurus had an extremely long neck, letting it reach leaves at the tops of tall trees that shorter dinosaurs couldn't reach.

Brachiosaurus could grow to about 60 feet long — roughly the length of two school buses parked end to end — and its head could reach as high as a four-story building. Not all dinosaurs were giant, though. Compsognathus was about the size of a chicken. Fossils let scientists measure bones and figure out exactly how big each dinosaur really was.