Dinosaurs first appeared on Earth 230 million years ago! Did you know: * The brachiosaurus was 40 feet tall? * There were once about 500 different dinosaur species? * The hadrosaurus had 250 teeth in its mouth at one time? Dig into BIG DINOSAURS to find out all about the coolest reptiles to ever walk the planet.Dinosaurs first appeared on Earth 230 million years ago! Did you know: * The brachiosaurus was 40 feet tall? * There were once about 500 different dinosaur species? * The hadrosaurus had 250 teeth in its mouth at one time? Dig into BIG DINOSAURS to find out all about the coolest reptiles to ever walk the planet.