Dinosaurs were pre-historic reptiles that first appeared 231 Million years ago during the Triassic period. They were most dominant during the Jurassic period (200 million years ago) until the end of the Cretaceous period (66 Million years ago), when a Catastrophic event caused the demise of 75% of all plant and animal species on Earth, including all non-avian dinosaurs*
Dinosaur remains have been found on all continents. The largest were 30 metres long and 15 metres high. The smallest was the size of a chicken. They were both herbivores and carnivores, bipedal and quadrupedal
*Due to the high level of iridium (found rarely on the Earth’s crust but commonly on asteroids) identified in rock layers of that time, it is generally thought that impact from asteroids or a large comet created the catastrophe 66 million years ago. This would have impacted greatly on the environment, causing major climatic changes which most species could not cope with.