During the Late Triassic epoch, dinosaurs grew no bigger than today's largest mammals. However, during the Jurassic period, which began 200m years ago, they developed into giants.

How were dinosaurs so large?

Dinosaurs lived during the Triassic, Jurassic and Cretaceous. During these periods, the climate was much warmer, with CO₂ levels over four times higher than today. This produced abundant plant life, and herbivorous dinosaurs may have evolved large bodies partly because there was enough food to support them.

Are dinosaurs really that big?

Most of us imagine dinosaurs as the huge, towering prehistoric beings that once walked the Earth. But it turns out that dinosaurs were actually a wide range of sizes — and some of them weren't much larger than a turkey. Here's how big all the dinosaurs from "Jurassic Park" are relative to an average human man.